Posted By Keith Lofland,
Monday, September 16, 2013
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Whenever I travel across our great country, I never cease to be amazed that the receptacles in my hotel room, in the meeting rooms, in the airports or wherever I go are always the same shape and size. The ungrounded, grounded and equipment grounding slots or "smiley face” are always in the exact position, and the dimensions never change. The power cord for my laptop computer plugs right in every time with no problem. This has to be sheer coincidence, right? No, this is no coincidence at all. All these receptacles are built to a product standard (UL 498) that will ensure our electrical products will be compatible, regardless of our location around the country. As long as the electricity is available when we plug into a receptacle, we tend to take these devices for granted. It’s difficult to improve on these reliable devices, but in this article we consider a few changes in the upcoming 2014 National Electrical Code.
Article 100 of the NECdefines a receptacle as "a contact device installed at the outlet for the connection of an attachment plug.” Article 406 of the NEC is titled, "Receptacles, Cord Connectors, and Attachment Plugs (Caps).” Let’s look at some of the changes in Article 406 and other places that affected our little "smiley face” friends we call receptacles.
406.3(E) and Figure 406.3(E)
Controlled Receptacle Marking
A new subdivision titled "Controlled Receptacle Marking” was added to 406.3, Receptacle Rating and Type. This new subsection will now require a new marking symbol for all nonlocking-type, 125-volt, 15- and 20-ampere receptacle outlets controlled by an automatic control device or by an automatic energy management system. A new symbol was also added in new Figure 406.3(E). An exception follows this rule to indicate that this marking is not required for receptacle outlets controlled by a wall switch to provide the required room lighting outlet(s) as permitted by 210.70(A)(1) Ex. No. 1.
New energy management codes are currently being widely adopted. One such energy management code is ASHRAE 90.1 Energy Standard for Buildings except Low-Rise Residential Buildings. This code requires that up to 50 percent of all 125-volt, 15- and 20-ampere receptacles be automatically controlled. The control could be an energy management system, timer or sensor. The occupant or end user needs to know which receptacle outlets will be automatically controlled and which receptacles will be energized continually. This will avoid loads such as a refrigerator appliance being plugged into the receptacle and then being unintentionally turned off for a time. Automated systems typically control identified loads such as lighting or HVAC equipment with the consequences known and understood. The uncertainty of what is plugged into a controlled receptacle outlet can raise concerns regarding safety as well as convenience; thus, it is essential to be able to identify, readily, receptacle outlets that will be powered on and off automatically.
Figure 1. Receptacles controlled by an automatic control means must be so marked.
406.4(D) Readily Accessible Location for Replacement Receptacles
This new requirement for replacement of receptacles was initiated to align the readily accessible requirements for GFCI devices stated at 210.8 with the rules for GFCI and AFCI protective devices required at 406.4(D). The readily accessible requirement for GFCI receptacles governed at 210.8 was added to the 2011 NEC. Justification for the readily accessible rule at 210.8 was primarily related to occupant or user accessibility to the monthly testing and to the features of the reset device. Just like GFCI protection, AFCI protection can also be accomplished by circuit breaker types or outlet-type devices which have the same monthly testing and reset features. Ready accessibility to these protective devices for replacement receptacles should not be different from that for GFCI devices covered at 210.8.
Figure 2. Exception for tamper-resistant receptacles
was expanded for the 2014 NEC.
406.5(E) Receptacles in Countertops and Similar Work Surfaces
Receptacles are prohibited from being installed ina face-up position in countertops, or similar work surfaces; this prohibition applied only to dwelling units prior to the 2014 NEC. The words "in Dwelling Units” were removed from the title of 406.5(E) to make it clear that receptacles cannot be installed ina face-up position, in countertops or in similar work surfaces, of any type occupancy, not just in dwelling units. If there is a concern about receptacles installed in the face-up position at dwelling units countertops or similar work surfaces for such things as liquid spillage, these same concerns exist at countertops or similar work surfaces of non-dwelling units, as well. Section 406.5(E) also now recognizes "listed receptacle assemblies” for countertop applications. ANSI/UL 498-2012 Standard for Safety for Attachment Plugs and Receptacles in Sections 143, 144 and 146, and ANSI/UL 943-2012 Standard for Safety for Ground-Fault Circuit-Interrupters in Sections 6.28 – 6.29 specifically evaluate and list receptacle assemblies and GFCI receptacle assemblies for countertop applications.
Figure 3. Receptacle outlet is required for each car space.
406.5(F) Receptacles in Seating Areas and Other Similar Surfaces
Receptacles are presently not permitted, according to 406.5(E), to be installed in a face-up position in countertops, or similar work surfaces. In recent times, benches and seating areas in public locations such as airports are being installed with receptacles installed in and on the seating areas. These are typically installed so that someone can sit on these benches and use the supplied 125-volt receptacle outlet for a laptop computer or to charge a cell phone or other electronic hand-held device. In some cases, these receptacles are installed in the face-up position. This represents a hazard in waiting as it is possible in some cases to sit right on the receptacle itself. Spillage — of water, soft drinks, etc. — is another issue involving these "face-up” receptacles. Where there is a need to install such receptacles in benches or other similar surfaces, it should be done with an assembly listed for the application to prevent damage and potential exposure to energized conductors or circuit parts. For the 2014 NEC, strict language was adopted at 406.5(F) that will require receptacles in seating areas or similar surfaces not to be installed in the face-up position unless the receptacle is part of an assembly listed as a furniture power distribution unit (if cord-and-plug-connected) listed to UL Product Standard 962A; or is part of an assembly as household or commercial furnishings listed to UL Product Standard 962. These seating-mounted receptacles can also be listed as a receptacle assembly or as a GFCI receptacle assembly for countertop applications or installed in a listed floor box.
Figure 4. Isolated ground receptacles are not permitted in a patient care vicinity.
