Posted By Daniel Langlois,
Thursday, July 01, 1999
Updated: Wednesday, August 29, 2012
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On August 1, 1998, at approximately 8 p.m., a fire occurred at a single storey, 2,400 sq. ft. log home in a rural area of Stouffville, Ontario. The log home was of main floor open concept design with three bedrooms and three bathrooms. It was originally built in 1964 making the home 34 years old at the time of the fire. The fire originated at the front area of the home directly above the front porch at the roof level. The fire traveled upwards along the frame of the roof line resulting in significant fire damage to half the roof and subsequent heat, smoke, and water damage throughout the home. The damages were estimated at $160,000 to the building and $40,000 damage to the contents.
For purposes of this article, we will refer to the original owner of the subject log home as Ms. A and the owner of the home at the time of the fire as Mr. B.
In late 1992, Ms. A faced some major roof repairs resulting from ice damage. The poorly insulated ceiling caused considerable snow melt on the roof and ice buildup at roof edges, resulting in damage to the roof overhangs. The damage was most severe over the large overhanging front porch of the home.
In October, 1992, Ms. A hired a contractor to replace the shingles over the damaged roof section at the front of the house, and a second contractor to install a 200 foot long, 120 VAC de-icing heating cable on the roof to prevent a recurrence. The heating cable was installed along the overhang and the eaves trough of the roof line at the front of the home. The front of the home faced southwest. No heating cable was installed on either sides or back of the house. A duplex receptacle was installed in the porch area nearest to the eaves trough, and a separate outdoor type switch was installed near the front door to control the receptacle. An additional duplex receptacle, also controlled by the switch, was installed near the front door. While the switch was not identified as to its function, surface mounted conduit used to route the wiring to both receptacles made it quite obvious that the switch controlled these receptacles. The power supply cord for the heating cable was plugged into the receptacle nearest the eaves trough. This particular circuit, protected by a 15 Amp circuit breaker, was shared with some auxiliary lighting exterior to the house.
In June, 1997, Mr. B, the owner of the home at the time of the fire, took possession. Mr. B bought the property and the home for its land potential and recognized that the log home needed some work.
Although the solid log home was well built 34 years ago, it had seen nothing more than obligatory repairs since then. Mr. B and his wife were aware of the outside circuit since it was used to control some external lights which were plugged into the receptacle near the door, but which they had chosen not to use. Therefore, the outdoor switch was usually left in the "off” position. Both Mr. B and his wife were unaware of the heating cable installed on their roof, even though the plug for the heating cable was clearly visible in the receptacle near the eaves trough. The manufacturer’s identification label was also attached to the cable power cord at the plug.
In late July, 1998, Mr. B hosted a children’s theater camp at his home. In preparation for the event, he needed power outside of the home to operate a portable hot tub (approximately 12 amp load). On Friday July 24th, 1998, Mr. B. plugged the hot tub into the receptacle near the door and turned it on, energizing the circuit. Since the heating cable was still connected to the second receptacle controlled by the switch, the total load on the circuit then exceeded 15 Amps. This caused the circuit breaker to trip about 20 minutes later. Mr. B. then removed the hot tub’s power supply cord from the receptacle and inserted it into another inside circuit via an electrical extension cord. Mr. B. also then reset the tripped circuit breaker.
The hot tub began to operate again without difficulty. However, Mr. B. did not return the switch to the "off” position, resulting in the heating cable remaining energized. The days following July 24, 1998, were hot and dry.
On August 1, 1998, the day after the conclusion of the children’s theater camp hosted by Mr. B., the fire occurred. At approximately 8:15 p.m., Mr. B was outside, approximately 150 feet southwest of the house. He became alarmed by a nauseous smell that became more intense with time. It was described as "a smell similar to burning tires.” Mr. B investigated to see if the odour was emanating from his home. At that time, Mr. B’s daughter came out of the front door of the house. When Mr. B turned to talk to his daughter, he noticed smoke coming from the outside of the roof above the front porch eaves trough and down spout. He ran back toward the house and with a closer view, noticed a small flame above the eaves trough and smoke from a radius of approximately two feet coming from leaves on the roof. Within a couple of minutes, Mr. B brought a bucket of water and his garden hose to the front porch. The roof was too high for him to reach and suppress the fire. He threw the running hose onto the roof and proceeded to call 911, advising the fire department of a small fire on his roof that he was trying to bring under control.
During an interview with Mr. B, he explained the fire continued to spread in spite of the running water from the garden hose (There wasn’t much water pressure). Mr. B climbed up the T.V. tower at the northeast side of the home, and proceeded to the area of the fire. He noticed burnt and smoldering leaves one to two feet from the readily apparent flame. The leaves did not appear to be burning. Mr. B directed the garden hose to the base of the flame which appeared to have originated from inside the eaves trough, however the flame and the risk of falling off the roof, kept him at a distance.
Mr. B called 911 a second time when it was apparent the fire was out of control. The flames extended 4-6 inches above the eaves trough. Minutes later, the flame burned through the fascia board of the roof and traveled into the roof and attic space. Mr. B could hear the draft of air being drawn by the fire into the roof and attic and observed smoke coming out of a roof vent nearby. He quickly alerted his family to evacuate the building. Mrs. B shut off the main power switch of the electrical breaker panel on her way out. The master bedroom, immediately adjacent to where the fire started, also caught fire. The newly installed security system, including smoke and rate of rise heat detectors, began to alarm shortly after the bedroom caught fire. By the time the fire department arrived, the roof was fully engulfed in flames. It took more than 30 minutes to put the fire out. There were no injuries.
Investigation based on fire damage and burn patterns revealed the area of fire origin to be at the roof level, adjacent to the eaves trough, directly above the front porch.
The eaves trough was made of metal with a plastic leaf screen. The top of the roof over the eaves trough, where the heating cable was installed, was blanketed with a few inches of dry leaves and small broken twigs and branches. The fire traveled upwards along the frame of the roof line. However, in addition to the fire damage to the roof, the master bedroom and adjacent bedrooms sustained severe heat and fire damage as a result of drop burning.
The heating cable was installed along a 38 foot length of the front roof line, southwest side of the home. There was no heating cable installed on either sides or back of the home. Approximately 29 feet of the front, southwest roof line was occupied by heating cable which was intact. This 29 foot length of roof occupied approximately 83 feet of heating cable which appeared to be properly installed. However, not including the length of heating cable running through the down spout, the remaining 9 foot length of roof (38-29) in the area of fire origin, occupied the remaining 78 feet of heating cable. The entire length of heating cable measured 200 feet long. There was no evidence to suggest that the remaining 78 feet of heating cable on the roof, in the area of fire origin, was correctly installed. Examination of and sifting through fire debris revealed no evidence of mounting clips used for securing the heating cable to the roof shingles. Furthermore, there was only 9 feet of roof line remaining to install 78 feet of heating cable. Based on the roof construction, it appeared the entire remaining length of heating cable was applied to the 9 foot section of roof directly above the front porch, an amount of cable in excess of what should have been applied to this area.
Electrical continuity testing confirmed that the duplex receptacle the heating cable was plugged into was operated by the remote switch mounted on the exterior wall. There was no identification on the switch indicating it operated heating cable installed on the roof. In an interview with Mr. B, he confirmed the exterior wall mounted switch was on and the heating cable was plugged into the duplex receptacle at the time of the fire.
CONCLUSION / RECOMMENDATIONS
The installation of the heating cable was not in compliance with the manufacturer’s instructions, however it was used on a metal eaves trough as recommended.
Information provided by the owner revealed the heating cable installation was unknown by him as he was not notified of the heating cable by the previous owner. Not knowing what the problem was at the time the circuit breaker tripped while operating the portable hot tub, Mr. B re-set the circuit breaker and plugged in his hot tub to another receptacle. The switch he turned on, remained on for eight days, effectively energizing the heating cable for the eight days prior to the fire. If the owner had known what the switch was operating, he likely wouldn’t have left it on. The combination of a dry warm summer, and dry combustible leaves and branches blanketed over the electrical heating cable, coupled with the poor installation and the accidental energizing of the heating cable switch, are the most likely cause of this fire.
As a result of the subject fire, the CSA International, Audits and Investigations Department at the Canadian Standards Association reviewed its computer data base and confirmed this type of incident was the first of its kind. However, a recommendation was forwarded to the sub-committee responsible for CSA International Standard CAN/CSA-C22.2 No. 130.2-93 – "Heat Cable Systems for Use in Other Than Industrial Establishments” to review this information and consider implementing amendments to the referenced standard to prevent a fire recurrence.
The recommendation is currently being reviewed by the sub-committee for action as deemed necessary.
Use and Care of Heating Cables
At least part of the reason for this fire was the improper use and care of the heating cable installation. The build-up of leaves and twigs on the heating cable thermally insulated it and may have led to overheating. Heating cable manufacturers recommend that cables be checked annually to ensure they are in proper working order and capable of performing as expected. Certainly, leaves covering a roof de-icing cable will impede the proper operation of the cables, as heat from the cables will be insulated by the debris, thereby allowing ice to form above the leaves.
Similarly, pipe freeze protection cables must be inspected annually for proper operation and installation. If insulation surrounding pipe heating cables has deteriorated, or if the cable has been damaged in any way, the installation should be disconnected.
If a heating cable, or any other electrical device, is connected to a ground fault protected circuit/receptacle, and the ground fault device trips when the heating cable is connected, the heating cable likely has been damaged and must be removed from service.
It is also important for new homeowners to fully familiarize themselves, not only with any heating cables, but with all electrical devices which may be installed on or in the home. If a new homeowner is unsure about any such electrical devices, a qualified electrician should be consulted for appropriate advice. Similarly, the previous homeowner, or the homeowner’s agent/seller, should also ensure the operation of any non-standard electrical items, such as heating cables and saunas, is appropriately communicated to the new homeowner.
Ground Fault Protection for Heating Cables
The 1998 version of the Canadian Electrical Code Part 1 (CEC), Rule 62-300, provides requirements for ground fault protection for fixed heating cable installations, including those heating systems for melting snow and ice on roofs. In addition, most manufacturers strongly recommend the use of such a device with their products. Most outdoor receptacles on houses constructed since about 1980 contain ground fault devices, which will help to prevent damaged heating cables from being energized. Note, however, that overheating caused by improper heating cable maintenance will not necessarily be prevented by ground fault protection devices, as likely evidenced by this fire. Furthermore, homes built prior to about 1980 may not contain any ground fault protection devices. For these situations, some heating cable companies offer a convenient, economical plug-in ground fault protection device, which can easily be connected by the homeowner (just plugs in to existing receptacle).
Electrical Fire Reporting System
The forwarding of information to CSA International regarding fires involving CSA certified electrical products aids in the facilitation of improving Canadian Standards. Even though fires are reported to a fire department or fire marshal, and the most likely cause of the fire identified and documented, these reports do not always get forwarded to CSA International. This was the case with the fire described in this article, where CSA International were only notified of this fire by a letter from the homeowner written directly to CSA International concerned about how this fire could have happened. It is important that all fires involving electrical products be reported to CSA International’s Audits and Investigations Department. This will ensure that incidents such as this one are properly investigated and documented in the Audits and Investigations computer data base.
Read more by Daniel Langlois
Posted By Michael Johnston ,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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Many businesses are concerned these days with the cost of electrical energy supplying power to their facility, but an increasing number of them are getting real concerned about the quality of the power being utilized at their facility. So what is the problem with the quality of power being delivered to a facility? Many businesses are extremely nervous about loss of data or data errors that can result from this "dirty power” or "electrical noise” on the system. Does this sound familiar? So what do they do? Many have extensive evaluations performed and end up with large surge protectors or filtering systems consisting of metal oxide varistors (MOVs) and capacitors to try and filter or stabilize their electrical supply system. Is that the answer? In some cases these types of devices can be effective in cleaning up some power quality issues.
In large, or even smaller, facilities, if the owner or operator is considering an attempt to clean up the power being delivered to the facility, he should start with an extensive analysis of the serving utility’s power as delivered, the electrical service, the power distribution system, the panelboards, and finally the branch circuits and what is connected to the branch circuits. One of the most important aspects of this analysis is the inspection of the grounding electrode system, the equipment grounding conductors, the bonding system, and the grounded conductor of the system. If an electrical system is not grounded properly, the voltage could be flowing unstably to begin with before it’s filtered. Section 250-2(a) of the 1999 National Electrical Code® specifically states the reasons for grounding electrical systems. The electrical system shall be "connected to the earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines, and that will stabilize the voltage to earth during normal operation.”
The term "quality of power” is often described in different ways and by different elements of the electrical industry. Stabilized voltages and stable waveforms are two elements which are desirable in power systems when talking about the subject of "power quality.” Grounding affects voltage stability but, more importantly, is a critical element to personal safety. Harmonic currents are a mathematical model one often uses to analyze distorted waveforms flowing at higher frequencies than the common fundamental root frequency of 60 hertz.
The term "power harmonics” is probably familiar to most individuals involved in the electrical industry, but is probably more often misunderstood. Many technical articles and publications have been written about this subject, but these articles do not always address one’s basic problems and concerns in an understandable way. This article addresses the following questions.
- What are power system harmonics?
- What effect do they have on the power distribution system in a building?
- What are common symptoms or signs of harmonics or harmonic problems?
- How does one address these issues?
Harmonics is a mathematical model of the real world. Harmonics is simply a technique to analyze the current drawn by computers, electronic ballasts, variable frequency drives and other equipment which have modern "transformer-less” or electronic power supplies. These power supplies operate according to Ohm’s Law, which states that when a voltage is applied across a resistance, current will flow. This is how electrical equipment operates. Voltage applied across equipment is a sinewave which normally operates at 60 hertz (cycles per second) in the United States.
The utilities have the responsibility of generating this voltage at this 60-cycle sinewave. It has (relatively) constant amplitude and constant frequency.
Once this voltage is applied to any utilization equipment, Ohm’s Law is in effect. Ohm’s Law states that current equals voltage divided by resistance. The formula is simply:
I=E/R or Current (I) is equal to the Voltage (E)
divided by the Resistance (R)
Expressed graphically, the current ends up being another sinewave, since the resistance is a constant number. Ohm’s Law dictates that the frequency of the current wave is also 60 hertz. In the real world, this is true; although the two sinewaves may not align perfectly the current wave will indeed be a 60-cycle sinewave.
Fundamental Root Frequency 60 Hertz
Since an applied voltage sinewave will cause a sinusoidal current to be drawn, systems which exhibit this behavior are called linear systems. Incandescent lamps, heaters and, to a great extent, motors are linear systems.
Some modern equipment is taking on different characteristics. Computers, variable frequency drives (VFD’s), uninterruptable power supply systems and electronic ballasts are some types of non-linear electrical loads. In these systems, the resistance is not a constant and, in fact, varies during each sinewave. This occurs because the characteristics of the load drawn by the equipment are not a constant. The resistance, in fact, changes during each sinewave. The power supplies of these systems usually contain solid state devices such as power transistors, thyristors, or silicon-controlled rectifiers (SCRs). These devices draw current in pulses.
The major difference between an AC source and a DC switching power supply of most electronic equipment is simply that it draws current only within short periods of time or (cycles) within the normal sine wave. This is how harmonic currents are introduced into the return or neutral of an electrical power distribution system.
As voltage is applied to a solid state power supply, the current drawn is (approximately) zero until a critical "peak voltage” is reached on the sinewave. At this peak voltage, the transistor (or other device) gates or allows current to be conducted. This current typically increases over time until the peak of the sinewave and decreases until the critical peak voltage is reached on the "downward side” of the sinewave. The device then shuts off and current goes to zero. The same thing happens on the last 180° of the sinewave side with a second negative pulse of current being drawn. The resulting current is a series of positive and negative pulses, and not the true, smooth 60-cycle sinewave drawn by linear systems. Some systems have different shaped waveforms, such as square waves. These types of systems are often called non-linear systems. The power supplies which draw this type of current are called switched mode power supplies.
That is, one can create a series of sinewaves of varying frequencies and amplitudes to mathematically model this series of pulses. These are multiples of the fundamental frequency, 60 hertz. These multiple frequencies are called harmonics. The second harmonic would be two times 60 hertz,are called or 120 hertz. The third harmonic is 180 hertz and the fifth would be 300 hertz and on. In the typical three-phase power systems, the "even” harmonics (second, fourth, sixth, etc.) cancel. In these systems dealing with the "odd” harmonics is the challenge.
