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 Leslie Stoch ,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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Usually we can assume that the rules of the Canadian Electrical Code are based on some basic principles, which don’t vary a whole lot — to minimize the possibilities of electrical fire and shocks. But are the rules ever in direct conflict with each other or their principles?
Thankfully, we don’t need to consider this question too often. Rules are generally written to be consistent with other rules and some firmly held electrical safety principles. However, Rule 14-l00(d) in the 1998 Canadian Electrical Code seems to have strayed some distance from the fold. Here is the new 1998 code rule:
"Each ungrounded conductor shall be protected by an overcurrent device at the pointwhere it receives its supplyof current and at each pointwhere the size of the conductor isdecreased,except that such protection shall be permitted to be omitted: (d) Where the conductor:
(i) Forms part of the only circuit sup- plied from a power or distribution transformer rated over 750 kV with primary protection in accordance with Rules 26-252(1), (2), and (3) and that supplies only that circuit; and
(ii) Terminates in a single overcurrent device with a rating not exceeding the ampacity of the conductor(s) in the circuit; and
(iii) Is protected from mechanical damage
The basic electrical safety principle provided in the code is pretty clear — we have to provide overcurrent protection for conductors at points of supply or where conductor size is reduced. Rule 14-100 gives us a few exceptions under some very controlled conditions. The reasoning — to ensure that unprotected conductors in buildings don’t create any undue electrical fire or shock hazards. This new sub-rule of Rule 14-100 seems to imply that these principles are now changed when the transformer primary voltage exceeds 750 volts.
What Rule 14-100(d) says — we can now run the secondary conductors from a power or distribution transformer as far as we like without overcurrent protection if the transformer primary voltage exceeds 750 volts. The conductor run must still be protected from damage and terminate in a single circuit-breaker or set of fuses which protect conductors at their current ratings.
It seems odd that sources of power should receive different treatment when they are larger (power and distribution transformers with primary voltages above 750 volts). Thisseems even less reasonable when we consider that Table 50 (for primary voltages above 750 volts) allows primary overcurrent protection up to 600%. This of course allows the same multiple of transformer secondary current at the transformer secondary. Add to that the fact that larger power and distribution transformers can deliver higher phase-to-phase and phase-to-ground fault currents, which are not easily detected or interrupted by the transformer primary side protection.
Other 1998 CEC rules appear to support the general principle that conductors must always be protected by properly sized overcurrent and/or ground fault protection, with some closely controlled exceptions. Some examples:
1) Rule 14-102 was originally written to provide ground fault protection, to prevent damage due to low level arcing ground faults in large services and feeders. Obviously, the effectiveness of ground fault protection is greatly reduced when conductors are allowed to travel a long distance through a building before reaching the point where they are protected.
2) Rule 6-206(e) specifies that that the main service box must be "as close as practicable to the point where the consumer’s service conductors enter the building.” Once again, this rule is designed to limit the length of wiring in a building and thereby limit the possibilities for unprotected arcing faults.
3) For the same reasons, Rule 14-100(b) only allows us to reduce wire sizes when conductor runs are restricted to maximum of 3 m and when installed in a totally enclosed raceway, armoured cable or metal-sheathed cable.
4) The same for Rule 14-100(c), which allows us to reduce wire size down to 1/3, but only up to 7.5m with mechanical protection.
5) Rule 14-100(f), a variation of Rule 14-100(c) allows us to reduce primary conductors to a transformer down to 1/3 as long as both the primary and secondary conductors are protected against damage and their total lengths limited to maximum 7.5 m.
If we can assume that all of these rules are designed to minimize the occurrences of arcing faults for unprotected conductors in buildings, why is Rule 14-100(d) so out of tune with the rest? I would be pleased to find out your answers to this puzzling question.
As in previous articles, you should consult the inspection authority in the province or territory as applicable for a more precise interpretation of any of the above.
Read more by Leslie Stoch
Posted By Underwriters Laboratories ,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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Does a UL Listed electric sign require further inspection in the field?
Large signs do. Electric signs so large that shipment in one carton or fully assembled is impractical may be divided into sections. Each major subassembly bears an "Electric Sign Section” Listing Mark. Sign faces, trim and mounting hardware are not considered major subassemblies. Each sign has suitable installation instructions describing or illustrating the proper assembly, mounting and connection of sign sections. The acceptability of the assembled sections in the field, interconnections between sections and the connections to a branch circuit rests with the local authority having jurisdiction.
About Underwriters Laboratories: Underwriters Laboratories® (UL) is an independent product safety certification organization that has been testing products and writing Standards for Safety for over a century. UL evaluates more than 19,000 types of products, components, materials and systems annually with 20 billion UL Marks appearing on 66,000 manufacturers products each year. UL's worldwide family of companies and network of service providers includes 68 laboratory, testing and certification facilities serving customers in 102 countries. UL is also the only National Certification Body (NCB) for PV in North America and an OSHA-accredited Nationally Recognized Testing Laboratory (NRTL). For more information, visit www.UL.com/newsroom.
UL Question Corner
Posted By Underwriters Laboratories,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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How does UL assess water-damaged electrical equipment?
Flooding and other natural disasters prompt many questions about water-damaged electrical equipment. Can the equipment be dried out? Are the circuit breakers and fuses safe to use? Can switchboards be re-energized?
Since flooding usually comes swiftly and unexpectedly, there isn’t always time to shut off electrical equipment. Shut-off switches and electrical control boxes, commonly installed in lower levels of buildings, are often submerged. Besides causing a big mess, water-logged equipment isn’t the only problem facing building owners after a flood. Silt, debris, oil, dissolved chemical substances and other water-borne contaminants can also damage electrical equipment. And, after flood waters recede, rapid mold growth occurs, chemically attacking electrical components.