406.9(B)(1) 15- and 20-Ampere Receptacles in Wet Locations
Revisions to 406.9(B)(1) have leveled the playing field for dwelling units and non-dwelling unit wet locations as far as "extra duty” enclosures and covers are concerned. The "in-use” covers for wet location, 15- and 20-ampere, 125- and 250-volt receptacles must all be of the extra duty type regardless of its occupancy type location. The requirements for these more rigidly-constructed extra duty covers or hoods at in-use covers for receptacles installed in wet locations was instituted in the 2011 NEC, but at that time, the extra duty cover provision only applied to "other than one- or two-family dwellings.” The durability of the nonmetallic in-use cover hoods provided for compliance with these wet location requirements has been found to be less than desirable, especially on construction sites. Breakage and hinge failure to these nonmetallic hood covers has been reported at dwelling units and non-dwelling units as well, leaving the receptacles exposed to all weather conditions. The more rigorous performance requirements in UL Product Standard 514D, Standard for Cover Plates for Flush-Mounted Wiring Devices, for of these extra duty in-use outlet box hood covers has improved the general durability of all listed in-use covers.
Another revision calls for these extra duty covers at all wet location 15- and 20-ampere, 125- and 250-volt receptacles, not just the ones that are supported from grade. If the receptacle is installed in a wet location, it should make no difference how the enclosure or device box is installed or supported when determining the need for an extra duty hood cover.
Figure 5. The minimum number of required receptacles was increased at health care facilities.
406.12 Exception for Tamper-Resistant Receptacles
The exception for tamper-resistant receptacles (with four specific locations or areas) that applied only to dwelling units in the 2011 NEC, now applies to dwelling units, guest rooms and guest suites of hotels and motels, and to child care facilities. Tamper-resistant receptacles for dwelling units were introduced in the 2008 NEC in an effort to prevent small children from inserting foreign objects (paper clips, keys, etc.) into energized electrical receptacles. An exception (with four areas) was added to the requirement for tamper-resistant receptacles in the 2011 NEC. Tamper-resistant receptacles requirements for guest rooms and guest suites of hotels and motels and for child care facilities were added to the 2011 NEC, as well. These three sections for tamper-resistant receptacles were combined into one section with three subsections, with the exception that applied to dwelling units being moved to apply to all three occupancies for the 2014 NEC. The exception with the four specified locations that was added to the 2011 NEC for dwelling units was warranted, but these exceptions are also needed for guest rooms and guest suites of hotels and motels and for child care facilities. These exempted locations — whether in a dwelling, hotel room, or a child care facility — are out of reach of small children and should be exempted for tamper-resistant receptacle provisions.
406.15 Dimmer Controlled Receptacles
A new section was added at 406.15 to permit specific receptacles to be controlled by a dimmer under specific conditions. A receptacle supplying lighting loads can be connected to a dimmer if the plug/receptacle combination is a "nonstandard configuration” type and is specifically listed and identified for each such unique combination. The electrical industry is starting to see 120-volt cord- and plug-connected lighting, such as rope lighting, being installed under shelving or under cabinets. To power this lighting, conventional 120-volt receptacle outlets are being employed. The concerns begin when the occupant complains that the lighting is too bright, and he wants to control this cord- and plug-connected lighting with a dimmer. Some of the manufacturers of these lighting sources provide a dimming feature that is listed with their product. Clear and concise Codelanguage was needed to ensure that standard grade receptacles cannot be controlled from any dimming or voltage dropping device. This new provision will require a receptacle supplying lighting loads from a dimmer only if the plug/receptacle combination is a nonstandard configuration type and is specifically listed and identified for each such unique combination.
Photo 1. New provisions were added that prohibit receptacles, unless they are part of an assembly listed for the application, from being installed in a face-up position in seating areas or similar surfaces.
Other noteworthy changes in the 2014 NECinvolving receptacles include the following.
210.52(G) Dwelling Unit Garage Receptacle Outlets
A receptacle is now required for each car space in a garage. The garages encountered today at most dwelling units have gone from a simple place to park vehicles out of the elements in a bygone era to "do-it-all” locations where homeowners service their vehicles and/or convert a portion of the garage space to serve as a workshop. In previous editions of the Code, one convenience receptacle outlet was required in this garage location regardless of the size of the garage or the intended use of same. In many instances, this one required receptacle outlet may very well be located behind a large appliance such as a freezer or refrigerator. It is not uncommon in these situations for the homeowner to resort to running an extension cord from this receptacle outlet behind the appliance or from the garage door receptacle outlet, stapling the cord to the ceiling and down the wall to have an additional outlet for convenience use for such things as hand drills, car vacuum cleaners, etc. The majority of dwelling units built today is constructed with two- or three-car garages. This new provision which will now require an additional receptacle outlet for each car space will reduce the use of extension cords currently being used to extend the branch circuit wiring and will provide a safer environment for the homeowner.
Photo 2. "Extra duty” covers are now required for all 15- and 20-ampere, 125- and 250-volt receptacles installed in a wet location (not just for those supported from grade), including dwelling unit wet location receptacles, as well.
210.64 Receptacle at Electrical Service Areas
At least one 125-volt, single-phase, 15- or 20-ampere receptacle outlet is now required to be installed within 15 m (50 ft) of all electrical service areas. There is also an exception added for this rule to exempt one- and two-family dwelling services from this requirement. This new rule is similar to the requirement for a service receptacle outlet to be installed within 7.5 m (25 ft) of all heating, air-conditioning, and refrigeration equipment at 210.63. At the service equipment, there is sometimes a need for connecting portable electrical data acquisition equipment for the qualitative analysis of the electrical system. Test equipment is frequently needed for monitoring and servicing electrical equipment in service areas, as well.