This figure shows the fundamental (60 Hz) and the third harmonic (180 Hz). As you can see, there are three cycles of the third harmonic for each single cycle of the fundamental. These two waveforms will be additive, as it flows it results in a non-sinusoidal waveform. Peaks will start forming that are indicative of the pulses drawn by switch mode power supplies. If one adds in other harmonics, one can model any distorted periodic waveform, such as square waves generated by UPS or VFD systems. It’s important to remember these harmonics are simply a mathematical model. The pulses or square waves, or other distorted waveforms are what one would actually see if one were to monitor an oscilloscope on the building’s wiring distribution systems. True RMS testing equipment is available and qualified testing facilities are available that can effectively measure these currents. These current pulses, because of Ohm’s Law, will also begin to distort the voltage waveforms in the building. This voltage distortion can cause premature failure of electronic devices.
On three-phase systems, the three phases of the power system are 120° out of phase. The current on phase B occurs 120° (1/3 cycle) after the current on A. The current on phase C occurs 120° after the current on phase B. Because of this, 60 hertz (fundamental) currents actually cancel on the neutral. If there are balanced 60 hertz currents on three-phase conductors, neutral current in theory and on the meters will be zero. It can be shown mathematically that the neutral current (assuming only 60 hertz is present) will never exceed the highest loaded phase conductor. Thus, overcurrent protection on phase conductors also protects the neutral conductor, even though there is no overcurrent protective device in the grounded or neutral conductor. This is in compliance with NEC® Section 240-22, which says one should not connect an overcurrent device in series with any grounded conductor of the system.
When harmonic currents are present, the third harmonic of each of the three-phase conductors is exactly in phase. When all of these harmonic currents return together on the neutral, rather than cancel, they actually add and can result in more current on the neutral conductor than on phase conductors. These neutral conductors, in effect, are no longer being protected against overcurrent by the overcurrent device (breaker or fuses) on the circuit. These harmonic currents will create heat, which, over a period of time, will raise the temperature of the neutral conductor. This temperature increase can overheat the associated conductors in the same enclosure and cause insulation failure. These harmonic currents also can cause sources (such as transformers or generators or converter windings) which supply the power system to overheat. This is the most obvious symptom of harmonics problems: overheating neutral conductors and transformers. This overheating is largely related to the "skin effect.” Simply stated: currents flowing at higher frequencies will not utilize the total conductor property or total circular mil area, but will flow on the skin of the conductor, creating heat. Some symptoms include:
- Heat in the conduit of wiring systems
- Computer malfunctions and data loss or errors
- Insulation degradation
- Nuisance tripping of circuit breakers
- Several solutions are available to address these symptoms:
Oversizing Neutral Conductors:
In three-phase circuits with shared neutrals, it is common to oversize the neutral conductor up to 200% when the load served consists of non-linear loads. For example, many panelboard manufacturers build a 200% neutral bus rated panelboard for these applications. Most manufacturers of office furniture systems provide a No.10 AWG conductor with 35 amp terminations for a neutral shared with the three No.12 AWG phase conductors. In feeders that have a large amount of non-linear load, the feeder neutral conductor and panelboard bus bar should also be oversized. Section 310-15(b)(4)(c) considers the neutral (that is carrying these types of currents as a majority of the load) current-carrying conductors.
Using Separate Neutral Conductors:
On three-phase branch circuits, another method, instead of installing a multiwire branch circuit sharing a neutral conductor, is to run separate neutral conductors for each phase conductor. This increases the capacity and ability of the branch circuits to handle these harmonic loads. While this successfully eliminates the addition of the harmonic currents on the branch circuit neutrals, the panelboard neutral bus and feeder neutral conductor still must be considered
Oversizing Transformers and Generators:
The oversizing of equipment for increased thermal capacity should also be used for transformers and generators which serve harmonics-producing loads. The larger equipment can dissipate more heat effectively.
Special transformers (K-Factor Transformers) are being manufactured to dissipate the additional heat caused by these harmonic currents. These transformers that are specifically designed to handle the effects of circuits and feeders with harmonic currents are being installed for old and new computer rooms and information technology systems.
Surge and Dip Filtering Equipment:
While many filters do not work particularly well at this frequency range, special electronic tracking filters can work very well to eliminate harmonics. These filters are presently relatively expensive but should be considered for thorough harmonic elimination.
Special Testing Equipment:
Standard clamp-on ammeters are only sensitive to 60 hertz current, so they only tell part of the story. New "true RMS” meters will sense current up to the kilohertz range. These meters should be used to detect harmonic currents. The difference between a reading on an old style clamp-on ammeter and a true RMS ammeter should give you an indication of the amount of harmonic current present.
Grounding Conductors: Your Safety Insurance Factor
Often times when the quality of the power is considered dirty, recommendations to install "isolated” equipment grounding conductors, also referred to as "separate grounds” or "clean grounds,” are the course of action. The rules for installing a separate isolated grounding conductor are covered in detail in the NEC® in Section 250-96(b) and 250-146(d) (See Figures 1 and 2 below). The Fine Print Note following each of these sections explains that the use of this method for the reduction of electrical noise in the grounding circuit does not relieve the requirement for grounding the raceway system and outlet box. The use of supplemental grounding electrodes often is in the plan for each electronic piece of equipment. While the National Electrical Code® allows this "supplemental electrode” in Section 250-54, it does not in any way relieve the requirement of the proper connection of an equipment-grounding conductor. "The earth shall not be used as the sole equipment grounding conductor.” Grounding conductors are required by the National Electrical Code® in the United States and by most other major electrical codes in the world. No matter what they are called, these conductors serve the same purpose. Grounding conductors connect all of the non-current carrying parts of the electrical system or any metallic parts in the vicinity of the electrical system together. This part includes conduits, enclosures, supports and other metallic objects. [See Figure 1 and Figure 2]
Example – Figure 1
Example – Figure 2
This grounding system has two purposes:
1. Safety. The grounding conductor system provides a low impedance path for fault currents to flow. This path must have three important characteristics. The path must be permanent and continuous, have lowest impedance possible, and the capacity to conduct safely any current imposed on it. This allows the full current to be detected by overcurrent protective devices (fuses and circuit breakers), safely clearing the fault, quickly eliminating shock hazards to persons and protecting property. See NEC® Section 250-2(d).
2. Power quality. The grounding system allows all equipment to have the same reference voltage. The electronic power supply in electronic equipment uses the frame of the equipment for the reference point. This is where the ac equipment grounding conductor and the electronic equipment grounding circuit come together. (See figure below.) This helps the facility’s electronic equipment operation and helps prevent the flowing of objectionable currents on communication lines, conduits, shields, and other connections.
To examine the safety issue more closely, consider the following system: a power system consisting of a voltage source (transformer or generator) connected to a disconnect and a panelboard. An appliance is fed from this panelboard. When the circuit is formed current flows in the circuit allowing the appliance to operate. The grounding conductor connects the frame of the appliance to the panelboard enclosure and to the service enclosure. This enclosure is connected to the grounded conductor (often the neutral conductor) which, in turn, is connected to the grounded terminal of the transformer. If a ground-fault occurs, the grounding conductor connection allows current to flow. This current will be much greater than the normal load current and will cause the circuit breaker to open quickly. This safely clears the fault and minimizes any safety hazard to personnel. Suppose the grounding conductor is not connected properly or is interrupted. If a fault occurs, little or no current will flow in the grounding conductor since the circuit is interrupted. This opened grounding conductor could be caused by a grounding prong illegally cut off a cord cap, a loose connection, a conduit which is not connected properly or many other causes. This fault leaves the frame of the appliance energized. Should someone touch both the appliance and the building steel, another piping system, or possibly even a wet concrete floor, the circuit would then be completed in current flow through the body, injuring or killing the person. The National Electrical Code® recognizes the use of certain raceways and cables as equipment grounding conductors. Many designers today do not believe that using steel conduits is adequate for this use. Conduit has connections every ten feet and often low-grade, cast-metal couplings and connectors are used. The secondary benefit of this copper grounding conductor is it will provide an equipotential plane for all equipment connected to it. This often makes the so-called isolated grounding conductors specified by computer and other manufacturers unnecessary.
Article 250 of the National Electrical Code® sets up the minimum requirements for grounding and bonding of electrical power distribution systems. Article 250 took on a new look and feel for the 1999 Code cycle. First, it should be understood that all of the previous requirements in Article 250 are still in place as minimum requirements. Second, the article has been totally reorganized. The performance based requirements in 1996 Section 250-1 FPN 1 & 2 and also Section 250-51 have been written into the general requirements of Part A. The 1999 edition also continued its quest to migrate away from using the grounded conductor for grounding equipment downstream of a main bonding jumper at a service, or downstream from a bonding jumper at a separately derived system. This still is allowable in very few cases with several restrictions. The section on objectionable current flowing on the grounding system still exists in Article 250. It is worth a closer look. Section 250-6(d) deals with permissible alterations to stop objectionable current. This section explains that the provisions of this section should not be misunderstood as allowing electronic equipment from being operated on ac systems that are not grounded as required by Article 250.
Following the minimum requirements in the National Electrical Code® essentially provides for the safety aspect and purpose of chapter two (Wiring and Protection). By following the rules in Article 250 regarding properly sized grounding conductors, proper use of isolated grounding conductors, code compliant installation of supplemental grounding electrodes, and proper connections of both grounded conductors and equipment grounding conductors users can ultimately end up with one having the”best of both worlds” when it comes to power quality issues and most important safety concerns. These grounding and bonding topics are extensively covered in the IAEI Soares Book on Grounding (Seventh Edition).
Read more by Michael Johnston
Posted By George Anchales,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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Improper maintenance, the aging process of time, and corrosion plus the lack of a ground-fault circuit-interrupter (GFCI), a device that prevents electrocution, has made underwater swimming pool light fixtures installed prior to the enforcement of the 1975 National Electrical Code (NEC®) a potential source for electrocution.
Figure 1. This flush deck junction box serves an underwater light fixture. Flush desk boxes have been allowed sincet he 1971 NEC only on lighting systems of 15 volts or less and when filled with an approved potting compound and located not less than 4 feet from the inside wall of the pool.
Figure 2. This flush desk box is too close to the inside wall of the pool (4 feet minimum distance required).
This hazard, however, may be eliminated by proper maintenance and the installation of a new light fixture protected by a GFCI device.
In recent years, California has been the site of several unfortunate and unnecessary deaths due to electrocution by these obsolete installations. These deaths could have been prevented by 1) notifying the public through newspapers, radio, television and posted bulletins of the potential hazards; 2) advising the public through the same channels of the steps to remedy the problem; 3) requiring permits to be issued for the corrective work; and 4) requiring proper inspection to insure that the corrections meet NEC® requirements.
The NEC® did not address swimming pools until 1962, when "Article 680 – Swimming Pools,” first appeared in the Code. From 1962 until the 1975 edition of the NEC®, GFCI protection was only optional. The 1962 NEC® Section 680-2(g) read as follows:
"All circuits supplying underwater fixtures should be isolated. If the circuit voltage is greater than 30 volts, an approved fail-safe ground detector device which automatically de-energizes the circuit or an approved grid structure or similar safeguard should be used.”
Consequently, thousands of swimming pool underwater light fixtures were installed without GFCI protection. After years of exposure to chlorinated water, serious hazards now exist.
The 1975 NEC® was the first to mandate GFCI protection for underwater light fixtures operating at more than 15 volts. The 1975 NEC® Section 680-20(a)(1) stated:
"In addition, a ground-fault circuit-interrupter shall be installed in the branch circuit supplying fixtures operating at more than 15 volts, so that there is no shock hazard during relamping. The installation of the ground-fault circuit-interrupter shall be such that there is no shock hazard with any likely fault-condition combination that involves a person in a conductive path from any ungrounded part of the branch circuit or the fixture to be grounded.”
All editions of the NEC® since 1975 have this GFCI requirement.
The following illustrations show examples of these early installations.
Figures 1 and 2 show a flush deck junction box that serves an underwater light fixture. Flush deck boxes have been allowed since the 1971 NEC® only on lighting systems of 115 volts or less and when filled with an approved potting compound and located not less than 4 feet from the inside wall of the pool.
Many of these early flush deck boxes lack the above requirements and as the two deck boxes in Figures 3 and 4 illustrate, pose hazards. These hazards include deteriorated boxes, cover gaskets, and conductors. Figure 4 also illustrates a deck box being used as a junction box for a circuit supplying a garage subpanel.
Circuits supplying underwater fixtures have been required to be isolated since the 1962 Code (see above) but as illustrated in Figures 4, 5 and 6 many boxes and enclosures serving underwater light fixtures are being used as junction boxes for circuits supplying other pieces of equipment (i.e., timers, deck lights and garage circuits). This wiring method has been a violation of the Code since the 1962 edition of the NEC®
In 1968, the NEC® first required encapsulating the flexible cord conductor terminations within the light fixture. Section 680-4(1) reads as follows:
"The end of the flexible cord conductor terminations within a fixture shall be covered with or encapsulated in a suitable potting compound to prevent the entry of water into the fixture through the cord or its conductors. In addition, the grounding connection within a fixture shall be similarly treated to protect such connection from the deteriorating effect of pool water in the event of water entry into the fixture.”
As Figures 7 and 8 show, there are light fixtures installed which do not afford this added protection.
These obsolete fixtures will also trip today’s GFCI devices because they leak too much current. Because of these facts, you must install both a new light fixture and a GFCI device. This combination will eliminate the shock hazard that exists with these earlier installations.
One additional hazard that should be mentioned is non-GFCI protected, 125-volt receptacles located within 20 feet of the inside walls of pools. These receptacles should also be protected by a GFCI device.
GFCI protection for receptacles located between 10 and 15 feet of the pool was first required in the 1971 NEC®. Since the 1984 NEC®, that distance was extended to include all 125-volt receptacles within 20 feet of the pool.
The hazards discussed in this article may be eliminated by proper maintenance and the installation of a new light fixture protected by a GFCI device. GFCI protection should also be provided for all 125-volt receptacles within 20 feet of the pool.
Unless additional corrective measures are necessary, the estimated cost for labor and materials is $500. This is a small price to pay to protect against the further loss of life.
Read more by George Anchales
Posted By Michael Callanan,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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More than likely, however, in our industry, what we do know about electricity will cause more damage. Although armed with knowledge, we tend to forget the precautions and get caught up in the excitement of electricity.
What you don’t knowabout Electricity could hurt you and your family…
More than likely, however, in our industry, what wedo knowabout electricity will cause more damage.
Although armed with knowledge, we tend to forget the precautions and get caught up in the excitement of electricity, as Icarus was captivated by the thrill of flight. Long ago he and his father, Daedalus, were imprisoned on the island of Crete, with no hope of escape. Not wishing his only son to face this terrible ordeal, Daedalus made artificial wings. Warning his son not to fly too close to the sun lest the wax melt, Daedalus and Icarus soared off the island, discovering the excitement and thrill of flight. In his ecstasy, Icarus forgot his father’s warnings and flew farther and higher, until the sun melted the wax and, tragically, he plunged into the Aegean sea.
Each of us can relate horrible, tragic tales of those who have dared to draw too close to Electricity, those who have paid the ultimate price for her intimacy.
Though an exciting, appealing and awe-inspiring temptress, Electricity has no favored ones. She strikes furiously at those who, in familiarity, presume to live on the edge or push to the extreme and who handle her carelessly.
Electrical Systems Need Inspection
Consumer Product Safety Commission studies of residential electrical fires show that the majority of serious fires need not have occurred. The conditions that caused the fires probably would have been detected by an electrical inspection. These problems were not detected or corrected because no inspection had been made for several years. In a number of cases investigated by CPSC, homes ranging from 40 to 100 years old had not been inspected since they were built. A safety inspection should be performed by a qualified electrical or licensed electrical inspector.
To insure the electrical safety of your home, your electrical inspection should be up-to-date and defects corrected. There are no hard-and-fast rules about frequency of inspection but here are some suggestions:
To determine when your electrical system was last inspected, examine the door and cover of your electrical panel(s). The panel should contain a label or tag with a date, a signature, or initials on it. If there is more than one date, the most recent one should be the date of the last inspection. DO NOT remove the service-panel cover. This is a job for a qualified electrician.
|POWER OUTAGES||fuses need replacement or circuit breakers need resetting frequently|
|OVERRATED PANEL||electrical panel contains fuses or circuit breakers rated as higher currents than the ampacity (current capacity) of their branch circuits, sometimes called "overamped” or "overfused”|
|DIM/FLICKERING LIGHTS||lights dim or the size of your television picture shrinks often|
|ARCS/SPARKS||bright light flashes or showers of sparks anywhere in your electrical system|
|SIZZLES/BUZZES||unusual sounds from the electrical system|
Problems with Home Electrical Wiring
Each year many Americans are injured in and around their homes. Unsafe conditions such as overloaded circuits and damaged insulation as well as the misuse of extension cords and electrical products create fire hazards and may result in electrocutions.