When approached to investigate flood-damaged electrical equipment, UL investigates equipment on a case-by-case basis. UL considers many factors when providing a review to assess whether to replace or refurbish damaged equipment. These factors include the age of the equipment, the extent of water damage, and corrosion or sediment deposits found in the components.
While the ultimate decision to replace or refurbish equipment is left up to the local code authority and building owner, they can ask UL to visit the flood site to evaluate the equipment that may have been affected, and discuss what can be done to repair, refurbish or replace water-damaged electrical equipment.
After refurbishment and repairs have been made, the owner may ask UL to return to the site to re-evaluate refurbished equipment. Upon completion of this evaluation, UL issues a letter report identifying areas of non-compliance with UL requirements. A copy of this report is also provided to the code or regulatory officials for use in determining the equipment’s suitability for reconnection to the electrical supply. Results of any tests conducted on the refurbished equipment are also provided, if available.
The owner may also request UL to conduct a Field Evaluation or Field Investigation on new replacement equipment that is not UL Listed. A Field Evaluated Product Mark is affixed to equipment found in compliance with UL requirements. Only Field Evaluations result in issuance of a Field Evaluation Product Mark. At the conclusion of a Field Investigation, UL issues a letter report and provides a label to the local acceptance authority for application to the product. It may not always be physically or economically practical to repair or refurbish all equipment damaged during a flood. Consequently, code authorities or UL representatives may advise the building owner to replace damaged electrical equipment with new equipment.
Some cases also require UL to continue inspecting refurbished and repaired equipment over specified time periods to check for any residual degradation caused by flood exposure, or other contaminants not found during the initial inspection. Information gathered from these additional visits are included in separate letter reports and provided to the local code authorities.
UL cannot evaluate flood-damaged equipment for Listing, Classification or Recognition.
For more information about UL’s evaluations of flood-damaged electrical equipment, contact the following Field Evaluation coordinators at the UL office nearest you:
Midwestern United States
Bill Bartunek at (847) 272-8800, ext. 42564
Fax: (847) 509-6219
E-mail address: email@example.com
Eastern United States
Jimmy Wong at (516) 271-6200, ext. 22552
Fax: (516) 439-6045
E-mail address: firstname.lastname@example.org
Southern United States
Bob Eberhardt at (919) 549-1641
Fax: (919) 547-6021
E-mail address: email@example.com
Western United States
Mike Shulman at (408) 985-2400, ext. 32770
Fax: (408) 556-6062
E-mail address: firstname.lastname@example.org
Northwestern United States
Dom Kumandan at (360) 817-5604
Fax: (360) 817-6024
E-mail address: email@example.com
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UL Question Corner
Posted By Philip Cox ,
Saturday, May 01, 1999
Updated: Tuesday, August 28, 2012
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Known as the "keystone of the electrical industry,” the IAEI is a unique organization in which all members of the electrical industry can come together and participate as a group and deal with issues that affect both the industry and the general public. The success of the IAEI is due in part to inspector members going the extra mile and giving much of their own time to better the organization. They have worked hard to provide valuable education and to promote the adoption and enforcement of good electrical safety rules. Unfortunately, some people evidently are under the erroneous impression that because of the IAEI’s name, only electrical inspectors can be members. Not only can those who are not electrical inspectors be members of the organization, but they also can be very active and productive in achieving the goals of the IAEI.
Associate members of the IAEI have always been vital in the growth of the organization. While associate members are not eligible to hold all offices nor to vote on all matters of the IAEI, they in fact exercise most privileges enjoyed by inspector members. For reasons similar to those held by most professional and trade organizations representing a specialized area of skill or expertise, the IAEI must reflect the inspector’s view on such things as organizational positions on electrical code rules. Organizations representing other professions, trades, or crafts generally are effective in representing their members’ special views on electrical code rules and other matters. Each professional or trade organization representing its members’ perspective on matters helps provide valuable technical information and achieves a reasonable balance on such things as the formation and adoption of good electrical safety rules.
Associate members of the IAEI are also vital to its success. That may seem strange to some because associate members are usually part of other organizations dedicated to their own specialized interest. However, some of the strongest advocates of the basic principles upon which the IAEI stands are associate members. Chapters in certain areas have so few inspectors that it must depend on associate members to keep it strong and productive. Associate members are frequently involved in providing or arranging for educational programs that directly benefit IAEI members in general. Many associate members serve as secretary/treasurers of sections, section districts, chapters, and divisions. As covered in an earlier editorial, the role of secretary/treasurer is probably the most demanding and vital for the smooth operation of the IAEI. This in no way degrades the office of president. IAEI presidents are leaders and chief executive officers of their particular section, section district, chapter, and division However, their jobs are much easier where the secretary/treasurer has held the position for an extended time and can provide the president with support and guidance where necessary.
Some of the most productive sections, chapters, and divisions have reached that level because of hard work by associate members. In some locations, associate members have been primarily responsible for seeing that inspector meetings are planned and run well, for locating sources of needed training and arranging for it to be presented , and for numerous other activities that both stimulate interest and address code related needs of members. Associate members who avidly support the IAEI recognize that it is in their best interest for the IAEI to maintain its unbiased position in the industry. They know that if their work with the IAEI focuses only on their own special interest, the independent and unbiased position that is traditionally associated with the IAEI may very well be compromised and that would be detrimental for all its members. Associate members generally understand the importance of a strong IAEI and the support of qualified electrical inspectors. Inspector members also understand the importance of non-inspector members of the IAEI for several reasons and have a great appreciation for the significant work they do for the organization. Achieving the objectives of the IAEI is a joint effort. The IAEI truly is a "keystone of the electrical industry.”
Read more by Philip Cox