517.16 Use of Isolated Ground Receptacles
The requirement to prohibit isolated ground receptacles in health care facilities was condensed to prohibit these receptacles to a patient care vicinity only of a health care facility. The previous language at 517.16 would prohibit the use of isolated ground receptacles in the entire health care facility. Section 517.16 is located in Part II of Article 517 and, as such, applies to the entire health care facility. The 2012 edition of NFPA 99 Health Care Facilities Code affirms the use of isolated ground receptacles in health care facilities while continuing to forbid their use only within patient care vicinities [see NFPA 99 22.214.171.124.7.1(A) and 126.96.36.199.7.1(B)]. Listed cord- and plug-connected medical instrumentation used in health care facilities outside of patient care vicinities (typically at nurses’ monitoring stations) often requires connection to isolated ground receptacles to insure measurement accuracy by mitigating electrical noise or interference, which is essential to patient medical safety. Allowing isolated ground receptacles away from a patient care vicinity would allow this mitigation against equipment interference without affecting patient safety.
Article 517 Receptacles at Health Care Facilities
The minimum number of receptacles required for general care area patient bed locations of a health care facility was increased from four to eight receptacles at 517.18(B). The minimum number of receptacles required for critical care area patient bed locations of a health care facility was increased from six to fourteen receptacles at 517.19(B). The minimum number of receptacles required for an operating room of a health care facility is now required to be a minimum thirty-six receptacles at 517.30(B). This was an effort to align the NECwith NFPA 99 Health Care Facilities Code. The 2012 edition of NFPA 99 underwent some major modifications, one of which eliminated all occupancy chapters within the document and adopted a risk-based approach as far as the patient is concerned. A new process detailing building systems categories in healthcare facilities was introduced. Category 1 covers facility systems in which failure of such equipment or system is likely to cause serious injury or death of patients or caregivers. Category 2 is facility systems in which failure of such equipment is likely to cause minor injury to patients or caregivers. Category 3 is facility systems in which failure of such equipment is not likely to cause injury to patients or caregivers but can cause patient discomfort. Category 4 is facility systems in which failure of such equipment would have no impact on patient care. These categories are determined by documenting a defined risk-assessment procedure found in NFPA 99.
680.22(A)(1) Required Receptacle(s) at Swimming Pools
At least one 125-volt, 15- or 20-ampere receptacle on a general-purpose branch circuit must be located not less than 1.83 m (6 ft) from, and not more than 6.0 m (20 ft) from, the inside wall of all permanently installed pools. This requirement was expanded to all permanently installed pools, not just dwelling unit permanently installed pools. The title was revised from, "Dwelling Unit(s)” to "Required Receptacle, Location.” For permanently installed pools, at least one 125-volt, 15- or 20-ampere receptacle must be installed in the vicinity of the pool. This receptacle must be GFCI-protected, on a general purpose branch circuit, and must be located not closer than 1.83 m (6 ft) and not farther than 6.0 m (20 ft) from the inside wall of the pool. This receptacle shall be located not more than 2.0 m (6½ ft) above the same floor, platform or grade on which the pool is installed. Prior to the 2014 NEC, this required receptacle was only required at permanently installed pools at dwelling units. This receptacle outlet(s) that service the pool area is commonly used for ordinary devices such as radios, electric grills, bug zappers, etc. This receptacle’s primary function is to limit the use of extension cords around and near the pool’s water edge.
Read more by L. Keith Lofland
Posted By Randy Hunter,
Monday, September 16, 2013
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In the last issue we ended with the requirements for underground installations in 300.5. We’ll pick up where we left off with 300.6, Protection against Corrosion and Deterioration. The basic requirement is that equipment must be suitable for the environment in which it is installed.
Take a look at this section in your code book and you will find a long list of items to be considered related to damage caused by the environment in which electrical equipment is installed. The first item in the list is Ferrous Metal Equipment, which is metal containing an appreciable amount of iron. Since it is sometimes difficult to tell what metal was used just by looking, you can test the metal with a magnet. If the magnet is attracted to the metal, it is a ferrous metal. The NEC states that these materials shall be suitably protected by a coating of an approved corrosion-resistant material; this is commonly achieved by galvanizing during the manufacture of the product. The code also states that for field threaded conduit, you must take the required steps to maintain the corrosion protection while keeping the conductive properties of the conduit. Please review 300.6(A), where you will find additional information regarding different types of protection in (1) through (3). Please also be familiar with your local conditions. Here in southern Nevada, we have very corrosive soil that attacks raceways installed underground, so we’ve had to address some of these conditions with local amendments.
In 300.6(B) through (D) the protection of Aluminum Metal Equipment, Nonmetallic Equipment and Indoor Wet Locations are addressed. A couple of comments are appropriate here regarding nonmetallic systems; if they are exposed to sunlight they need to be listed for such exposure, and if exposed to chemicals they need to be resistant to the hazard. Regarding corrosive locations, there are two common types that come to mind. The first would be a wet battery service location where they are repairing and charging batteries; here you have a heavy concentration of acidic fumes which can quickly destroy metallic raceways. The second is in pool equipment rooms where the equipment is exposed to the fumes of both acid and chlorine concentrations. In both of these locations, I’ve found the preferred method is the use of nonmetallic materials as they will generally outlast metallic equipment. Metallic equipment at times will not last more than a year in such environments, depending on the concentration of the exposure. Lastly, we cover indoor wet locations, which has a simple rule that the entire wiring system (where installed exposed) shall be spaced a ¼″ off the surface. This allows an air space behind the equipment to allow drainage and to prevent a buildup of materials which may cause damage to the equipment.
Photo 1. Art 300.18(B) clearly states that raceways shall not be welded unless designed to be welded, here we have an installation that has welded joints as can be seen by the insets.