The most recent U.S. Consumer Product Safety Commission statistics show that 40,000 fires a year are caused by problems with home electrical wiring, resulting in one life being lost every 25 hours (over 350 fires lost annually), approximately 6,800 injuries and over 2 billion in property damage.1Workplace statistics show one person is electrocuted in the workplace every day2; and millions of dollars are lost in corporate and personal productivity and assets because of related litigation.
Take a few minutes to look for and correct electrical safety hazards in your home. It does not take too long to check the insulation on a cord, move an appliance away from water, check for correct wattage light bulbs or install a GFCI (Ground Fault Circuit Interrupter).
Invest your time. It could prevent an electrical safety hazard and save lives.
1CPSC, May 22, 1996 2 OSHA
If your last inspection was…
- 40 or more years ago, inspection is overdue
- 10-40 years ago, inspection is advisable, especially if substantial electrical loads (high-wattage appliances, lights and wall outlets or extension cords) have been added or if some of the warning signs discussed are present.
- Less than 10 years ago, inspection may not be needed, unless some of the warning signs, described are present or temporary wiring has been added.
- You may live in an area that is not served by state or local electrical inspectors, so that no inspection record will be found on your electrical panel. In that case, use the age of the house as a guide to the probable need for an inspection.
Q. Are the light bulbs the appropriate size and type for the lamp or fixture?
A bulb of too high wattage or the wrong type may lead to fire through overheating. Ceiling fixtures, recessed lights, and "hooded” lamps will trap heat.
Replace with a bulb of the correct type and wattage. (If you do not know the correct wattage, contact the manufacturer of the fixture.)
Place halogen lamps away from curtains. These lamps become very hot and can cause a fire hazard.
Appliance Power Budget
Circuits can only handle a specifiedtotalwattage of all the electrical products connected to that circuit. If too much wattage is plugged into a circuit, serious electrical problems can result. Here is a guide to knowing what a circuit can handle:
|5-ampere branch circuit can carry 1500 watts.20-ampere branch circuit can carry 2000 watts.|
Find the nameplate on each appliance indicating its power (watts) rating. Add up the total watts for appliances that you may use at the same time on the same branch circuit. Examples:
|Hair Dryer||1400 watts|
|Portable Heater||1200 watts|
|Vacuum Cleaner||1300 watts|
|Deep Fat Fryer||1300 watts|
|Portable Fan||150 watts|
Most home lighting and wall outlet branch circuits may carry as much as 1500 watts (15ampere branch); some kitchen circuits, as much as 2000 watts (20 ampere).
A ground-fault circuit interrupter (GFCI) detects any loss (leakage) of electrical current in a circuit that might be flowing through a person using an electrical product. When such a loss is detected, the GFCI turns electricity off before severe injuries or electrocution can occur. (However, you may receive a painful shock during the time that it takes for the GFCI to cut off the electricity.)
GFCI wall outlets can be installed in place of standard outlets to protect against electrocution for just that outlet, or a series of outlets in the same branch.
A GFCI circuit breaker can be installed on some circuit breaker electrical panels to protect against electrocution, excessive leakage current and overcurrent for an entire branch circuit.
Plug-in GFCIs can be plugged into wall outlets where appliances will be used.
Q. Have you tested your GFCIs to be sure they still offers protection from fatal electrical shock?oYesoNo
A GFCI can provide power without giving an indication that it is no longer providing shock protection. Be sure your GFCI still provides protection from fatal electric shock.
- Test monthly. First plug a night light or lamp into the GFCI-protected wall outlet (the light should be turned on), then depress the "TEST” button on the GFCI. If the GFCI is working properly, the light should go out. There will be an indicator to show if it is working properly or not. If it is working, it will disconnect the power from the protected circuit or plug. If not, have the GFCI replaced. Reset the GFCI to restore power.
- If the "RESET” button pops out but the light does not go out, the GFCI has been improperly wired and does not offer shock protection at that wall outlet. Contact a qualified electrician to correct any wiring errors.
PROBLEM: Electric shocks can be more serious in certain locations of the home such as bathrooms, kitchens, basements and garages where people can contact heating radiators, water pipes, electric heaters, electric stoves and water in sinks and bathtubs. If a person touches one of these and a faulty electrical appliance at the same time, they can receive a shock and may be electrocuted.
- If you have a home without GFCIs, consult with a qualified electrician about adding this protection.
- If you want to install some GFCI protection yourself, use plug-in units to protect individual wall outlets. Both two-conductor and three-conductor receptacle outlets can be protected with plug-in units.
- You may have a newer home that is equipped with GFCIs in the home areas mentioned above.
Rated for 1625 Watts
Change the cord to a higher rated one or unplug some appliances, if the rating on the cord is exceeded because of the power requirements of one or more appliances being used on the cord.
- Use an extension cord having a sufficient amp or wattage rating, if an extension cord is needed.
Q. Do extension cords carry no more than their proper load, as indicated by the ratings labeled on the cord and the appliance?
Overloaded extension cords may cause fires.
- Replace No. 18 gauge cords with No. 16 gauge cords. Older extension cords using small (No. 18 gauge) wires can overheat at 15 amps or 20 amps.
Receptacle Outlets and Switches
Q.Do all outlets and switches have cover plates so that no wiring is exposed?
Exposed wiring presents a shock hazard.
Add a cover plate.
Q. Are small electrical appliances such as hair dryers, shavers, curling irons, unplugged when not in use?
Small Appliances and Tools
Even an appliance that is not turned on, such as a hairdryer, can be potentially hazardous if it is left plugged in. If it falls into water in a sink or bathtub while plugged in, it could electrocute you.
Install ground fault circuit interrupter (GFCI) protection near your kitchen and bathroom sinks to protect against electric shock. For more information, see the section on GFCIs.
Unplug all small appliances when not in use.
Never reach into water to get an appliance that has fallen in without being sure the appliance is unplugged
Q. Do you make sure that there is nothing covering your electric blanket when in use, and do you avoid "tucking in” the sides or ends of your electric blanket?
o Yes o No
"Tucking in” an electric blanket or placing additional coverings on top of it can cause excessive heat buildup which can start a fire.
Do not tuck in electric blankets.
Use electric blankets according to the manufacturer’s instructions.
Don’t allow anything on top of the blanket while it is in use. (This includes other blankets or comforters, even pets sleeping on top of the blanket.)
Do not use electric blankets on children.
Q. Are lamp, extension, telephone and other cords placed out of the flow of traffic?oYesoNo
Cords stretched across walkways may cause someone to trip.
Whenever possible, arrange furniture so that outlets are available for lamps and appliances without the use of extension cords. Extension cords should not be used as a substitute for permanent wiring.
- If you must use an extension cord, place it on the floor against a wall where people cannot trip over it.
- Move the phone so that telephone cords will not lie where people walk.
Q. Are cords out from beneath furniture and rugs or carpeting?oYesoNo
Furniture resting on cords can damage them. Electric cords which run under carpeting can overheat and cause a fire.
Remove cords from under furniture or carpeting. Replace damaged or frayed cords.
Q. Are cords attached to the walls, baseboards, etc. with nails or staples?
o Yes o No
Nails or staples can damage cords, presenting fire and shock hazards.
- Remove nails and staples from cords after disconnecting power.
- Check wiring for damage.
- Use tape if necessary to attach cords to walls or floors.
Q. Are electrical cords in good condition, not frayed or cracked?
o Yes o No
Damaged cords may cause a shock or fire.
- Replace frayed or cracked cords.
- Do not use frayed electrical cords
The National Electrical Safety Foundation established in July 1994 as a publicly organized charitable organization, is dedicated to the mission of building public awareness about the importance of respecting electricity and using electrical products safely in the home, school and workplace.
To contribute to this effort, contact NESF at 703-841-3211.
Copyright © 1999 by NESF. Reprinted with permission.
Read more by Michael Callanan
Posted By Robert Milatovich ,
Monday, March 01, 1999
Updated: Monday, August 27, 2012
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First a little history of the National Electrical Code (NEC) dealing with the title of Article 680 and the addition of Part E. Fountains. The title of Article 680 in the 1962 NEC was "Swimming Pools” and remained that until the 1971 NEC when the title was changed to "Swimming and Wading Pools.” Then in the 1975 NEC the title was changed to "Swimming Pools, Fountains and Similar Installations.” Fountains were added to Article 680 as Part D. In the 1981 NEC Article 680, Part D was changed to Part E of Article 680, with the section numbers being changed from Section 680-40’s to 680-50’s.
Photo 1. Permanent Fountain
Photo 2. Permanent Fountain
In the next few pages I will try to dissect Article 680, Part E. Fountains, to explain what it means and how I think it should be interpreted. I hope this will be of some value to you.
My comments are not the official interpretations of the 1999 National Electrical Code (NFPA 70) published by the National Fire Protection Association.
Part E. Fountains
680-50. General.The provisions of Part E shall apply to all permanently installed fountains as defined in Section 680-4. Self-contained, portable fountains no larger than 5 ft (1.52 m) in any dimension are not covered by Part E. Fountains that have water common to a pool shall comply with the pool requirements of this article.
[See photos 1, 2, 3, and 4].
Photo 3. The fountain in this picture is what is referred to as a self-contained, portable fountain no larger than 5 ft. in any dimension
Starting with Section 680-50. General, the provisions of Part E shall apply to all permanently installed fountains as defined in Section 680-4.
In the 1981 NEC the word "include” and the words "fountain, fountain pools, ornamental display pools, and reflection pools” were removed and the words "”shall apply to all fountains as defined in Section 680-1″ were added.
In the 1984 NEC the reference to "Section 680-1″ was changed to "Section 680-4.” The words "permanently installed” were added to the 1999 edition of the NEC.
When we look at 680-4. Definitions, we find the following definition: "Fountain. As used in this article, the term includes fountains, ornamental pools, display pools, and reflection pools. It does not include drinking fountains.” This new definition was added for the 1999 NEC.
Photo 4. Swimming pool with a fountain using the same water
This definition was the second sentence in Section 680-1. Scope. (FPN) of the 1996 NEC®, which read, "The term fountain as used in the balance of this article includes fountains, ornamental pools, display pools, and reflection pools. The term is not intended to include drinking water fountains.” The words "includes fountains, ornamental pools, display pools, and reflection pools” has been in this Section since the 1975 NEC.
The Section continues with "self-contained, portable fountains no larger than 5 ft. (1.52 m) in any dimension are not covered by Part E.” This was an exception to Section 680-1 in the 1978 NEC and remained an exception until the 1999 NEC.
The last sentence informs us that fountains that have water common to a pool shall comply with the pool requirements of this article. This sentence has been inSection 680-1. Scope.from the first time it appeared in the 1975 NEC.
Photo 5. Transformer meeting the requirements of Section 680-51
680-51. Lighting Fixtures, Submersible Pumps, and Other Submersible Equipment.
This Section has not changed since it was introduced in the 1975 NEC. [See photo 5]
(a) Ground-Fault Circuit-Interrupter.A ground-fault circuit-interrupter shall be installed in the branch circuit supplying fountain equipment unless the equipment is listed for operation at 15 volts or less and supplied by a transformer that complies with Section 680-5(a).
Subsection (a) was in the 1975 NEC when fountains were added to the NEC and informs us that a ground-fault circuit-interrupter (GFCI) shall be installed in the branch circuit supplying fountain equipment, (the remainder of this sentence was an exception until the 1999 NEC) unless the equipment is listed for operation at 15 volts or less and supplied by a transformer that complies with Section 680-5(a).
Photo 6. Underwater fixture with a guarded lens
When we look at Section 680-5, Transformers and Ground-Fault Circuit-Interrupter, in subsection (a) we find the requirements for transformers which states, "Transformers used for the supply of underwater fixtures, together with the transformer enclosure, shall be identified for the purpose. The transformer shall be an isolated winding type having a grounded metal barrier between the primary and secondary windings.”
(b) Operating Voltage.No lighting fixtures shall be installed for operation on supply circuits over 150 volts between conductors. Submersible pumps and other submersible equipment shall operate at 300 volts or less between conductors.
Subsection (b) was in the original submission for fountains in the 1975 NEC, and the first word in this paragraph was "No.”
In the 1981 NEC it was changed to "All.”
In the 1999 NEC it was changed back to "No.”
In the 1975 NEC the word "”at”" was placed before the word "over,” the words "circuits supplying” were placed in the second sentence and then were removed in the 1981 NEC. The words "not to exceed” were added before the words "300 volts” and the words "or less” were added after the words "300 volts” and removed in the 1981 NEC.
In the 1981 NEC the words "or less” were placed after the words "150 volts.”
Subsection (b) Operating Voltage,informs us that no lighting fixtures shall be installed for operation on supply circuits over 150 volts between conductors. (This would mean that the voltage between any conductors, be it two hot conductors, or a hot conductor and a grounded
Photo 7. Underwater fixture with a low-water cutoff
conductor, shall not have a voltage of over 150 volts. You can also find this requirement in Part B, Permanently Installed Pools, 680-20(a), General, Subsection 2). Submersible pumps and other submersible equipment shall operate at 300 volts or less between conductors. (This would mean that the voltage between any conductors, be it two hot conductors, or a hot conductor and a grounded conductor, shall not have a voltage of over 300 volts for submersible equipment.)
(c) Lighting Fixture Lenses.Lighting fixtures shall be installed with the top of the fixture lens below the normal water level of the fountain unless approved for above-water locations. A lighting fixture facing upward shall have the lens adequately guarded to prevent contact by any person.
Photo 8. Underwater fixture
Subsection (c) has remained the same since the addition in the 1975 NEC. [See photos 6, 7, and 8]
(d) Overheating Protection.Electric equipment that depends on submersion for safe operation shall be protected against overheating by a low-water cutoff or other approved means when not submerged.
In the 1993 NEC, in Subsection (d) the word "which” after the words "Electrical equipment” was changed to the word "that.”"
(e) Wiring.Equipment shall be equipped with provisions for threaded conduit entries or be provided with a suitable flexible cord. The maximum length of exposed cord in the fountain shall be limited to 10 ft. (3.05 m). Cords extending beyond the fountain perimeter shall be enclosed in approved wiring enclosures. Metal parts of equipment in contact with water shall be of brass or other approved corrosion-resistant metal.
Subsection (e) has remained the same since the 1975 edition of the NEC.
Subsection (e), Wiring, informs us that all electrical equipment shall be equipped with provisions for threaded conduit entries or be provided with a suitable flexible cord. The maximum length of exposed cord in the fountain shall be limited to 10 ft. (3.05 m) and cords extending beyond the fountain perimeter shall be enclosed in approved wiring enclosures. Metal parts of equipment in contact with water shall be of brass or other approved corrosion-resistant metal.
(f) Servicing.All equipment shall be removable from the water for relamping or normal maintenance. Fixtures shall not be permanently imbedded into the fountain structure so that the water level must be reduced or the fountain drained for relamping, maintenance, or inspection.
Subsection (f) has remained the same since the 1975 edition of the NEC.
Subsection (f) Servicing, informs us that all equipment installed in a fountain shall be removable from the water for relamping or normal maintenance. Lighting fixtures shall not be placed into the walls, the bottom, or permanently imbedded into the fountain structure so that the water level must be reduced or the fountain drained for relamping, maintenance, or inspection.
(g) Stability.Equipment shall be inherently stable or be securely fastened in place.
Subsection (g) has remained the same since the 1975 edition of the NEC.
Photo 10. Underwater junction box
Subsection (g) Stability, informs us that equipment shall be inherently stable or be securely fastened in place. Placing a fixture on its side, when it is designed to sit on the bottom of the fountain facing in the up direction would not be inherently stable.
680-52. Junction Boxes and Other Enclosures.
This Section has changed very little since it was introduced in the 1975 NEC. [See photos 9 and 10]
(a) General.Junction boxes and other enclosures used for other than underwater installation shall comply with Sections 680-21(a), (b), (c), (d) and (e).
Subsection (a) is the same as the 1975 edition of the NEC® with the exception of the requirements in Section 680-21(a), which originally told us that only (a) 1, 2 and 3 would apply to fountains which has remained the same until the 1999 NEC.