Raceways Exposed to Different Temperatures are covered in 300.7; this is a simple requirement, yet often missed in the inspection process. One of the most common occurrences where this applies is where we have wiring methods being installed into the interior of a freezer or cold storage location. The difference in temperature will cause condensation within the raceways and equipment; and if we don’t seal these as close as possible to the actual penetration point of the raceway, we will create a hazard. I’ve seen light fixtures inside coolers that have been filled with water as a result of ignoring this requirement, and water and electricity just don’t make a good match. I’ve seen some of the lights continue to operate, even though the lamps are submerged in water. Note that the required method of sealing the raceways or sleeves doesn’t have to be an explosionproof seal off, we just need to seal the raceway with an approved material that will fill the space. The material used should be intended and identified for use with electrical cables and equipment.
Photo 2. In the top photo the electricians have done a good job with making sure they have the proper length of free conductors, as noted on 300.14. In the lower photo you can see how adding extension boxes may be added and the code still would require 3 inches of free conductor outside the last extension.
Also in this section we cover Expansion Fittings. Raceways must be provided with these fittings where necessary to allow for expansion and contraction. One of the common locations for this issue is in larger buildings that have building separation expansion locations. Usually this is accomplished by the installation of a flexible raceway system installed at this location with a bit of slack to compensate for any movement. There are listed expansion fittings available. Use a bit of caution here: if using a listed fitting, make sure it is compatible with the raceway systems being installed.
Next we will skip to 300.10, Electrical Continuity of Metal Raceways and Enclosures. When using metallic wiring methods, they shall be metallically joined together into a continuous conductor and shall be connected to all boxes, fittings and cabinets to provide electrical continuity. The issue here is that we are often using the metal raceway system as our grounding path. Even if we are not, it still has the possibility of becoming energized and we must therefore ensure we have a good low-resistance path back to the location of the overcurrent device to insure it will operate in a timely fashion if needed.
Photo 3. In this photo we find a lack of lock nuts under the enclosure. In 300.10 the code requires raceways to connected to all boxes to provide for electrical continuity. In order to do this, we require lock nuts on both sides of an enclosure.
Securing and Supporting requirements are found in 300.11. In (A) we cover Secured in Place and find that raceways, cables assemblies, boxes, cabinets and fittings must be securely fastened in place. The code then goes into detail for installations done within ceiling assemblies; generally, the requirement here is that electricians need to install independent support wires for the electrical installations, which need to be supported at both ends of the support wires. It is further noted in the fire-rated and non-fire-rated installations that these support wires must be identified in order to show that the wires utilized for the support of our systems are independent of those installed to support the ceiling assembly. This identification can be done using one of several different methods, whichever is acceptable to the authority having jurisdiction. Locally, the simplest method we found was using the products specifically made to secure the support wires to the ceiling grid. That insured no additional stress was added to the ceiling system, and the products are made in a unique color which easily allows identification during the inspection process. Instead of covering 300.11(B) Raceways Used as Means of Support, I will state a general rule of thumb: raceways are not allowed to support other raceways. Please read this section as there are some applications that are permitted; however, I haven’t seen a system that allows raceways to support raceways. If you see an installation like this, ask questions until you are satisfied that the installation is properly done.
Photo 4. Article 300.15 requires boxes to be used for conductor splices when utilizing nonmetallic-sheathed cable; as you can see in the above photo, not everyone knows the code or follows it.
Next, we’ll group 300.12 and 300.13 into some simple language. First, raceway systems shall be continuous, which means no breaks between cabinets, boxes fittings or other enclosures or outlets. Second, the installed conductors shall not be spliced within a raceway, unless permitted in the areas of the code specifically listed in 300.13(A). Also covered here is the continuity of the grounded or neutral conductor of multiwire branch circuits; this is where we are sharing a neutral for more than one ungrounded conductor, which is permitted as long as the ungrounded conductors are on different phases. If we have these conditions, then we must make sure the neutral is continuous even if we take out a receptacle or other device. We do this by connecting the neutrals together with a twist-on wire connector and provide a short pigtail for connection to the receptacle. When we do this, if the receptacle is removed the neutral is still continuous and the circuit is complete; if we don’t do this, then when we interrupt the neutral or open it, the devices downstream from this location may see the potential between the other phase conductors, which is the phase-to-phase voltage of the system. This simple mistake will destroy equipment and also create a shock hazard if the other conductors of the multiwire circuit aren’t disconnected.
Photo 5. This photo shows an electrical installation that has had the conductors threaded through the raceways. Article 300.18 requires the raceways to be complete prior to conductor installation. The feed is from the left and the load is to the right, the top run goes to the disconnecting device, so we have both line and load in that run. The homeowners who did this installation put in a considerable amount of labor and injuries to get it this far; however, once we failed the inspection I think it might have led to other issues for the homeowners.
Length of Free Conductors at Outlets, Junctions, and Switch Points is covered in 300.14. This is a very important part of the code that needs to be checked during the rough inspection. As mentioned in previous articles, during the rough inspection we have to verify that we have proper make up and identification within each box for both the grounded and grounding conductors. The other thing we should be checking at the same time is the amount of free conductor; too little and it is very difficult to make the proper connections to the wiring devices being utilized. If we have too much free conductor, then we have a space issue when we try to push the device back into the box, which may lead to damaged conductors and a hazardous condition due to nicked insulation. The code is very clear on this subject: where we have a box that is less than 8 inches in any dimension, the amount of free conductor required is 6 inches from where the conductors emerge from the raceway or cable sheath. However, we don’t just stop with that, it also has to have 3 inches of free conductor past the face of the box, which is enough conductor for those situations where we might have to utilize deep boxes or extension boxes. With some of the devices, such as GFCIs, AFCIs, dimmers and occupancy sensors, the free area inside the box may become scarce. If you have locations where you know you may use a large device, be on the lookout and mention it to the electrician; you may just be saving him some trouble during the trim out process. Further into Chapter 3 we will cover the size of the box related to the size of device, but we will not be tempted to look ahead just yet.
The requirements for boxes, conduit bodies, or fittings are covered in 300.15. A box shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point unless not required in the 300.15(A) through (L). These twelve exceptions deal with specific types of wiring methods or products that have unique conditions which would not require a box; please review them to see what these conditions are, as I am not going to mention each of them here. Even though there are several exceptions, this is actually a pretty simple rule. Please review 300.16 for more information related to the use of boxes, conduit bodies or fittings.
Photo 6. These photos show conductor phase arrangements. Both are in metallic raceways, so the left photo shows a code compliant installation as per 300.20. In each run we have each phase, grounded and grounding conductor grouped in each raceway. In the photo to the right, we have a code violation.
I’m not going to cover 300.17 Number and Size of Conductors in Raceways, due to the fact that we will cover it in much more detail when we get to Article 310.
Skipping ahead to 300.18 Raceway Installations, this section is broken down into two parts. First, in (A) we have Complete Runs, and the requirement here is that raceways, other than busways, or exposed raceways having hinged covers, shall be installed as a complete run between outlet, junction, or splicing points prior to the installation of conductors. If you ever get on site and see someone threading conductors through pieces of raceway, please remember this section of the code. If the conductors can’t be pulled through a completed raceway installation, there is another problem which should be solved. Examples might be oversized conductors in the raceway, too many bends in the run, or other conditions that shouldn’t exist in a good code-compliant installation. The second section of 300.18 deals with Welding. Metal raceways shall not be supported, terminated or connected using a welding process unless specifically designed for welding. To date, I haven’t seen a system designed to be welded. However, that doesn’t mean I haven’t seen it attempted, as can be seen in one of the photos with this article. It should be pretty obvious that welding would cause rough, possibly sharp obstructions to the interior of the raceway, which would then cause damage to the conductors when they are being installed within the raceway system.
In vertical runs of raceways, we have to address the need to support the conductors from the pull of gravity. If you have a vertical run of 300 feet (approximately 30 stories) and you have four 500 kcmil copper conductors, the weight would be close to 1800 pounds. If these were simply terminated into the set screw lugs of a panelboard on the thirtieth floor with 1800 pounds of pressure pulling down, the panel would be destroyed. So how do we compensate for this? In 300.19, the code addresses how to support the conductors. First, we are to have a support at or as near as possible to the top of the raceway. Then, according to the size and type of conductors as noted in Table 300.19(A), we are required to add additional supports at certain distances. For our simple example above, we would need supporting points every 40 feet, or once every 4 floors. Please open your code book and read 300.19(C) for the options and alternate methods that can be used.
The last item I’m going to cover in Article 300 is 300.20 Induced Currents in Ferrous Metals Enclosures or Ferrous Metal Raceways. When installing alternating-current circuits in ferrous metal raceways or enclosures, you have the possibility of creating heat in the raceways through induction. To minimize this, the code requires that we group each of the phase conductors and the related grounded (neutral), and grounding conductor in each raceway. This will allow for cancellation of the magnetic fields created due to the nature of the alternating current in the conductors. If we don’t address this, we can have overheating of the conductors.
In 300.20(B), we have the method for installing Individual Conductors. The most common installation of this is mineral-insulated cables, which in larger sizes are one conductor per cable. When we have this type of installation, we are required to cut a slot between each cable connector when entering an enclosure, or to use an insulated wall properly sized for all the conductors. I have never seen the insulating wall option applied, so we generally see a slot cut between the connectors. This slot is nothing more than a saw blade width but remember that if entering an outdoor enclosure, doing this might compromise the outdoor rating of the enclosure.
Again, please take the time to open your code book and review the rest of Article 300. I have only touched on the most common areas which are used in various combination inspections. In the next article, we will start into Article 310, which is where we get into details on conductors.
Read more by Randy Hunter
Posted By Thomas A. Domitrovich,
Monday, September 16, 2013
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If there was ever a list of workhorse components in the electrical industry that are heavily used, sometimes abused, and called upon to perform over and over again safely and reliably, I would have to say that 15-A and 20-A receptacle devices rank high on that list. Many people interface with these devices on a daily basis. They are found in all kinds of locations from harsh environments to clean rooms. Because these devices are so heavily utilized by the electrical contractor and are inspected in so many different industries, it’s worth a peek into the world of receptacles and a journey back to basics.
CODES AND STANDARDS
Some people may think the world revolves around codes and standards but the fact is that many products, in addition to revolving around meeting customer wants and needs, do. The following documents are pertinent to our discussion on receptacles:
- UL 498, Attachment Plugs and Receptacles, is the UL document that governs the performance requirements for receptacles and attachment plugs. We’ll talk more about this document later.
- NFPA 70, National Electrical Code, is the installation requirements that include articles and sections with specific requirements for the installation of receptacles.
- CSA C22.2, General use receptacles, attachment plugs, and similar wiring devices, is the Canadian standards document that governs the performance requirements for receptacles and attachment plugs and similar wiring devices for use in Canada.
- Federal Specification WC596, General Specification for Connector, Electrical, Power. This document includes additional MIL Spec references and testing requirements.
NEC 2011 defines a receptacle as a "contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke.” We’ll have to review the parts of a standard receptacle to really understand some of this definition as I’m sure that the reference to yoke above is more than likely not the yoke you had with toast and coffee this morning. Understanding the parts of a receptacle is important as they are referenced in various sections of the Code. The term yoke is one of those that we use frequently but for which there is no formal definition. Rather than assume we all know what a yoke is, let’s define it. In general the yoke, sometimes used interchangeably with the term strap, is a mounting means for a wiring device. The yoke of a receptacle is the frame, the metal portion of the receptacle that is used to mount a device to the outlet box. (Reference figure 1.) While not prevalent, there are non-metallic yokes. The device depicted in figure 1, has two contact devices on a single yoke.
As an example of how important it is to understand the term yoke, let’s look at the language of Section 210.7 of NEC 2011.
"210.7 Multiple Branch Circuits. Where two or more branch circuits supply devices or equipment on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided at the point at which the branch circuits originate.”