Subsection (a) informs us that all junction boxes and other enclosures used for other than underwater installation shall comply with the requirements of Sections 680-21(a), (b), (c), (d) and (e) which refers to "Junction Boxes and Enclosures for Transformers or Ground-Fault Circuit-Interrupters.”"
(b) Underwater Junction Boxes and Other Underwater Enclosures.Junction boxes and other underwater enclosures shall be submersible and:
(1) be equipped with provisions for threaded conduit entries or compression glands or seals for cord entry;
(2) be of copper, brass, or other approved corrosion-resistant material;
(3) be filled with an approved potting compound to prevent the entry of moisture; and
(4) be firmly attached to the supports or directly to the fountain surface and bonded as required.
Where the junction box is supported only by the conduit, the conduit shall be of copper, brass, or other approved corrosion-resistant metal. Where the box is fed by nonmetallic conduit, it shall have additional supports and fasteners of copper, brass, or other approved corrosion-resistant material.
Section 680-21(b) in the 1975 NEC stated, "Junction boxes and other underwater enclosures immersed in water or exposed to water spray shall comply with the following…”
In the 1981 NEC this was rewritten and the words, "immersed in water or exposed to water spray shall comply with the following…” were replaced with "shall be watertight…”
Photo 11. Sign in fountain
In the 1987 NEC the word "watertight” was changed to "submersible”"and Section 680-21(b)(3) was changed from "”shall be located below the water level in the fountain wall or floor. An approved potting compound shall be used to fill the box to prevent the entry of moisture; and…” to "be filled with an approved potting compound to prevent the entry of moisture; and…”
In the 1981 NEC Section 680-21(b)(4), the structure of the paragraph was changed by taking the first sentence and making it a paragraph under (b)(4), but not part of (b)(4) and rewording the last sentence by removing the first three words "The box must…”
Section 680-21(b), Underwater Junction Boxes and Other Underwater Enclosures, informs us that all junction boxes and other underwater enclosures shall be listed as submersible and;
(1) be equipped with provisions for threaded conduit entries, such as hubs, or a type of compression gland or seals used for cord entry;
(2) be of copper, brass, or other approved corrosion-resistant material;
(3) be filled with an approved potting compound (See U.L. Standard 746A and 746C) to prevent the entry of moisture into the enclosures; and
(4) be firmly attached to the supports or directly to the fountain surface and bonded as required.
Where the junction box is supported only by the conduit, (we have to look at Section 370-23(e) and (f) which states, an enclosure supported by a raceway shall not exceed 100 cubic inches in size, have threaded entries or hubs, and be supported by two or more conduits secured with 18 inches of the enclosure, the conduit shall be of copper, brass, or other approved corrosion-resistant metal. (This would not include conduits with a galvanized finish such as rigid metal or intermediate metal conduit.) Where the box is fed by nonmetallic conduit, it shall have additional supports and fasteners of copper, brass, or other approved corrosion-resistant material. (This would not include supports and fasteners with a galvanized finish.)
FPN: See Section 370-23 for support of enclosures.
This FPN tells us to look at Article 370, Outlet, Device, Pull and Junction Boxes, Conduit Bodies and Fittings; Section 370-23, Supports, which tells us how the enclosures are to be supported.
Section 680-53, Bonding, all metal piping systems associated with the fountain shall be bonded to the equipment grounding conductor of the branch circuit supplying the fountain.
In the 1975 NEC this Section was worded, "All metallic piping systems associated with the fountain shall be bonded to the electrical system ground as required in Article 250,” and a new FPN appeared as "See Section 250-95 for sizing of these conductors.”
In the 1987 NEC the word "metallic” was changed to "metal” and remains the same in the 1999 NEC.
In the 1999 NEC the words "electrical system ground as required in Article 250,” were replaced with the words "equipment grounding conductor of the branch circuit supplying the fountain,” and FPN was changed to "See Section 250-122 for sizing of these conductors.”
FPN: See Section 250-122 for sizing of these conductors.
In the 1975 NEC a new FPN appeared as "See Section 250-95 for sizing of these conductors.”
In the 1999 NEC the FPN was changed to "See Section 250-122 for sizing of these conductors.”
This FPN tells us to look at Section 250-122, Size of Equipment Grounding Conductors. This section tells us that the size of the equipment grounding conductor is sized for the Rating or Setting of the Overcurrent Device for that circuit.
Section 680-54, Grounding. The following equipment shall be grounded:
(1) all electric equipment located within the fountain or within 5 ft. (1.52 m) of the inside wall of the fountain
(2) all electric equipment associated with the recirculating system of the fountain
(3) panelboards that are not part of the service equipment and that supply any electric equipment associated with the fountain.
In the 1987 NEC®, in subsection (1) the words "located within the fountain or” were added after the words "all electric equipment.”
680-55. Methods of Grounding.
(a) Applied Provisions. The provisions of Section 680-25 shall apply, excluding paragraph (e).
In the 1981 NEC (a) added a heading, "Applied Provisions,” and the words "Paragraph (a) and (d) excluding Exception 3,” after the word "apply” was changed to "Paragraph (a) and (c) excluding Exceptions.”
In the 1984 NEC it was changed again to "excluding paragraph (e).”
In the 1999 NEC the word "following” was deleted before the word "provisions.”
Section 680-55(a) informs us to look at Section 680-25, Methods of Grounding, and we see that it shall apply to all fountains with the exception of (e) Cord-Connected Equipment, which shall not apply to fountains.
Section 680-55(b), Supplied by a Flexible Cord, electric equipment that is supplied by a flexible cord shall have all exposed noncurrent-carrying metal parts grounded by an insulated copper equipment grounding conductor that is an integral part of this cord. This grounding conductor shall be connected to a grounding terminal in the supply junction box, transformer enclosure, or other enclosure.
Subsection (b) has remained the same since the 1975 NEC with the exception of a new heading in the 1981 NEC "(b) Supplied by a Flexible Cord.”
Subsection (b) informs us that all electric equipment that is supplied by a flexible cord shall have all exposed noncurrent-carrying metal parts grounded by an insulated copper equipment grounding conductor and this grounding conductor shall be an integral part of this cord. This equipment grounding conductor shall be connected to a grounding terminal that is required in Section 680-21(d), Grounding Terminals, which requires that a number of grounding terminals shall be at least one more than the number of conduit entries in the supply junction box, transformer enclosure, or other enclosure.
680-56. Cord- and Plug-Connected Equipment.
(a) Ground-Fault Circuit-Interrupter. All electric equipment, including power-supply cords, shall be protected by ground-fault circuit-interrupters.
Subsection (a) has remained the same since the 1975 NEC.
Subsection (a) informs us that all cord- and plug-connected electric equipment, including power-supply cords, shall be protected by ground-fault circuit-interrupters (GFCI).
(b) Cord Type. Flexible cord immersed in or exposed to water shall be of the hard-service type as designated in Table 400-4 and shall be marked water resistant.
In the 1975 NEC, after the words "shall be” were the words "a water-resistant Type SO or ST.”
In the 1990 NEC the words "marked water-resistant” were added after the words "Type SO or ST.”
In the 1993 NEC the text was changed to the present wording by adding "of the hard-service type as designated in Table 400-4 and shall be marked water resistant” after the words "shall be.”
Subsection (b) informs us that all flexible cord immersed in or exposed to water in a fountain shall be of the hard-service type as designated in Table 400-4, Flexible Cords and Cables, and shall be marked water resistant.
(c) Sealing. The end of the flexible cord jacket and the flexible cord conductor termination within equipment shall be covered with, or encapsulated in, a suitable potting compound to prevent the entry of water into the equipment through the cord or its conductors. In addition, the ground connection within equipment shall be similarly treated to protect such connections from the deteriorating effect of water that may enter into the equipment.
Subsection (c) has remained the same since the 1975 NEC with the exception that the word "which” after the word "”water”" in the last sentence was changed to "that” in the 1993 NEC.
Subsection (c) informs us that the end of the flexible cord jacket and the flexible cord conductor termination within equipment shall be (sealed) covered with, or encapsulated in, a suitable potting compound to prevent the entry of water into the equipment through the cord or its conductors. In addition, the equipment ground connection within equipment shall be similarly (sealed) covered with, or encapsulated in, a suitable potting compound and treated to protect such connections from the deteriorating effect of water that may enter into the equipment.
(d) Terminations. Connections with flexible cord shall be permanent, except that grounding-type attachment plugs and receptacles shall be permitted to facilitate removal or disconnection for maintenance, repair, or storage of fixed or stationary equipment not located in any water-containing part of a fountain.
Subsection (d) has remained the same since the 1975 NEC, except for the deletion of the words "or pool” in the 1981 NEC.
Subsection (d) informs us that the connections with flexible cord shall be permanent for all cord-connected equipment located in any water-containing part of a fountain.
Fixed or stationary equipment not located in any water-containing part of a fountain which uses grounding-type attachment plugs and receptacles to facilitate removal or disconnection for maintenance, repair, or storage.
In the 1975 NEC there was a "Section 680-47. Equipment Rooms.”
In the 1981 NEC this was moved to "680-11. Equipment Rooms. Electric equipment shall not be installed in rooms which do not have adequate drainage to prevent water accumulation during normal operation or filter maintenance.”"
In the 1984 NEC the words "and Pits” were added to the heading of "Section 680-11″ and after the word "rooms” and remains the same in the 1999 NEC.
Sign in a Fountain
This Section is new for the 1999 NEC because of the increasing use of advertising signs being installed inside of or being part of the fountains. [See photo 11]
(a) General. Includes only fixed, stationary electrically illuminated utilization equipment with words or symbols designed to convey information or attract attention.
Subsection (a) identifies what is covered by Section 680-57. If we look at Article 100, Definitions, you will see: "Electric Sign: A fixed, stationary, or portable self-contained, electrically illuminated utilization equipment with words or symbols designed to convey information or attract attention.” As you can see the definition of an electric sign contains the words "portable self-contained” which are not part of this requirement.
(b) Ground-Fault Circuit-Interrupter Protection for Personnel. All feeders or circuits shall be protected by ground-fault circuit-interrupters protection for personnel.
Subsection (b) informs us that all feeders or circuits supplying a sign installed in a fountain shall be protected by ground-fault circuit-interrupters (GFCI) protection for personnel, which means that the ground-fault circuit-interrupters (GFCI) are to be a Class A type, with a ground fault trip threshold of 6mA maximum.
(c) Location. Any sign installed inside a fountain shall be at least 5 feet inside the fountain measured from the outside edges of the fountain.
Subsection (c) informs us that any sign installed inside of a fountain shall be at least 5 feet inside of the fountain and that this is to be measured from the outside edges of the fountain to any part of the sign or sign structure.
(d) Disconnect. Shall comply with 600-6.
Subsection (d) informs us that the disconnect shall comply with Article 600. Electric Signs and Outline Lighting, Section 600-6 Disconnects, which tells us that the disconnect shall be located in accordance with Section 680-12, Disconnecting Means. (A disconnecting means shall be provided and be accessible, located within sight from all pools, spas, or hot tub equipment, and shall be located at least 5 ft. (1.52 m) horizontally from the inside walls of the pool, spa, or hot tub.)
Section 680-12. Disconnecting Means, refers to pools, spa, or hot tubs, but with this reference to Section 680-12, it now also applies to fountains.
This Section tells us that a disconnecting means shall: be provided (Installed), and be accessible (See Article 100, Definitions, Accessible (as applied to equipment). Admitting close approach; not guarded by locked doors, elevation, or other effective means.) and be located within sight from (See Article 100, Definitions, In Sight From (Within Sight From, Within Sight): Where this Code specifies that one equipment shall be "in sight from,” "within sight from,” or "within sight,” etc., of another equipment, the specified equipment is to be visible and not more than 50 ft (15.24 m) distant from the other.) all pools, spas, or hot tub equipment, and be located at least 5 ft (1.52 m) horizontally from the inside walls of the pool, spa, or hot tub.
(e) Bonding. Shall comply with 600-7.
Subsection (e) informs us that the bonding shall comply with Article 600, Electric Signs and Outline Lighting; Section 600-7, Grounding.
(f) Grounding. Any equipment associated with the sign shall be grounded as per Article 250.
Subsection (f) informs us that any equipment associated with the sign installed in a fountain shall be grounded as per Article 250, Grounding.
Read more by Robert Milatovich
Posted By Craig B. Toepfer,
Monday, March 01, 1999
Updated: Monday, August 27, 2012
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When smog kept suffocating three sprawling cities—Los Angeles, Paris, and Tokyo—in the early 1990s, a standardized infrastructure for charging electric vehicles (Evs) was at last seen as a worthwhile goal. The superiority of clean Evs to dirty gas-powered transportation was borne in on everyone as never before. But Evs stood no chance of success without a refueling infrastructure that matched the corner gas pump for availability and ease of use. The ultimate in convenience would be an infrastructure that let Evs charge up at home.
In France, the government in concert with the national electric utility, Electricite de France, and the domestic auto manufacturers, began an aggressive EV test and development program. In Japan, the Eco-Station demonstration project was established by the Japan Electric Vehicle Association (JEVA). JEVA had been established by the Ministry of International Trade and Industry in 1976 to coordinate EV development among government, universities, research laboratories, and the auto industry. The Eco-Station project offered environmentally friendly vehicles—electric, natural gas, methanol, and others—a familiar gas-station refueling environment. Part of this project resulted in a proposed connector configuration and plans for "fast” charging an EV, that is, charging at least 50 percent of the battery in 15 minutes of less.
Figure 1. The International Electrotechnical Commission (IEC) denotes them by two-letter designations as follows: T-N, T-T, and I-T
In the United States, two events jumpstarted the domestic EV industry—the push in 1990 by the California Air Resources Board for EV mandates to take effect as early as 1998, and the bold declaration by General Motors Corporation, Detroit, at the 1991 North American Auto Show to be the first to market with an EV. In response, the Electric Power Research Institute (EPRI), Palo Alto, California, organized the Infrastructure Working Council (IWC) in 1991 to rally experts from the electric utility, automobile, and electrical equipment industries to address the issues of EV infrastructure for battery charging—charging system architecture, couplers, and technical and societal impacts.
Every major new technology from radio to TV (black and white, color, and high-definition) and VCRs, from computers to Evs relies on basic technical standards to make the transition from invention to commercial success. In the early 1990s, the groundwork for an EV industry was laid by a carefully coordinated international effort to establish a common means of charging EVs and to develop standards to ease their commercialization.
Figure 2. They rely variously on an isolated supply, an isolated charger, or a nonisolated charge
The experts worked in various forums to understand the challenges, set boundary conditions, and negotiate the standards development process. The result has been the timely creation of standards, so that Evs may be produced and sold just as the auto industry is moving from demonstration and development to production.
Starting from Scratch
A standard electrical charging connection is analogous to the familiar gas pump nozzle, but it presented unique challenges to these experts. After all, spilling a few drops of gasoline at the pump is not inherently dangerous to the klutz, but spilling a few coulombs onto the human body is. Unlike duel, which must be vaporized or ignited to create a hazardous condition, electric power flows in an energized state that must be handled carefully.
In fact, connecting an EV to the electrical network for charging presents an unprecedented set of conditions. For the first time in history, consumers, members of the general public of all ages, would be asked to make a high-power electrical connection—typically between 5 and 150kW—perhaps once or twice a day, and outdoors in all types of weather.
Consumer safety was of the essence. Thus, the top priority requirements of a standard EV charging system and associated "”plug”" were that it first and foremost be not only safe, but perceived as safe; that it be intuitive and easy for consumers to use; and that it be cost-effective. Ideally, too, a standard charge coupler between the vehicle and power source would be compatible with electric networks around the world.
Figure 3. The three available methods are cord with a plug end, cored with a connector end, and cord set
This set of conditions mandated a double-fault safety management system to circumvent or mitigate potential shock hazards from the standard EV charging system. In other words, a consumer would still be protected while connecting the vehicle to the power source despite one or even two failures in the safety system.
Classical electrical safety management techniques, which serve as the basis for electrical safety standards around the world, require the systematic layering of basic (insulation), fault (fuse), and additional (ground-fault circuit interrupters) protective measures. The exact measures used vary with the nature of the product involved (in this case, electric-vehicle chargers); its electrical characteristics (voltage, current, frequency, and network configuration), type of user (general public or qualified persons); and conditions of use. The perception of safety is slightly less well defined, but most would grant that seeing exposed conductive elements could discomfit the casual user, and touching them could be even more upsetting.