For the device in figure 1, only one branch circuit would supply both contact devices without modification as both contact devices are electrically connected. If the tabs on each side of the receptacle are removed from this device, the upper single contact device and lower single contact device are cleanly separated electrically from each other. In this case, you may have two branch circuits supplying this single yoke, with one branch circuit feeding the top single contact device and the other supplying the lower single contact device. Both of these single contact devices share a single yoke. Hence, as per Section 210.7, the two branch-circuit overcurrent devices must have a means to simultaneously disconnect the ungrounded conductors.
Another example of the use of yoke in the Codecan be found in Section 220.14, "Other Loads – All Occupancies,” where the minimum load for each outlet for general-use receptacles and outlets are calculated. Section 220.14(I) Receptacle Outlets states the following:
"(I) Receptacle Outlets. Except as covered in 220.14(J) and (K), receptacle outlets shall be calculated at not less than 180 volt-amperes for each single or for each multiple receptacle on one yoke. A single piece of equipment consisting of a multiple receptacle comprised of four or more receptacles shall be calculated at not less than 90 volt-amperes per receptacle. This provision shall not be applicable to the receptacle outlets specified in 210.11(C)(1) and (C)(2).”
The term yoke is used 20 times in NEC 2011; it is important to understand what a yoke is so as to apply the Codeaccurately.
On the standards front, UL 498 is the standard for receptacles that defines the many performance based tests conducted on these devices. We will explore, at a high level, these tests to which a receptacle must submit.
Standard Receptacle Product Performance Criteria
Product test standards thrive on performance based testing; they seek to create the tests and environments to which the devices will be subjected in their application. Some of the key performance test requirements for receptacles include the following:
- Retention of blades: After ten insertions, not to exceed 40 lb of force, of a standard steel blade plug gauge, the receptacle must be able to hold (retain) a polished steel 2 bladed plug gauge without holes (the grounding blade removed) against a 3 lb force for 1 minute. The receptacle must release a polished steel 3 bladed plug gauge with holes at no more than 15 lb of force.
- Current overload: To pass this test, the same test samples from the previous test are utilized and must not exhibit any electrical or mechanical failure, pitting or burning of the contacts, that would affect the intended function. The test sample device is subjected to 100 insertions & removals of a mating plug making and breaking dc current through a resistive load at 150% of device rating. The blade of the attachment plug is to mate with the contact of the receptacle for not more than 1 second during each cycle.
- Temperature rise: After the previous current overload test, the same samples are subjected to this temperature rise test. Strategically placed thermocouples help to ensure the test subject passes this test which requires that the contact temperature rise of a flush or self-contained receptacle shall not be more than 30°C (54°F) when the receptacle is carrying its maximum rated current.
- Repeat blade retention: For those test samples experiencing the previous temperature rise test, they must additionally pass the Blade Retention test described in item 1 above.
- Resistance to arcing: The outlets that were subjected to the 100 cycles of operation in the Overload Test described in item 2 above must perform acceptably when subjected to an additional 150 cycles of operation under the overload test conditions following the temperature test and the repeated retention of blades test. There is also a dielectric test built into this test; 1500 volts for 1 minute to ensure the integrity of the device.
I think it is worth stopping here for a moment to reflect on this specific test as it is a good example of a redundancy that is not unique in this specific UL standard. In this case, the test samples used are not new or fresh out of the box. These samples have experienced an overload test as well as the temperature and repeated retention of blades tests. We’ll see more of this redundancy as we move into the Hospital Grade and other similar products. First, let’s continue looking at what a receptacle must endure as part of this UL standard performance test requirements.
- Terminal strength: The standard 3-prong steel test gauge is inserted 10 times and the maximum insertion force should not exceed 40 lbf. If the receptacle has a breakoff tab, it is removed prior to the conditioning. After conditioning, each terminal is wired with 12 AWG solid copper wire by applying 14 in-lbs of tightening torque. The wire is stripped to the length specified in the manufacturer’s installation instructions. Wire-binding screw terminals are wired by placing the stripped conductor under the screw head and wrapping it ⅔–¾ turn around the screw. Pressure-wire terminals are wired by inserting the stripped conductor into the terminal. The terminal screw is then torqued, loosened and retorqued. Following the last torqueing, each terminal is to be subjected to a straight 20-lbf (89-N) pull applied to each wire for 1 minute perpendicular to the plane of the back cover of the receptacle; the wire shall remain in place. Following this pull, the receptacle must be able to hold (retain) a polished steel 2 bladed plug gauge (without holes in the blades and without ground) against a 3 lb force for 1 minute. The receptacle must release a polished steel 3 bladed plug gauge (with holes in the blades) at no more than 15 lb of force.
- Grounding pin retention: In these tests, the grounding pin is the focus. It is subjected to various situations including a weight of 5 lbs located 6 inches from the outlet face, a 360 degree rotation of a grounding pin during which time the continuity must be maintained. After the receptacle is subjected to these tests, the ground contact must retain a pin being subjected to a 4 oz. and 2 oz. weight depending upon the dimension of the pin.
- Fault current: For this test, the receptacle is subjected to a through fault current of 1,000 amperes downstream of a 15-A or 20-A circuit breaker. After the receptacle experiences this fault current, it must retain its integrity as demonstrated by a continuity check after removing and reinserting the attachment plug.
- Dielectric voltage withstand: For tamper-resistant receptacles, a dielectric test is performed to determine the effectiveness of a device’s insulation. In this case, a potential equal to twice the rated voltage of the receptacle plus 1,000 volts is applied between live parts of opposite polarity and between live parts and grounded or dead metal parts and must not exhibit any arcing or breakdown.
- Mold stress relief: Unwired receptacles are subjected to 70oC for 7 hours and after being allowed to cool, measurements are made where there shall not be any warping, shrinkage or other distortion that results in the device not performing as expected.
- Dielectric voltage withstand (repeated): After the above mold stress relief test, the same test specimens are again subjected to the dielectric voltage withstand tests described above in item 9.