Standard household and industrial wiring devices prompted the criterion that the plug be easy for consumers to use. However, the electrical connectors under consideration were not. Instead, they were very large and heavy to accommodate the power levels under consideration, required a certain orientation for proper use, and needed significant insertion force. To compound matters, most standardized wiring devices had not been designed for high-durability applications where the connection must be made as often as daily (possibly more frequently) and in all types of weather.
Figure 4. The system architecture basically consists of a high-frequency converter connected to the power supply off-board the vehicle, a high frequency take-apart transformer at the vehicle interface, and an on-board rectifier and charge controller
The cost impact of the EV charging infrastructure on vehicle, electric utility, consumer, and society had to be carefully considered. In the absence of an installation designed for the purpose, the relative costs could only be evaluated by establishing a basic charging system architecture—location of charging apparatus, inlet, and charging control, and the speed and size of the charger. In turn, this would drive the allocation of cost between the vehicle and the supply network and determine the interface or coupler cost.
In an ideal world, a single coupler design would be developed that was compatible with the different electrical characteristics of networks used in every country. Over and above their well-known differences in voltage and frequency, these networks have three basic configurations. The International Electrotechnical Commission (IEC) denotes them by two-letter designations as follows: T-N, T-T, and I-T [Fig.1}.
The first letter, T or I, describes the relationship of the system to earth. T, for terra or earth, indicates that the system is earthed or grounded and this is by far the most widely used network. The I designation indicates that the system is isolated from earth or in some cases connected to earth by a controlled impedance.
The second letter designation identifies the relationship of exposed conductive parts (the prongs on a plug or the slots on the receptacle—for example, to the installation of earth. In this case, T signifies that the utilization equipment is directly earthed independent of the system earth and N, neutre or neutral, signifies that the protective earth of the utilization equipment is connected to or common with the system earthing conductor.
The T-N system is the most popular and can be found in North Central, and South America, many areas in Europe, most of Asia, Australia, and much of Africa. The T-T system is used primarily in France, Southern Europe, and Northern Africa.
In developing an appropriate EV charging infrastructure, a system-level approach had to consider all aspects—the generation, transmission, and distribution of electricity, the wiring systems in homes, commercial buildings, and industrial facilities, the special equipment for charging, and the EV.
A tremendous advantage of EVs is that they are the ultimate alternative fuel vehicles. They shift reliance from a single fuel—gasoline—to the broad range of primary feedstock used for electric power generation—coal, natural gas, oil, nuclear, hydro, and renewables. Subsequently, an improvement is electric-utilityi generation efficiency can be realized by charging EVs during periods of low (off-peak) demand—overnight. This allows increased use of larger more efficient baseload generating facilities.
The exploitation of off-peak capacity establishes the first boundary condition for EV charging—that the charge process take no longer than 8 to 10 hours. Simple mathematics provides nominal charging requirements. Representative values, such as 4 5-8 km/kWh and a desired customer driving range of 160-240 km. yield battery capacities around the 20-50-kWh range and charge rates of 3-9kW, or 6kW nominal, when charger and battery charge efficiencies are factored in.
Figure 5. The conductive ac/dc-coupled system is based on a standard coupler interface and an open system architecture that supports the use of either on-or off-board charges, all of the three possible connection schemes, and voltage, current, and voltage
In North America, where 240-V single-phase is the most common electrical supply, this yields a 30-A circuit, on a par with an electric clothes dryer. That value is well within reach of the transmission, distribution, and installed-service capabilities in use everywhere. This is particularly true when charging overnight, when electricity usage is lowest and most economical, is considered. In a nutshell, the compatibility of EV charging with the existing network neatly sidesteps the costs of upgrading transmission, distribution, and electrical services.
The next step in establishing standards is to set boundary conditions for the EV charging system architecture. A battery charger in essence performs two basic functions: it converts alternating into direct current, and it regulates the voltage in a manner consistent with he ability of a battery to accept current. There are three recognized methods of connecting a battery to the network through a charger. They rely variously on an isolated supply, an isolated charger, or a nonisolated charger [Fig. 2]. All of these methods have unique merits and should be accommodated in a general architecture scheme.
Plugging in, Turning on
A second key consideration in EV charging is the vehicle’s physical connection to the supply network. The three available methods are cord with a plug end, cored with a connector end, and cord set [Fig. 3]. The most popular and familiar methods of connecting equipment is to attach a cord and plug to the appliance and connect to a receptacle or electrical outlet. (Typically, plugs have prongs that fit into a receptacle; connectors do not.)
This works fine with stationary devices that are connected and generally left alone such as a lamp, range, dryer, stereo, TV, and so on. It works less well for EVs where daily or more frequent connection in all weather conditions and safely managing and storing a large cord on the vehicle, especially for high-power fast charging, becomes technically unreasonable and a potential consumer inconvenience.
Because a dedicated circuit with special equipment will probably have to be installed to charge an EV, the auto manufacturers unanimously agreed that the familiar gasoline pump configuration where the hose (cord) and nozzle (plug or connector) are fixed to the pump (charging equipment) is the preferred method. This solution combines convenience with flexibility in coping with special conditions, such as long distances between charging equipment and the vehicle inlet. The third methods of using a cord set fitted with a plug and connector was considered as acceptable for limited situations such as charging from a common existing receptacle.
Given the above scenario where equipment operating at 200V in Japan, 230V in Europe, and 240V in the United States and 40 A nominal, is the preferred and most popular method of EV charging-—known as Level 2 charging—two other methods that address EV customer concerns were also considered. From the start, customers had been worried about the charge time and access to charging facilities. To reassure them, what have come to be known as Level 3 and Level 1 charging were established.
Level 3 or fast charging replenishes more than half of the battery capacity in approximately 10-15 minutes at a commercial public facility. Note that the IWC set the levels and their basic criteria. Level 3 charging is particularly suited to fleet applications where a 15-minute opportunistic charge during a lunch break can significantly extend a vehicle’s daily range and use.
Level 1 charging allows a vehicle to access the most popular grounded standard outlet. Since most garages in the United States have a 120-V/15-A duplex outlet, and similar receptacles abound in other countries, being able to hook up for EV charging is handled by an adapter cord set (a cord with one plug end and one connector end). However, the limited power capability of this outlet and regulations governing circuit sharing and continuous loads (steady demand for 3 hours or more) restrict Level 1 charging to emergency or limited convenience use in North America.
The long-term vision of EV charging includes a mix of facilities. The highest-priority charging points are points of access at home and workplace. Public access charging at such facilities as malls, airports, and park and ride mass transit stations compliments these primary points. Commercial, public fast-charge stations further encourage EV use by solving range limitations and consumer concerns over long charge times.
A standard connector or plug for charging must support the basic charging system architecture. Whatever the charging system configuration and battery type or size, and regardless of customers’ conviction that it is the auto makers’ job to service the battery, the auto makes concurred that control of the charge process would reside on the vehicle—regardless of where the charger is located—to optimize the performance of the battery. Subsequently, two coupler technologies, inductive and conductive, have been the focus of technical and standards development.
The great debate: inductive…
Shortly after announcing its intention to be the first to market with an EV, General Motors indicated it would be using a unique inductive coupler technology for connecting its vehicle to the network for charging. The core element is based on the concept of a take-apart transformer. The system architecture basically consists of a high-frequency converter connected to the power supply off-board the vehicle, a high frequency take-apart transformer at the vehicle interface, and an on-board rectifier and charge controller [Fig.4].
The system is fundamentally an isolated-charge type with the off-board power electronics serving as a current source as commanded by the on-board charge controller. In regulating charge rate, the charge controller communicates with the frequency converter over a close-cooupled radio-frequency media link using a standard J1850 Class B Data Communications Network Interface and the recently developed J2293 protocol for EV charging, both from the Society of Automotive Engineers (SAE).
Increasing the frequency from the line to the 100-kHz-plus range reduces the size of the plug to allow ease of use for the consumer. Functionality and interoperability are ensured by strict control of both the off- and on-board equipment, yielding a system standard as opposed to just a coupler standard.
The inductive system is presently being used with the GM EV1 and Nissan Altra EV. High-power versions, up to 120kW, have been demonstrated. A second generation of the inductive system is currently being jointly developed by GM and Toyota Motor Corporation, Tokyo.
Other auto manufacturers opted to develop a more traditional approach based on simple contact technology. The conductive ac/dc-coupled system is based on a standard coupler interface and an open system architecture that supports the use of either on-or off-board charges, all of the three possible connection schemes, and voltage, current, and voltage/current source chargers [Fig. 5].
For primary Level 2 charging, most OEMs prefer an on-board charger where ac power is supplied to the vehicle over an intelligent switch, and the network protective earth is connected to the vehicle chassis during charging. In these circumstance, the charger design can be optimized for the vehicle and the infrastructure costs can be minimized to include only the contactor, enclosure, and supervisory electronics to ensure safe operation.
For Level 3 fast charging, the size and weight of the charger mandated that it be an off-board device, with dc power being transferred to the vehicle. But the system also accepts lower-rate off-board chargers. In this case, hardwire communication media is used by the vehicle controller to regulate charging using the same SAE J1850 and J2293 standards as the inductive system.
The interface to support an ac/dc conductive coupled system [Fig. 5 again] is a nine-pin configuration for North America consisting of:
- Two single-phase ac contacts rated 240V ac 60 A, and 14.4 kVA.
- Two dc contacts rated 600 V dc, 400A, and 240 kW.
- One equipment ground, sized for fault clearing.
- One control pilot signal contact for the control, interlock, ground monitoring, and ampacity marking functions.
- Three signal contacts for the hardwire communication media.
The mated coupler components, connector, and vehicle inlet can be populated with whatever power and communication contacts are required by the supply equipment or vehicle. The equipment ground and control pilot contacts are always required.
The coupler design uses a butt-type contact and is derived from the product developed for the EV test and demonstration program in France. This design was selected by SAE after extensive durability testing of the basic contacts and the prototype components. With this design, the contacts are shielded on the connector and inlet when disconnected. During the insertion and rotation involved in connection, the shields are automatically retracted. This method of connection and type of contact produced a design that was easy to use, even when configured for high-power dc transfer, and provided an additional safety measure.
Setting the standard
The recommendations of the EPRI-IWC Connector and Connecting Station Committee were published in December 1993, and codes and standards development for charging equipment proceeded apace through the next few years. In the United States, under the auspices of the EPRI-IWC Health and Safety Committee, a panel of experts was convened to develop an article (standard) on EV charging equipment for the 1996 National Electrical Code® (NEC). The proposed revisions were to include Article 625, Electric Vehicle Charging System Equipment. The result was approved for publication in the 1996 NEC and has been updated for the 1999 NEC. Also during this period, the SAE EV Charging Systems Committee developed and approved SAE Recommended Practices for conductive (J1772) and inductive (J1772) charging systems.
Development of a consensus on product standards was initiated by Underwriters Laboratories Inc., in step with activities of the SAE and NEC. Presently, outlines of investigations are under way to establish three EV-related product standards. They are UL 2202, UL 2231, and UL 2251. UL 2202 is the proposed standard for EV charging equipment and covers all nonvehicle electrical equipment for EV charging. UL 2231 is the proposed standard for personnel protection systems for EV supply circuits and covers the requirements for a layered system of double-fault protection for both grounded and isolated charging system. UL 2251 is the proposed product standard for plugs, receptacles, and couplers for EVs.
Incidentally, UL 2231 came out of a comprehensive UL study funded by EPRI, Ford, GM, and Chrysler on personnel protection. Although it presently applies to EV charging systems, it is suitable for general electrical equipment and may be more broadly applied in the future.
With the selection of two charging technologies, conductive and inductive, and their means of coupling, codes and standards are in place or in development in the United States to support EV commercialization. Similar efforts are ongoing in Canada and Japan, and within the IEC.
Canada has revised Part I of its electrical code by adopting Section 86 for EV charging systems and is starting on Part 2, product standards, this year. These standards are or will be closely harmonized with their U.S. equivalents.
The Japan Electric Vehicle Association has published four standards governing conductive EV charging equipment, which from a system architecture standpoint, are closely akin to the U.S. and Canadian standards. An exception is the connecting means, which presently uses the product developed for the Eco-Station project described earlier.
As for the IEC’s Technical Committee 69 for Electric Road Vehicles, its Working Group 4 for charging infrastructure is close to circulating a committee draft for voting. This document has received active input from representatives of the automotive industry around the world and is also harmonized to the extent possible with North American and Japanese activities. If approved, this document will set the requirements for the European community and other IEC member countries.
As the year 2000 approaches, EVs are rapidly moving from demonstration to volume production, thanks in large part to the technical community. In cooperation with standards development bodies, it has delivered a strong foundation for a safe, efficient, and high-value EV charging infrastructure that addresses the complexities of the supply network and vehicle interface with a harmonized solution. Only one question remains: will conductive or inductive charge-couplers prevail in the long-term marketplace?
Copyright © 1998 by November IEEE. Reprinted, with permission fromIEEE Spectrum Magazine, pgs. 41-47. Reprinted with permission.
Read more by Craig B. Toepfer
Posted By NEMA ,
Monday, March 01, 1999
Updated: Monday, August 27, 2012
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The National Electrical Manufacturers Association has just what you need to answer your circuitbreaker application and preventive maintenance questions. NEMA publishes two standards that provide a wealth of information to help users and specifiers select and maintain circuit breakers.
NEMA Standards Publications AB 3-1996 and AB 4-1996 can answer application questions and preventive maintenance questions for molded case circuit breakers. Proper use of these standards can help prevent fire and shock hazards, down-time due to systems failures, and other operations mishaps.
The two NEMA standards serve a different purpose than the standards used to certify circuit breakers. Molded case circuit breaker manufacturers in the US certify their products to the safety and performance requirements defined in the Underwriters Laboratories Inc. UL 489 standard. When circuit breakers meet or exceed these requirements UL permits their listing Mark to be placed on the circuit breaker. Electrical inspectors that enforce electrical codes look for this listing Mark when approving electrical installations.
While knowledge of the construction and performance requirements is important to manufacturers, information regarding the application, field testing, and maintenance of circuit breakers is more important to specifying engineers, installers, and maintenance personnel. That information is found in these two NEMA standards.
If you specify molded case breakers:
The NEMA AB3-1996 standards publication, Molded Case Circuit Breakers and Their Application, describes the types of circuit breakers available and many of their specific applications. It also lists circuit breaker accessories and ratings, and provides guidance on the selection of circuit breakers. Finally it defines much of the terminology associated with circuit breaker products. In addition to molded case circuit breakers, NEMA AB3 covers molded case switches and their accessories.
Section 5 of NEMA AB3 is especially useful for those who select circuit breakers. This section covers the following topics:
- electrical system parameters environmental conditions (extreme temperatures, humidity, corrosive atmospheres)
- feeder and branch circuit breakers
- load considerations
- temperature ratings of conductors and conductor ampacity
Section 5 also includes a detailed explanation on the following:
- time-current curves
- series-combination ratings
- capacitor switching considerations
- motor loads
- ground-fault protection
- circuit breakers used in DC voltage systems
Finally, Section 5 provides a basic overview of the UL standards requirements for the Listing of circuit breakers.
If you inspect or maintain molded case breakers:
The NEMA AB4 standards publication, Guidelines for Inspection and Preventive Maintenance of Molded Case Circuit Breakers used in Commercial and Industrial Applications, provides guidance for maintenance and field testing of circuit breakers and explains how to evaluate the condition of a circuit breaker. NEMA AB4 provides basic procedures that may be used to inspect and maintain molded case circuit breakers rated up to and including 1000 volts, 50/60 Hz ac or ac/dc. The test methods described in NEMA AB4 may be used to verify certain characteristics of circuit breakers originally built and tested to the requirements of the UL 489 and NEMA AB1 standards. However, it is not intended, nor is it adequate, to verify proper electrical performance of a molded case circuit breaker which has been disassembled, modified, rebuilt, refurbished, or handled in any manner not intended or authorized by the original manufacturer.
These test methods are intended for field use only and are non-destructive. They cannot be used to verify all performance capabilities of a molded case circuit breaker, since verification of certain capabilities requires destructive testing.
Some industrial users have indicated that they are required to conduct periodic operational tests of their circuit breakers. The non-destructive tests outlined in Section 5 of NEMA AB4 may be used to verify certain operational characteristics of molded case circuit breakers including:
- mechanical operation
- insulation resistance
- individual-pole resistance
- inverse-time overcurrent tripping
- instantaneous overcurrent tripping
- rated hold-in current
Section 6 describes tests for the proper use of devices such as shunt trip and undervoltage trip releases, electrical operators that allow opening and closing the circuit breaker from a remote location, auxiliary switches that operate when the circuit breaker opens or closes, and alarm switches that operate when the circuit breaker trips automatically.
The NEMA AB3 and NEMA AB4 standards publications are valuable tools for the safe and efficient operation of molded case circuit breakers. They are indispensable to contractors, specifiers, plant engineers, and maintenance personnel. Keep these NEMA standards in mind the next time you have an application or maintenance question concerning molded case circuit breakers. For a copy of AB3 or AB4 call NEMA at 703/841-3201 or IHS at 800/854-7179.
About NEMA: NEMA is the trade association of choice for the electrical manufacturing industry. Founded in 1926 and headquartered near Washington, D.C., its approximately 450 member companies manufacture products used in the generation, transmission and distribution, control, and end-use of electricity.
Posted By Arthur "Bud" Botham,
Monday, March 01, 1999
Updated: Monday, August 27, 2012
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Imagine yourself with the responsibility to provide more than 50,000 amps of safe electrical power over 140 miles of distribution cable powering 5,000 lighting units, day and night, for over seven months.
Now add the following: 3,000 "practical” units will be repeatedly submerged in sea water, and, if that’s not enough, hundreds of swimmers will be in close proximity to these submerged sources while fully energized.
This was the reality set before the production crew as they embarked upon the creation of the most complex motion picture in history—Titanic.
Photo 1. The components that make up the advanced ground-fault current interrupter (GFCI) include a 40-amp single phase, 400-amp GFCI-RCMA service, and the panel mount GFCI. On the left is the panel mount 40/60-amp single or 3-phase, center is the 400-amp
Here is the story about a safety problem as old as harnessed electrical power itself … and about a new solution which was found and successfully executed (without executing anybody).
Back in 1986, camera operator Bill Masten and electrician Rick Prey formed a company, SMS Inc., with the slogan, "The Quiet Mobile Generator Company.” Primarily known for their award-winning NiteSun products—portable generator trucks which boomed 12k HMIs to heights of 120 ft—these two had provided necessary equipment to the production world for over a decade.
When Prey, a Navy trained electrician, worked on The Abyss, they used the electrical equipment that was available at the time, .and it scared us to death,. says Prey. He had worked on several shows involving water, and found that the equipment they needed wasn’t available. They could buy the appliances, but found that .we had protection, but not personnel protection.”
On his next assignment, Crimson Tide, Prey and gaffer Dwight Campbell realized that the equipment was still insufficient. Prey and Masten had been tinkering with ideas, and had come closer with modular devices from the Bender Corporation, when Campbell started working on Hard Rain. But the problem wasn’t solved. .It still wouldn’t pass UL standards. No standards even existed for three-phase GFCIs,” says Masten.
Prey and Masten decided to tinker away at a prototype. With sketches in hand, they went to Bender Engineering with their ideas.
Photo 2. The components that make up the advanced ground-fault current interrupter (GFCI) include a 40-amp single phase, 400-amp GFCI-RCMA service, and the panel mount. (Left to right): 3-phase GFCI for chainmotors; 200-amp GFCI single or 3-phase; 100-amp
PowerGuard is the most advanced single and three-phase Ground Fault Circuit Interrupter (GFCI) personnel protection device in the world and the only three-phase GFCI currently UL listed for personnel protection. Before Titanic it didn’t exist. Here’s how it happened.
For Masten and Prey, "Titanic was a call we had been waiting for. Cinematographer Russ Carpenter, gaffer John Buckley and rigging gaffer Mike Amorelli had less than two weeks to find a 1200-amp GFCI that would work and wouldn’t cause false tripping … nothing was available,” says Masten.
Amorelli emphasizes that, "safety was the most significant aspect of our planning for the picture. The scope of the production alone made this a fact of life. In addition to safety, director Jim Cameron wanted the highest level of reality. That meant literally hundreds of people in, around and under the water, with hundreds of lighting units. Knowing all of this, we made safety the number one concern for all of us.”
"John and Mike had to thread the eye of the needle on Titanic in regard to electrical safety,” explains Carpenter. "Because of the complexity of many of the sets, John’s crews were rigging some stages weeks before the first unit got to them. John and his team had to ascertain how to route power into sets that moved, submerged, or in some cases, literally broke apart. He had to consult with the production designer, mechanical effects supervisor, the director and those persons in charge of water distribution in order to determine what would, in even the wildest scenario, become wet or immersed. Amorelli explains that, "To meet Russ and John’s lighting requirements, we needed a combination of HMIs, incandescents, dimmers and ‘specialized’ lighting units. John and I knew that DC power would not accommodate all of our needs. Traditional methods for handling AC around water were insufficient for a project on the scale of Titanic (50,000 amps were needed for the ship alone). We needed a 1200-amp GFI.”
Photo 3. Captains of their ship: Bill Masten (left) and Rick Prey (right) in front of their NiteSun truck
Masten and Prey figured that with Bender Corporation’s efforts on the Magnetic Levitation Train, "we had a lead,” says Prey. They thought that some of the technology could be applied to their prototype. Marcel Tremblay of Bender agreed to study their schematic. Joe Boardman, then Chris Bender in Germany, and their German lab became involved. Gary Glick at Siemens provided lab time and prototypes.
Buckley recalls that "safety was paramount throughout Titanic. Cameron insisted, and we all agreed, we couldn’t do this film without absolute safety. Approximately 350 people would be in the water. AC power was the only real choice to accomplish the task, and, of course, that had never been done on the scale with which we were dealing. Remember, the greatest amount of lighting equipment ever assembled was also subjected to the elements for over seven months. Right from the beginning, I knew that we needed fault protection devices capable of protecting circuits of twelve hundred amps. Just over two weeks before we started, nothing of that kind existed. We had to have them … period! Some people said, ‘You’re crazy to even try it.’ We turned to SMS because I knew Rick Prey and Bill Masten had built a lot of equipment. Rick listened to our .problem. and agreed to ‘try it.’”
Adds Carpenter, "On the one hand, they had to create a device which avoided serious injury to people in the water and yet wouldn’t be false tripping all the time, costing expensive down time while we waited for the systems to be reset. That dictum translated into serious research, development and testing of the new GFI systems by our team and the folks at SMS.”
Explains Joe Boardman, Bender Engineering, "Rick Prey called and told us about Titanic. We listened to the rather amazing set of problems the film would confront. The magnitude of power needed was beyond the scope of the ‘standards’ for any existing GFCIs and the harsh environment was another factor. We learned that the movie industry in general offers a singular mode of operation. It uses a wide range of voltages which often change. It combines all the facets of a large industrial site, yet it’s a highly mobile endeavor. As one crew member put it … ‘It’s like the circus without the elephants…’”
"After days of calls to countless electrical engineers,” explains Amorelli, "we concluded that while the theory was sound, no one had ever built a GFI of that size.” After we contacted SMS, "Rick and Bill tackled the problem.”
In short order, the prototype arrived in Mexico. Amorelli recalls that "after changes were made, testing was completed and we had the first ever 1200-amp GFI in the business. All totaled, SMS built twenty-eight 1200-amp GFIs, a number of 100-amp 120-volt and 100-amp 240-volt models. The PowerGuards allowed us to safely operate the most complex lighting scheme I’ve ever encountered and on the grandest scale ever attempted.”
Buckley explains that without ever "losing sight of all those cast and crew members we would have in the water when thousands of lights were sunk with the ship, we began to test. This was an anxious period for us. But it worked! I knew we could safely light Titanic in spite of the wet environment. Once, a high wind dragged a piece of heavy duty lighting equipment into the water. The PowerGuard system shut down instantly. We used over twenty of the 1200-amp units on the show. I know that they saved lives.”
Bender Corporation’s Marcel Tremblay explains their involvement. "We felt that here was a unique opportunity to work together with SMS on solutions. However, there was a limited time frame. With a sketch of the electrical distribution layout from Rick and a lot of cooperative effort between us, we developed a prototype. But it had to comply with existing and developing standards. If its sensitivity were too great, it would be tripping all the time. The goal was to have a device that could sense minute currents at the ‘let-go’ level and that would incorporate features such as an inverse time curve to prevent false tripping when used in circuits rated as high as 400 amperes. This meant literally expanding the technology envelope. The standards didn’t even mention three-phase power for personnel protection.”
The founders of SMS were just 80% "there” when the call came from Titanic. Masten explains, "Mike told us we would have 50,000 amps in water with people, in two weeks. We said, ‘We’ll try.’ The race was on for a working prototype. We had amazing help from Bender, Siemens and the Titanic crew to close the gap.”
Pressure? The prototype took eighteen months. As Titanic shoved off, PowerGuard was, at last, a reality.
Not long after the field test results were in, Bender Corporation’s staff worked out some changes until they had a unit that would provide the highest level of "people protection” ever. The system worked. Recently it has received the UL listing for personnel protection.
Adds Tremblay, "We look to the future now with the knowledge that this breakthrough will improve safety throughout the industry. New products already at hand allow the crew to check the condition of the entire electrical setup even before it is even energized.”
Necessity is most often credited for new inventions. It is ironic that RMS Titanic was credited with bring many life-saving inventions to sea travel and the world, following her tragic end. Luckily, nobody had to die on a film shoot in order to necessitate the invention of the PowerGuard.
It has been said, "Most things we will use in our daily lives, just ten years from now, have not yet been invented.” The film Titanic gave birth to a life-saving device, the PowerGuard.
Amorelli notes, "Technical breakthroughs made on this film will give directors new avenues to achieve the heightened sense of reality and greater production values demanded by today’s sophisticated audiences. I am proud to have been a part of a project where technological advances, such as the development of the 1200-amp GFI, were conceived and realized.”
What’s next for Rick Prey and Bill Masten? Currently, they are refining the equipment, and have also branched out into insulation detection for leaking equipment. This insulation detection device was recently used in the Bellagio Hotel in Las Vegas. As for the GFCI, having generated such success on Titanic, it has moved on to other features. Its list of credits reads like a seasoned veteran: Godzilla, Sphere, The Negotiator, Virus, Mafia, and EDtv.
As the Bender Engineering team said, "We are proud that PowerGuard gave those who made this wonderful film (Titanic) a safer workplace.”
For Bill Masten and Rick Prey, they agree that "Titanic has made history and made all of us who were part of its creation a part of that history … who can ask for more than that?”
Read more by Arthur "Bud" Botham
Posted By J. Philip Simmons ,
Sunday, November 01, 1998
Updated: Monday, August 27, 2012
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Bonding (Bonded):"The permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.” N
Bonding jumper, Main:"The connection between the grounded circuit conductor and the equipment grounding conductor at the service.”N
Main bonding jumper
The main bonding jumper is one of the most critical elements in the safety grounding system. This conductor is the link between the grounded service conductor, the equipment grounding conductor and in some cases, the grounding electrode conductor. The primary purpose of the main bonding jumper is to carry the ground-fault current from the service enclosure as well as from the equipment grounding system that is returning to the source. In addition, where the grounding electrode conductor is connected directly to the grounded service conductor bus, the main bonding jumper ensures that the equipment grounding bus is at the same potential as the earth.
Figure 5-1. Main bonding jumper
For a grounded system, Section 250-28 requires that an unspliced main bonding jumper be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor of the electrical system. The connection is required to be made within the enclosure for each service disconnect.
An example of this is where two or more service disconnecting means in individual enclosures are grouped at one location. This type of installation often is made with a wireway or a short section of busway installed downstream from the metering equipment. In other cases, a wireway or short section of busway is installed ahead of metering and is supplied by a service lateral or service-entrance conductors. Sets of service-entrance conductors supply each of the service disconnecting means. Service disconnecting means are installed from the wireway or auxiliary gutter. (If there are nipples between the disconnecting means and the metal or nonmetallic trough, the trough meets the definition of a wireway from Article 362 rather than an auxiliary gutter from Article 374.) Section 250-28 requires a main bonding jumper be installed in each service disconnect enclosure. As previously mentioned, Section 250-24(b) requires that the grounded service conductor be brought to each service disconnecting means and be bonded to the enclosure. The main bonding jumper is the means to accomplish this requirement.
Figure 5-2. Main bonding jumper—multiple enclosures
The rules are a little different where more than one service disconnecting means is in a common enclosure. This equipment usually consists of listed switchboards, panelboards or motor control centers.. Where more than one service disconnecting means is located in an assembly listed for use as service equipment, Section 250-28 Exception No. 1 permits the grounded service conductors to be run to a single grounded conductor bus in the enclosure and then be bonded to the assembly enclosure. This means that only one main bonding jumper connection is required to be installed from the common grounded conductor bus to the assembly enclosure. The sections of the assembly are bonded together by means of an equipment grounding conductor bus or by being bolted together.
Exception No. 2 to Section 250-28(b) permits alternate means for bonding of high-impedance grounded neutral systems. See Chapter Four of the IAEI Soares Book on Grounding for methods and requirements for grounding high-impedance grounded neutral systems. Also see NEC® Sections 250-36 and 250-186 for the specific requirements and allowances.
The main bonding jumper is permitted to consist of a wire, bus, screw or other suitable conductor. It must be fabricated of copper or other corrosion-resistant material. Aluminum alloys are permitted where the environment is acceptable. In addition, where the main bonding jumper consists of a screw, it must have a green finish that is visible with the screw installed. This green finish assists in identifying the bonding-jumper screw from the other screws that are on or near the neutral bus. See Sections 250-28(a) and (b).
Figure 5-3. Main bonding jumper for listed assembly
Functions of Main Bonding Jumper
The main bonding jumper performs three major functions:
- Connecting the grounded service conductor to the equipment grounding bus or conductor and the service enclosure.
- Providing the low-impedance path for the return of ground-fault currents to the grounded service conductor. The main bonding jumper completes the ground-fault return circuit from the equipment through the service to the source as is illustrated in Figure 5-4.
- Connecting the grounded service conductor to the grounding electrode conductor. Under certain conditions given in Section 250-24(a)(4), it is permitted to connect the grounding electrode conductor to the equipment grounding terminal bar rather than to the terminal bar for the grounded service conductor. This scheme is common on larger switchboard services and is necessary for proper operation of certain types of equipment ground fault protection systems. See Chapter 15 of the IAEI Soares Book on Grounding for additional information on this subject.
Size of main bonding jumper in listed enclosures
Where listed service equipment consisting of a switchboard, panelboard or motor control center is installed, the main bonding jumper that is provided with the equipment is rated for the size of conductors that would normally be used for the service. The method for sizing of the main bonding jumper in listed service equipment is found in Underwriters Laboratories Safety Standard for the equipment under consideration and is verified by the listing agency. Therefore, if a main bonding jumper that is a bus bar, strap, conductor, or screw is furnished by the manufacturer as part of the listed equipment, it may be used without calculating its adequacy. Section 384-3(c) requires the equipment manufacturer to provide the main bonding jumper.
Figure 4. The main bonding jumper completes the ground-fault return circuit from the equipment through the service to the source
Size of main bonding jumper at single service-disconnect or enclosure
Since the main bonding jumper must carry the full ground-fault current of the system back to the grounded service conductor (which may be a neutral), its size must relate to the rating of the service conductors which supply the service. The minimum size of the main bonding jumper is found in Table 250-66 as required by Section 250-28(d). This relationship is based on the conductor’s ability to carry the expected amount of fault current for the period of time needed for the overcurrent device to open and stop the flow of current.
For example, where 250 kcmil aluminum service-entrance conductors are installed, the main bonding jumper is found to be No. 4 copper or No. 2 aluminum by reference to Table 250-66.
The size of the main bonding jumper does not directly relate to the rating of the service overcurrent device. Do not attempt to use Table 250-122 for this purpose. Table 250-122 gives the minimum size of equipment grounding conductors for feeders and circuits on the load side of the service.
Sizing of main bonding jumper for parallel service conductors
Figure 5-5. Main bonding jumper at single disconnect
Where service conductors are installed in parallel, (connected together at each end to form a larger conductor) the total circular mil area of the conductors connected in parallel for one phase are added together to determine the minimum size main bonding jumper required. See Section 250-28(d). For example, where three 250 kcmil conductors are connected in parallel per phase, they are treated as a single 750 kcmil conductor. By reference to Table 250-66 the main bonding jumper, if aluminum service-entrance conductors are used, is 1/0 copper or 3/0 aluminum.
Where the service-entrance conductors are larger than the maximum given in Table 250-66, Section 250-28(d) requires the main bonding jumper to be not less than 12½ percent (0.125) of the area of the largest phase conductors.
This is illustrated by the following example:
Three 500 kcmil copper conductors are installed in parallel as service-entrance conductors.