- Assembly security: This test is quite grueling in that the subject receptacle must endure a 50 lb force through extra-long blades inserted into the receptacle and directly on the back of the receptacle.
The above performance tests are just a taste of what a receptacle must pass to obtain the UL label. These tests help ensure the device will safely perform when called upon.
Hospital Grade Product Performance Criteria
In addition to these basic performance tests, UL 498 includes supplements for product requirements addressing other application needs. One such supplement is that for Hospital Grade Devices; supplement SD includes nine additional tests that make hospital grade receptacles what they are. The following additional tests are a taste of what a Hospital Grade receptacle requires:
- Abrupt plug removal: A test plug with brass blades that is attached to a 10 lb weight is inserted into a receptacle. The weight is dropped from 24″ a total of eight times in an effort to abruptly remove the plug from the receptacle. After the eighth removal of the plug, the receptacle shall not experience any breakage that exposes live parts, be able to be mated to a standard plug, retain a 3 lb weight using a standard 2 prong plug (without ground) and retain a 4 oz. undersized ground pin.
- Grounding contact temperature: Using the same devices previously tested above, the acceptability of the grounding path in a receptacle shall be demonstrated by a temperature rise not exceeding 30°C (54°F) when subjected to these tests. The test subjects eight receptacles previously tested to a continuous current of 25 amperes for 1 hour and then 22 amperes until equilibrium is reached after being wired in series through the grounding conductor path.
- Grounding contact resistance: The same devices that experienced the past two tests are again subjected to yet another. This time the resistance between the mated attachment plug grounding terminal and receptacle grounding terminal shall not exceed 0.01 ohms.
- Fault current test: The test subjects that have been previously tested in the above three tests are then subjected to the standard fault current tests. The grounding path must retain its integrity.
- Grounding contact overstress: After an oversized steel pin (0.203 in.) is inserted 20 times into each ground contact, each ground contact must retain a standard sized (0.184 in.) polished steel pin against a 4 oz. force for 1 minute.
- Terminal strength: This is similar to the terminal strength test that is part of the standard receptacle testing criteria except for the fact that the terminals are disassembled, assembled and then torqued three additional times with a maximum tightening torque of 14 lbf-in (1.6 N-m) instead of the standard 14 lbf-in (1.6 N m) for a #8 screw.
- Assembly security: The assembly security test of the standard receptacle which is performed with a 50 lb force is performed with a 100 lb force.
- Impact: Receptacles are installed in a metal outlet box with a metal faceplate with the outlet facing up. Then a 5 lb weight is dropped from a height of 18 inches impacting the center of the receptacle outlet. There shall be no breakage that impairs the function of the receptacles or the insertion of a plug.
- Increased mold stress relief: Unwired receptacles are subjected to 90oC for 7 hours and after being allowed to cool, measurements are made where there shall not be a change in any dimension greater than 10 percent, nor any warping creating an opening greater than 1/32 in. (0.79 mm) in any butt joint forming the enclosure of each receptacle.
These hospital grade receptacles, after passing all of the additional tests, must be marked with the phrase "Hospital Grade” or "Hosp. Grade” and with a green dot.
Fed Spec Product Performance Criteria
Yet another type of device that confuses some when found in the field is the Fed Spec receptacle device. Just as in the Hospital Grade receptacles discussed above, Federal Specifications pile on an additional number of tests to the standard receptacle tests. The following additional 9 tests are a taste of what Federal Specification WC596 requires:
- Gripping – Power Blade – Grounding Blade: In this test, an oversized blade is inserted and removed 20 times into the current-carrying contact (a 0.075 in. thick blade instead of a 0.06 in. thick blade). Then each current-carrying contact must retain a less than standard thickness steel blade secured to a 1.5 lb weight for 1 minute (a 0.055 in. thick steel blade instead of the 0.06 in. thick blade). A similar test is done for the ground blade with modifications.
- Terminal Strength: This test is similar to the Hospital Grade test above. The terminal is tightened 5 times on to a minimum and maximum wire of 14 – 10 AWG and then tested by hanging a 20 lb weight from the wire for 1 minute.
- Overload 200% AC: A plug is inserted and removed from the receptacle 250 times as compared to the 100 times of UL 498, before conducting a 200% rated current test. UL 498 only requires this test to be run at 150% of rated current.
- Temperature Rise: Strategically placed thermocouples help to ensure the test subject passes this test which requires that the contact temperature rise of a flush or self-contained receptacle shall not be more than 30°C (54°F) when the receptacle is carrying 20 amperes for both 15-A and 20-A receptacles.
- Repeat Blade Retention: This repeated blade retention test is performed after the temperature rise test as is done for all receptacles.
- Dielectric Voltage Withstand: A potential equal to twice the rated voltage of the receptacle plus 1,000 volts is applied between live parts of opposite polarity and between live parts and grounded or dead metal parts and must not exhibit any arcing or breakdown.
- Insulation Resistance: The insulation resistance, when measured at various points on the receptacle, shall not be less than 100 megohms.
- Heat Resistance: Unwired receptacles are subjected to 85oC for 2 hours and after being allowed to cool, the device shall show no evidence of mechanical or electrical failure, flow, or critical softening of sealing compounds, or softening or distortion of parts.
- Assembly Security: This test is similar to that which is performed for a Hospital Grade receptacle. The receptacle must endure a 100 lb force through extra-long blades inserted into the receptacle as well as a 50 lb force to the back bridge of the receptacle.
The above should provide some insight to the differences between a standard receptacle, a Hospital Grade receptacle, and a Fed Spec device. The only other type not discussed above that is included in UL 498 Supplement SE and ones you may frequently see are the Weather-Resistant receptacles. These devices must also include corrosion-resistant, cold impact, accelerated aging, and resistance to ultraviolet light characteristics. They are intended to be installed in appropriate enclosures suitable for the application. They are not meant to be installed with direct exposure to water. Just as an example, all wire-binding screws and terminal pressure plates must be copper alloy or stainless steel having a minimum of 16% chromium content. These devices receive special attention to the materials with which they are constructed, as well as some additional tests to temperature cycling, UV light, and more.