3 x 500 kcmil = 1500 kcmil.
1500 x .125 = 187,500 circular mils.
Since a 187,500 circular mil conductor is not a standard size, we next refer to Chapter 9, Table 8 to find the area of conductors.
The next conductor exceeding 187,500 circular mils is a No. 4/0 AWG conductor which has an area of 211,600 circular mils. It is always necessary to go to the next larger size conductor since the 12½ percent size is the minimum size permitted.
Follow a similar procedure for determining the minimum size main bonding jumper required for other sizes of parallel service-entrance conductors.
Figure 5-6. Main bonding jumper for parallel runs
Bonding of service conductor enclosures
Special rules are provided for bonding enclosures on the line side of the service disconnecting means. This is due to the fact that this equipment does not have overcurrent protection on its line side such as feeders and branch circuits have. Fault current of sufficient magnitude must flow during a short period of time to allow the fuse on the line side of the utility transformer to open. The level of fault current and particularly the duration the current may flow could be much larger than would flow in a feeder or branch circuit as there is not an overcurrent device in series with the conductor.
The basic rule is that all metallic enclosures that contain a service conductor must be bonded together. The bonding ensures that none of the equipment enclosures can become isolated electrically and become a shock hazard should a line-to-ground fault occur. The bonding also provides a low impedance path for fault current to flow in so the fuse or circuit breaker on the line side of the electric utility transformer will open.
Sizing of equipment bonding jumper on line (supply) side of service.
Equipment bonding jumpers on the line side of the service and main bonding jumper must be sized to comply with Table 250-66. This is required by Section 250-102(c). For example, where 250 kcmil copper conductors are installed as service-entrance conductors, Table 250-66 requires a No. 2 copper or 1/0 aluminum bonding jumper.
Where the sum of the circular mil area of the service-entrance phase conductors exceeds 1100 kcmil copper or 1750 kcmil aluminum, the equipment bonding conductor must be not less than 12½ percent (0.125) of the area of the ungrounded phase conductors.
Figure 5-7. Size of equipment bonding jumper on line side of service
Sizing of equipment bonding jumper for parallel conductors
Two methods are provided for bonding service raceways that are installed in parallel. The first method is to add the circular mill area of the service-entrance conductors per phase together and treat them as a single conductor. The bonding jumper size is determined from Table 250-66 and is connected to each conduit bonding bushing in a "daisy-chain fashion.” This method often results in an equipment bonding jumper that is quite large and difficult to work with.
For example, if five 250 kcmil copper conductors are installed in parallel for a phase, the equipment bonding jumper for bonding the metal raceways must not be smaller than 3/0 copper.
This is determined as follows:
Five x 250 kcmil = 1250 kcmil.
1250 kcmil x .125 = 156,250 circular mils.
Figure 5-8. Size of equipment bonding jumper on line side of service
The next larger conductor found in Chapter 9, Table 8 is 3/0 with an area of 167,800 circular mils.
In this case, a 3/0 copper equipment bonding conductor must be connected from the grounded service conductor or equipment grounding bus to each metal raceway in series (daisy-chain fashion from one raceway to another).
A more practical method of performing the bonding for services supplied by multiple raceways may be to connect an individual bonding conductor between each raceway and the grounded service conductor terminal bar or equipment grounding bus. This is permitted by Section 250-102(c). This will usually result in a smaller equipment bonding conductor which is easier to install.
Again, using the example above and referring to Table 250-66, the minimum size equipment bonding conductor for the individual raceways containing 250 kcmil copper service-entrance conductors is No. 2 copper or 1/0 aluminum. A properly sized equipment bonding jumper is installed from the terminal bar for the grounded service conductor or from the equipment grounding terminal bar to each conduit individually.
Different conductor material
Section 250-28(d) provides instructions on sizing the main bonding jumper or equipment bonding jumper on the supply side of the service where different conductor materials are used for the service-entrance conductors and the bonding jumper. The procedure involves assuming the phase conductors are of the same material (copper or aluminum) as the bonding jumper and that they have an equivalent ampacity to the conductors that are installed. This is illustrated as follows:
Assume aluminum phase conductors and a copper bonding jumper are installed.
Three 750 kcmil Type THW aluminum conductors are installed.
From Table 310-16, 385 amperes x 3 = 1155 amperes. The smallest type THW copper conductor that has an equivalent rating is 600 kcmil with an ampacity of 420.
Next, determine the total circular mil area of the copper conductors.
Three x 600 kcmil = 1800 kcmil.
1800 kcmil x .125 = 225 kcmil.
The next standard size is 250 kcmil copper which is the minimum size bonding jumper permitted to bond equipment at or ahead of the service equipment in this example.
Bonding service equipment enclosures
The Code requires that electrical continuity of service equipment and enclosures that contain service conductors be established and maintained by bonding. The items required to be bonded together are stated as follows in Section 250-92(a):
(1) The service raceways, cable-trays, cablebus framework or service cable armor or sheath.
(2) All service equipment enclosures containing service conductors, including meter fittings, boxes or the like, interposed in the service raceway or armor.
(3) Any metallic raceway or armor which encloses the grounding electrode conductor. (This subject is covered in detail in Chapter 7 of this text.)
An exception to this requirement for bonding at service equipment is mentioned in Section 250-92(a)(1). It refers to Section 250-84 which has rules on underground service cables that are metallically connected to the underground service conduit. The Code points out that if a service cable contains a metal armor, and if the service cable also contains an uninsulated grounded service conductor which is in continuous electrical contact with its metallic armor, then the metal covering of the cable is considered to be adequately grounded.
Figure 5-9. Bonding service equipment enclosures
Use of neutral for bonding on line side of service
Section 250-94(1) permits the use of the grounded service conductor (may be the neutral) for grounding and bonding equipment on the line side of the service disconnecting means. This is also permitted by Section 250-142(a)(1). (Two other applications of this bonding are explored in later chapters of the IAEI Soares Book on Grounding.) Often, connecting the grounded service conductor to equipment such as meter bases, current transformer enclosures, wireways and auxiliary gutters is the most practical method of bonding these enclosures.
Usually, self-contained meter sockets and meter-main combination equipment are produced with the grounded conductor terminals or bus (often a neutral) bonded directly to the enclosure. The enclosure is then effectively bonded by the connection of the grounded circuit conductor to these terminals. No additional bonding conductor connection to the meter enclosure is required. Current from a ground fault to the meter or meter-main enclosure will return to the source by the grounded service conductor (may be a neutral) and, hopefully, will allow enough current to flow in the circuit to operate the overcurrent protection on the line side of the utility or other transformer.
Figure 5-10. Use of neutral for bonding on line side of service
In addition, meter enclosures installed on the load side of the service disconnecting means are permitted to be grounded (bonded) to the grounded service conductor provided that:
(a) Service ground-fault protection is not installed; and
(b) The meter enclosures are located near the service disconnecting means. (No distance is used to clarify what is meant by the word "near.”), and
(c) The size of the grounded circuit conductor is not smaller than the size specified in Table 250-122 for equipment grounding conductors. See Section 250-142(b) Exception No. 2.
Means of bonding at service equipment
The methods for bonding at service equipment are outlined in Section 250-94. These requirements for bonding are more restrictive at services than downstream from the service. The reason this is so important is service equipment and enclosures may be called upon to carry heavy fault currents in the event of a line-to-ground fault. The service conductors in these enclosures have only short-circuit protection provided by the overcurrent device on the line side of the utility transformer. Only overload protection is provided at the load end of the service conductor by the overcurrent device. This is one of the reasons the Code limits the length of service conductors inside of a building.
Figure 5-11. Methods of bonding service equipment
Bonding of these enclosures is to be done by one or more of the following methods from Section 250-94:
(1) Bonding to the grounded service conductor through the use of exothermic welding, listed pressure connectors such as lugs, listed clamps, or other listed means. These connections cannot depend solely upon solder.
(2) Threaded couplings and threaded bosses in a rigid or intermediate metal conduit system where the joints are made up wrench-tight. Threaded bosses include hubs that are either formed as a part of the enclosure or are supplied as an accessory and installed according to the manufacturer’s instructions.
(3) Threadless couplings and connectors are permitted where they are made up tight for rigid and intermediate metal conduit and electrical metallic tubing and metal-clad cables.
(4) Other approved devices such as bonding-type locknuts and bushings.
Bonding jumpers are required to be used around concentric or eccentric knockouts that are punched or otherwise formed so as to impair an adequate electrical path for ground-fault current. It is important to recognize that concentric and eccentric knockouts in enclosures such as panelboards, wireways and auxiliary gutters have not been investigated for their ability to carry fault current. Where any of these knockout rings remain at the conduit connection to the enclosure, they must always be bonded around to ensure an adequate fault-current path.
Figure 5-12. Bonding fittings
The Code states here that "Standard locknuts or bushings shall not be the sole means for the bonding required by this section.” This statement does not intend to prevent the use of "standard” locknuts and bushings, it is just that they cannot be relied upon as the sole means for the bonding that is required by this section. "Standard” locknuts are commonly used outside the enclosure on conduit that is bonded with a bonding bushing or bonding locknut inside the enclosure. Standard locknuts are used to make a good, reliable mechanical connection as required by Section 300-10.
Parallel bonding conductors
Section 250-102(c) requires that where service-entrance conductors are paralleled in two or more raceways or cables and the equipment bonding jumper is routed with the raceways or cables, the equipment bonding jumper must be run in parallel.
In this case again, the size of the bonding jumper for each raceway is based upon the size of the service-entrance conductor in the raceway by referring to Table 250-66.
Grounding and bonding of remote metering
Figure 5-13. Parallel bonding conductors
As mentioned before, Section 250-92(a) requires all equipment containing service conductors to be bonded together and to the grounded service conductor. This includes remote (from the service equipment) meter cabinets and meter sockets.
Grounding and bonding of equipment such as meters, current transformer cabinets and raceways to the grounded service conductor at locations on the line side of and remote from the service disconnecting means increases safety.
This equipment should never be grounded only to a grounding electrode such as a ground rod. Figures 5-14 and 5-15 show why. If a ground-fault occurred at this line-side equipment, and it is not bonded as required, the only means for clearing a ground fault would be through the grounding electrodes and earth. Given the relatively high impedance and low current-carrying capacity of this path through the earth and high resistance of grounding electrodes such as rods, little current will flow in this path. This leaves the equipment enclosure(s) at a dangerous voltage above ground potential just waiting to shock or possibly electrocute a person or animal that may contact it. The voltage drop across this portion of the circuit can easily be calculated by using Ohms Law. (Resistance times the current gives the voltage.) There are many records of livestock being electrocuted while contacting electrical equipment that was improperly grounded. Sections 250-2 and 250-54 require that the earth not be used as the sole equipment grounding conductor or fault-current path.
The most practical method for grounding and bonding this line-side equipment is to bond the grounded service conductor to it. As can also be seen in Figures 5-14 and 5-15, a ground fault to the equipment will have a low impedance path back to the source through the grounded service conductor. This will allow a large current to flow in the circuit to cause the overcurrent protection on the line side of the transformer to clear the fault.
Supplementary grounding electrodes
In accordance with Section 250-54, it is permissible to install a grounding electrode at the remote meter location shown in Figures 5-14 and 5-15 to supplement the grounded service conductor. This Code section refers specifically to grounding electrodes supplementing the equipment grounding conductors. Some electric utilities require a grounding electrode at meter equipment installed remote from service equipment such as on poles. The Code in Section 230-66 makes it clear that individual meter socket enclosures are not to be considered service equipment. The same is true for metering equipment installed in remote current-transformer enclosures. As mentioned earlier, it is critically important that these meter enclosures be properly bonded as they contain service conductors.
This additional grounding electrode will attempt to keep the equipment at the earth potential that exists at the meter location. In addition, the electrodes at the remote meter and at the service location are bonded together by the grounded service conductor installed between the metering and service equipment. This brings the installation into compliance with Section 250-58 which requires a common grounding electrode or where two or more electrodes are installed, they must be bonded together.
As previously stated, these grounding electrodes should never be used as the only means for grounding or bonding these enclosures or to carry fault current.
More extensive discussion of this subject is found in Chapter Six of the IAEI Soares Book on Grounding.
Bonding of multiple service disconnecting means
Installation of multiple services as permitted by Section 230-2(a) through (d) and installations of services that have multiple disconnecting means can take several forms. Additional services are permitted by Section 230-2 for:
(a) Fire pumps, emergency, legally required, standby, optional standby or parallel power production systems.
(b) By special permission, for multiple occupancy buildings where there is no available space for service equipment that is accessible to all occupants, or, for a single building or structure that is large enough to make two or more services necessary.
(c) Capacity requirements; where the service capacity requirements exceed 2,000 amperes at 600 volts or less, where load requirements of a single-phase installation is greater than the serving utility normally provides through a single service, or by special permission (related to capacity requirements).
(d) Different characteristics of the services such as different voltages, frequencies, or phases, or for different uses, such as for different rate schedules.
The basic rule for sizing of the equipment bonding jumper for bonding these various configurations is found in Section 250-102(c). This section requires that the bonding jumpers on the line side of each service the main bonding jumper be sized from Table 250-66. Also, the size of the bonding jumper for each raceway is based on the size of service-entrance conductors in each raceway. As discussed earlier, conductors larger than given in Table 250-66 are required for larger services. Since different sizes of service-entrance conductors may be installed at various locations, the minimum size of the equipment bonding conductor and main bonding jumper is based on the size of the service-entrance conductors at each location.
For example, the appropriate size of bonding jumper for the installation in Figure 5-16 with the assumed size of conductors is as follows: (all sizes copper)
|Service-Entrance Conductor||Bonding Jumper|
|a. 500 kcmil in service mast||1/0|
|b. 1000 kcmil in wireway||2/0|
|c. 300 kcmil to 300 ampere service||No. 2|
|d. 3/0 to 200 ampere service||No. 4|
|e. No. 2 to 125 ampere service||No. 8|
A practical method for bonding the current transformer enclosure and wireway (sometimes referred to as a "hot gutter”) is to connect the grounded service conductor directly to the current transformer enclosure or wireway. This may be done by bolting a multi-barrel lug directly to the wireway and connecting the neutral or grounded service conductors to the lug. Be sure to remove any nonconductive paint or other coating that might insulate the connector from the enclosure.
As previously discussed, the grounded service conductor must also be extended to each service disconnecting means and be bonded to the enclosure.
Excerpted from Chapter 5 of the IAEISoares Book on Grounding, 7th Edition
Read more by J. Philip Simmons
Posted By J. Philip Simmons,
Tuesday, September 01, 1998
Updated: Friday, August 24, 2012
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We published a photograph in the "Code Violations” section of the March/April 1995 IAEI News which shows 21 service disconnecting means that are grouped in the same location on the end of an apartment building. Four service laterals supply the building from a common transformer. The caption with the photograph indicates that the installation is in violation of Section 230-71(a) of the National Electrical Code® as there are more than six disconnects grouped at the same location.
After getting a few phone calls asking for clarification of the Code requirements as well as three letters indicating disagreement with our conclusion, we published a Closer Look article on services for multiple-occupancy buildings in our July/August 1995 IAEI News. The article was based on the rules in the 1993 NEC®.
We decided to take another look at these requirements since several changes have taken place in Code rules since that time. Some key definitions of terms used in Article 230 have changed as well. Where used in this article from this point on, terms that are defined in Article 100 are in italics. That is just to help remind us that these terms have precise meanings as used in the NEC®. As is true with many discussions of subjects related to any code, it is important to have a good understanding of definitions that apply to the installation under consideration. These terms have a specific meaning where used in the Code.
We will take a brief tour through some of the basic requirements in the Code that apply to the installation as well as review the applicable definitions. This discussion is based on the 1999 National Electrical Code®.
Section 230-2 has had a change of format as well as been rewritten to change the previous exceptions into positive language. There is now a general rule that requires, "A building or other structure served shall be supplied by only one service unless permitted in (a) through (d).” These subsections contain six of the former seven exceptions to the general rule. Language identical or similar to this has been in many editions of the Code. For the purpose of our discussion, we will assume that the multifamily dwelling under consideration does not have a fire wall that would qualify as a building separation as mentioned in Article 100. In addition, we will not cover Section 230-2(a) Special Conditions (applies to installations of services for fire pumps, emergency systems, etc.) or Section 230-2(d) Different Characteristics, as multifamily dwellings are generally supplied at one voltage level and system type.
As an aid to the reader, we have underlined new words added to the definitions since the 1996 NEC® and struck through words that are deleted. The definition of "service” has been revised in the 1999 NEC® and is now defined in Article 100 as, "The conductors and equipment for delivering electric energy from the serving utility electricity supply system to the wiring system of the premises served.” These changes clarify that on-site power production such as solar photovoltaic systems, generators and power production facilities such as cogeneration systems are usually separately derived systems and not services. The term "service” is a broad term that includes the service drop, service lateral, service-entrance conductors (both overhead and underground system) and service equipment which includes the service disconnecting means. Of course, the definition of "equipment” is also a very broad general term that includes "material, fittings, devices, appliances, fixtures, apparatus, and the like used as a part of, or in connection with, an electrical installation.”
The term "service equipment” has also been revised in the 1999 NEC® and is now defined in Article 100 as, "The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s), and their accessories, connected to the load end of service located near the point of entrance of supply conductors to a building or other structure, or an otherwise designated defined area, and intended to constitute the main control and means of cutoff of the supply.” As can be seen, the term "service equipment” includes the equipment, such as switches and fuses as well as circuit breakers, that are used as the "service disconnecting means.”
The term "service disconnecting means” is not defined in the NEC®, although the term is used in several articles including the definition of "service conductors” in Article 100. Section 230-70 contains several requirements for the service disconnecting means and also describes its purpose. The service disconnecting means is or are provided to "disconnect all conductors in a building or other structure from the service-entrance conductors.” It must be located "at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors.” Each service disconnecting means must be permanently marked to identify it as a service disconnecting means and must be suitable for the prevailing conditions, such as being suitable for a wet location.
The term "building” is defined in Article 100 as, "A structure that stands alone or that is cut off from adjoining structures by fire walls with all openings therein protected by approved fire doors.” The term "structure” is not defined in the Code although Section 230-21 mentions "such as a pole” when describing an "other structure.” Since the term is not defined in the Code, we can use a common dictionary definition such as "Something made up of a number of parts held or put together in a specific way.” So, we can apply the rules for installation of service equipment to any building or structure the service equipment is mounted in or on.
The term "service conductors” has also been revised in the 1999 NEC® and now is defined in Article 100 as "The supply conductors that extend from the service point street main or from transformers to the wiring system service equipment of the premises supplied.” The term "service conductors” is a broad term that includes: "service drop,” "service-entrance conductors, overhead system,” "service-entrance conductors, underground system” and "service lateral.” This change coordinates with Section 90-2(b)(5) which indicates that installations under the exclusive control of electric utilities for distribution of electric energy are not covered by the Code. However, these same conductors installed by the owner, contractor or electrician are covered by the Code.
As can be seen, the conductors supplied by an electric utility on the line side of the "service point” are now not considered by the Code to be "service conductors.” The term "service point” is defined in Article 100 as, "The point of connection between the facilities of the serving utility and the premises wiring.” This means that where the service point is at the building or structure such as the connection at the weatherhead for overhead services or at the meter socket for underground services, the service drop and service lateral are not covered by the Code.
The following definitions also apply to our discussion and should be understood:
"Service Drop: The overhead service conductors from the last pole or other aerial support to and including the splices, if any, connecting to the service-entrance conductors at the building or other structure.”
"Service-Entrance Conductors, Overhead System: The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop.”
"Service-Entrance Conductors, Underground System: The service conductors between the terminals of the service equipment and the point of connection to the service lateral.
(FPN): Where service equipment is located outside the building walls, there may be no service-entrance conductors, or they may be entirely outside the building.”
"Service Lateral: The underground service conductors between the street main, including any risers at a pole or other structure or from transformers, and the first point of connection to the service-entrance conductors in a terminal box or meter or other enclosure with adequate space, inside or outside the building wall. Where there is no terminal box, meter, or other enclosure with adequate space, the point of connection shall be considered to be the point of entrance of the service conductors into the building.”
With these definitions in mind, let’s look at the requirements in Section 230-2 for installing a service for a multiple-occupancy building. The general rule in this section is that "A building or other structure shall be supplied by only one service unless permitted in (a) through (d).” Keep in mind that the term "service” includes, "The conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served.”
Figure 1. An overhead service to a building and an underground service to another.
The general requirement is that only one service drop or service lateral is permitted to be run to a building or other structure where the service equipment is located. Why? Because the term "service” includes both the "service drop” and "service lateral” and Section 230-2 generally permits only one service to a building or structure. The service drop will connect to service-entrance conductors, usually "outside the building, clear of building walls.” (See the definition in Article 100.) As can be seen in the definition of "service lateral,” where the service lateral stays outside the building such as supplying weatherproof service equipment, there are no service-entrance conductors.
Structure with a Fire Wall
A structure with a fire wall that qualifies as a building separation is considered to be more than one building as determined by the number of fire-wall separations. For example, a structure with one fire wall will be two buildings. The fire resistance rating of a fire wall required to qualify as a building separation is not given in the NEC®. It is necessary to obtain the details on fire-wall construction to create a building separation from the applicable building code. Usually, a fire wall having not less that a two-hour rating is required to create a building separation. Each of these buildings is then generally permitted to have not more than one service to it. Have you seen a duplex (two-family dwelling) with two service drops or service laterals to it? This is a violation of Section 230-2 unless the structure has a qualifying fire wall.
A permanent plaque or directory is required where more than one service is permitted for any reason, be it fire-wall separation or one of the conditions of Section 230-2(a) through (d). This requirement applies where a building or structure is supplied by any combination of more than one service, feeder or branch circuit. The plaque or directory must be located at each service disconnect location and must indicate all other services, feeders or branch circuits supplying that building or structure and give the area served by each of them. See Section 230-2(e).
Section 230-2(b) Special Occupancies
(This previously was Section 230-2 Exception No. 3, Multiple-Occupancy Buildings.) This subsection permits additional services, by special permission, for (1) Multiple-occupancy buildings where there is no space for service equipment accessible to all occupants, and for (2) A single building or other structure sufficiently large to make two or more services necessary.
The term "multiple-occupancy building” is not defined in the NEC® but "multifamily dwelling” is. Traditionally, the term multifamily dwelling has been interpreted as a multiple-occupancy building in applying the rules of the NEC®. Building codes tend to use the term "occupancy” as referring to a class of users of a building such as "business use,” "educational use” or "residential use.” So, a multiple-occupancy building in building code terms would have more than one type of occupancy in the same building and might be referred to as a "mixed use or occupancy” building. The NEC® tends to use the phrase "multiple-occupancy building” as one having more than one occupant rather than more than one class of occupant.
Note that Section 230-2(b)(1) permits an additional service(s) where there is "no available space for service equipment,” that is "accessible to all the occupants.” It seems there will always be space available for a single main disconnecting means, or up to six disconnecting means grouped at one location that is be accessible to all the occupants. This service equipment does not have to be inside such as in an electrical equipment room but can be located outside on or adjacent to the building. The location rule is in Section 230-70(a) and reads, "The service disconnecting means shall be installed at readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors.” Economical design criteria may dictate not installing a single main service disconnecting means but that consideration is not given in this Code rule. In addition, there may not be space at one location for all the metering equipment and individual meter/mains needed for a large complex. However, this section does not address multi-metering or feeder disconnecting means for all the individual occupancies. The installation in the photograph at the beginning of this article fails the test for this subsection as there certainly appears to be space at the location chosen for the multiple services for a single service to be installed with meter/feeder supply to the individual dwelling units.
There is no requirement in this rule that the space available for the service equipment that is to be accessible to all the occupants must be inside the building. It is quite common to locate service equipment outside multiple-occupancy buildings as indicated in the photograph that accompanies this article. If there is space for the service equipment in a common area, including outside, that is adequate for the service equipment for the building, Section 230-2(b)(1) cannot be used. If space is available for the service equipment to serve all the occupancies, then, according to the main rule, only one service is permitted for the building with a maximum of six disconnects. (We will look at some other provisions a little later in this article.)
Where the main disconnecting means is or are located before the metering equipment, it is common for the serving utility to require that the service disconnecting means enclosure be locked to reduce the likelihood of tampering and theft of electrical energy. The authorization for more than one service in Section 230-2(b) must be by "special permission,” which is defined in Article 100 as "The written consent of the authority having jurisdiction.”
It is not necessary for there to be a fire wall separation to grant the "special permission” provided for in this subsection. As provided in Section 230-2(b), "special permission” is to be based on space-for-equipment considerations. Six service disconnecting means are permitted to be installed for each additional service that is allowed by the authority having jurisdiction under Section 230-2(b)(1). The Code does not clearly require that the additional services installed as permitted by this subsection be installed at a location separate from the other service(s) to the building. For example, a building is supplied by a 120/240 volt, single-phase service with six service disconnecting means grouped at one location. A second service, this one a 208Y/120 volt, three-phase service, can be installed immediately adjacent to the single-phase service with an additional six service disconnecting means. See Section 230-71(a).
(This previously was Section 230-2 Exception No. 5, Buildings of Large Area.) Again, by special permission, one or more additional services are permitted for "A single building or other structure sufficiently large to make two or more services necessary.”
No guidance on how to determine what qualifies as a "building of large area” is provided in the NEC®. Large industrial plants where lengthy feeder runs would cause excessive voltage drop which would require increasing the conductor size unreasonably is an example of where this exception may be applied. Other examples are large shopping centers or high-rise office buildings. The authority having jurisdiction is pretty much left on his own when attempting to determine when to allow this subsection to be applied.
Obviously, this subsection does not apply to the installation under review as there are no long feeder runs involved.
Section 230-2(c). Capacity Requirements
(This subsection is the former Exception No. 4 to Section 230-2.) This subsection permits additional services to a building or other structure for only the following reasons, all of which are related to the capacity or size of the service:
"(1). Where the capacity requirements are in excess of 2000 amperes at a supply voltage of 600 volts or less; or
(2). Where the load requirements of a single-phase installation are greater than the serving agency normally supplies through one service; or
(3). By special permission.”
Condition "(1)” does not apply to this installation as there is no service in excess of 2000 amperes. The total ampacity of the four service laterals do not come close to 2000 amperes. In fact, the size of the four service laterals could no doubt be smaller if they were combined to serve all the loads. This is due to the increased demand factors permitted by Article 220 for load calculations as the number of units served increases.
One disadvantage of installing the service lateral conductors in parallel (connected together at both ends to form a larger conductor) is the fault current available at the service equipment will be greater than where individual sets of conductors are run to separate service equipment enclosures.
Condition "(2)” does not apply as the four service laterals shown in the photograph are from the same transformer and thus obviously do not exceed the capacity of the serving utility’s transformer.
Condition "(3)” provides for special permission from the authority having jurisdiction. To apply in this situation, the special permission must relate to the capacity of the system. Condition "(3)” does not seem to apply to the installation under review as there is no need for an additional service based on capacity considerations. The single transformer installed by the utility has adequate capacity for the load.
Sections 230-2 and 230-40 Exception No. 2
Former Exception No. 7 to Section 230-2 has been incorporated into the opening paragraph of Section 230-2 as a new second sentence. The sentence reads, "For the purpose of Section 230-40, Exception No. 2 only, underground sets of conductors, size 1/0 and larger, running to the same location and connected together at their supply end but not connected together at their load end shall be considered to be supplying one service.” This sentence really does not allow an additional service in the strictest sense but allows several sets of service lateral conductors to be considered as supplying one service. (In reality, the service lateral does not supply the service but is a part of the service as defined in Article 100.)
As indicated, the second sentence of Section 230-2 is limited in application to Section 230-40 Exception No. 2. It reads, "Where two to six service disconnecting means in separate enclosures are grouped at one location and supply separate loads from one service drop or lateral, one set of service-entrance conductors shall be permitted to supply each or several such service equipment enclosures.”
As illustrated in Figure 4, a maximum of six service laterals, sized 1/0 or larger, that are connected together at their line end, but not at their load end, are considered to be supplying one service. The service laterals must be run to a common location at the building or structure served and are permitted to supply one, two or up to a total of six service disconnecting means. However, no more than six disconnecting means are permitted to be grouped at the location being served by these service laterals. See Section 230-71(a).
Section 230-40 Exception No. 1
Section 230-40 generally permits a service drop or service lateral to supply not more than one set of service-entrance conductors. When taken with the requirements of Section 230-2 and the definition of "service” in Article 100, this means that a building or other structure can generally be supplied by only one service drop that connects to one set of service-entrance conductors or it can be supplied by one service lateral that connects to one set of service-entrance conductors.
Exception No. 1 to Section 230-40 provides that, "Buildings with one or more than one occupancy shall be permitted to have one set of service-entrance conductors for each class of service run to each occupancy or group of occupancies.”
Figure 5 illustrates an underground supply to a multiple-occupancy building. A similar procedure can be followed for an overhead supply. While only six units are shown due to space limitations, any number of units may be served in a similar manner.
The service lateral supplies a metering cabinet that does not contain service disconnecting means or overcurrent protection but has only meter sockets. A set of service-entrance conductors is run to each occupancy or to a group of occupancies. Of course, these service-entrance conductors do not have overload protection until they terminate in the service equipment. Where this scheme is selected, it is customary to run service-entrance conductors to the individual units rather than to a group of units. Up to six disconnecting means are permitted in or on each of the units, and of course, they must be grouped at the individual locations to comply with Section 230-71 (a).
Figure 6. Service lateral conductors are run from the utility transformer to a wireway mounted below the meter sockets.
As indicated in the Figure 6, service lateral conductors are run from the utility transformer to a wireway mounted below the meter sockets. Service-entrance conductors are spliced to the service lateral conductors within the wireway and run through the meter sockets to each unit. Service disconnecting means and overload protection is provided in or on each unit.
The location of the service disconnecting means must comply with Section 230-70 (a) which requires, "The service disconnecting means shall be installed at a readily accessible location, either outside of a building or structure or inside nearest the point of entrance of the service conductors.” Some inspection jurisdictions interpret, "nearest the point of entrance of the service conductors” to require the service equipment to be located in the stud space in the outside wall or back-to-back with the meter socket or point of entrance. Others interpret this rule to permit up to four feet of service-entrance conductors inside the building, while still others permit as much as 25 feet of service-entrance conductors to be installed inside the building. In some cases where these longer lengths of service-entrance conductors are permitted inside the building by local rule, a limited number of wiring methods are permitted. Be certain to verify the local rule or interpretation before beginning an installation.
This section provides that, "The service disconnecting means for each service permitted by Section 230-2, or for each set of service-entrance conductors permitted by Section 230-40, Exception Nos. 1 or 3, shall consist of not more than six switches or six circuit breakers mounted in a single enclosure, in a group of separate enclosures, or in or on a switchboard. There shall be no more than six disconnects per service grouped in any one location.” Since the term "location” is not defined in the Code, it will be applied based on its common dictionary meaning. As this word applies to the installation in the first photograph, most people probably would apply the meaning of "location” to be that all the service disconnects shown are at the same "location” since they are immediately adjacent to each other at the same end of the building. Most people would likely consider the services to be in different "locations” if a service were installed some significant distance apart such as at opposite ends of the building.
As we previously mentioned, more than six service disconnects are permitted at the same location only where more than one service is permitted to a building. For the installation under consideration, it does not appear that any of the rules in Section 230-2(a) through (d) apply so only one service with a maximum of six disconnecting means is permitted.
This section generally requires the service disconnecting means permitted by Section 230-71 to be grouped.
In a multiple-occupancy building, each occupant is required to have access to their service disconnecting means. The exception to Section 230-72(c) allows the service disconnecting means that supplies more than one occupancy to be accessible to authorized building management personnel only where the electric service and electrical maintenance for the building are under continuous building management supervision. This exception does not apply to the multiple-occupancy installation under consideration as all the service disconnecting means are on the outside at a common location and are accessible to each of the occupants.
As can be seen, there are many different ways to install the service for a multiple-occupancy building and be in compliance with the National Electrical Code. To do so requires a thorough reading and understanding of the definitions and Code requirements that apply. As you have probably observed, the installation shown in the photograph at the beginning of this article did not comply with the 1993 or 1996 NEC and would not comply with the revised rules of the 1999 NEC Article 230.
Serving utilities may have local requirements regarding serving multiple-occupancy buildings that must be complied with. These utilities often have booklets with diagrams that illustrate their distribution requirements.
Finally, the authority having jurisdiction may have local amendments to the Code that must also be complied with as well. These amendments will be in the form of legally adopted ordinances, regulations or statutes and are not simply an unwritten interpretation. These local amendments, if any, are also available in writing from the inspection agency.
Read more by J. Philip Simmons