RECEPTACLE CONFIGURATIONS, CLASSIFICATIONS, AND GRADES
If you have ever walked down the plug and receptacle aisle of your supply house, you may have left amazed at how many different variations of these devices there are. Plus, there are existing plugs and receptacles that weren’t on those shelves you were looking at. Just as in any product, there are reasons for this variety and there are standards that govern their configuration and application.
A great place to start to understand all of the available configurations is to review NEMA publication WD6, Wiring Devices—Dimensional Specifications. This free download from the www.nema.org website is a great resource to get your arms around the breadth of solutions that are available in the receptacle basket. All of the different NEMA configurations are clearly identified in NEMA WD6, but what is not included is an explanation of where you will typically see each type of configuration. If you are like me, you interface with a very limited range of receptacle types; so in hopes to convey the differences between these configurations, beyond what the NEMA document provides, I’ve assembled Table 1, which focuses only on straight blade available configurations.
The NEMA designations identify the blade configurations for receptacles with each NEMA receptacle configuration having a corresponding plug. The WD6 document includes images of each configuration for your reference. These different blade configurations help ensure the designated loads are only plugged into their designated receptacles. The changes in configurations occur by voltage rating and sometimes by grounding for each of the available ampacity devices. The available configurations for 15-A receptacles, for example, have different receptacle blade configurations for the various voltages including 125-V (grounding and non-grounding); 250-V (grounding and non-grounding); 277-V; 347-V; 3-Phase 250-V; and 125V/250V. Just to reiterate an im-portant fact, the various NEMA configurations ensure that a specific load that requires a specific voltage is not mistakenly plugged into the wrong receptacle. There are also corresponding locking types not discussed here.
The designations do not stop there as in addition to the above NEMA configurations, manufacturers offer different grades of products; some driven by product standards and others driven by market requirements. These grades include but are not limited to the following:
- Standard Grade
- Specification Grade
- Construction Grade
- Hospital Grade
- Industrial Grade – beefy, heavy, meant for use in the plant. Thicker metals
- Commercial Grade
Those grades not governed by the UL standard have qualities that the manufacturer included to meet needs of various target markets. For example, having a strap of brass rather than steel, contacts of a greater thickness for less heat rise, more contact wipes on the blades which gives a better connection are all ways a manufacturer may enhance their product. These go above and beyond the bare minimum product standards.
Just as with any product, these devices too can be applied incorrectly in the field; it’s important to pay attention to where and how these devices are being installed. Care should be taken when landing wires on terminals and when pushing receptacles back into the outlet box. Make sure the environmental condition fits the rating of the device. If you are installing both the plug and receptacle for a specific load, ensure you are paying close attention to all of the code requirements surrounding the installation. The act of cutting off the plug from appliances and installing your own, not only may violate the UL Listing of the product you are modifying, but it also may create an unsafe installation.
- NEMA WD6, Wiring Devices—Dimensional Specifications, http://www.nema.org/Standards/Pages/Wiring-Devices-Dimensional-Specifications.aspx#download
- NEMA Document, Protection of Receptacle Outlets in Wet Locations According to the National Electrical Code,http://www.nema.org/Standards/Pages/Protection-of-Receptacle-Outlets-in-Wet-Locations-According-to-the-National-Electrical-Code.aspx#download
- NEMA WD1, General Color Requirements for Wiring Devices,http://www.nema.org/Standards/Pages/General-Color-Requirements-for-Wiring-Devices.aspx#download
- "UL Listed Hospital Grade Receptacles, The differences between grades” http://www.ul.com/global/documents/offerings/perspectives/regulators/technical/ul_HospitalGradeReceptacles.pdf
- UL White Book, RTDV, RTRT
We’ve all interfaced with the standard 15-A and 20-A receptacle. It is indeed one of those devices that is heavily used, sometimes abused, and must perform over and over again safely and reliably. As you can see above, the standard for these devices reflects the awareness of this intended use. Hopefully this discussion has enlightened us all to the world of the incredible receptacle..
As always, keep safety at the top of your list and ensure you and those around you live to see another day.
Read more by Thomas A. Domitrovich
Posted By Keith Lofland,
Monday, July 01, 2013
Updated: Wednesday, June 19, 2013
| Comments (3)
A few of years ago, in an attempt to get rid of an old refrigerator, my Dad placed this working, reliable refrigerator at the curb with a sign saying, "Free Refrigerator. Good Working Condition. Just Take It!” The refrigerator sat at the curb for a week with no takers. Being the shrewd guy he was, my Dad decided to take a different tack with this unwanted appliance. He took the "Free” sign down and replaced it with a sign saying, "Refrigerator – $50.” The next day, someone stole the refrigerator!
The words and phrases we use to describe situations and things can alter the values for different people on different things. In that vein, we find ourselves once again on the threshold of a new and revised National Electrical Code® (NEC) with new and revised words and phrases, in an attempt to keep up with our ever-changing electrical industry.
According to the National Fire Protection Association (NFPA), there were 3745 proposals submitted to NFPA recommending changes from the 2011 NEC to the 2014 NEC. In addition to these proposals, there were 1625 comments submitted concerning the NEC Code-Making Panels’ responses to these proposals. In this article, we will look at some of the more noteworthy changes that occurred in the 2014 edition of the NEC. This article should serve as foreshadowing to IAEI’s Analysis of Changes, 2014 NEC textbook and PowerPoint training material. ThisAnalysis training material should be available by the time you arrive at your IAEI Section Meetings this fall.
Revision: 600 Volts to 1000 Volts Threshold
There were 120 proposals submitted to raise the 600-volt threshold in the NEC to 1000 volts in the 2014 NECCode cycle. This resulted in numerous changes throughout the NEC from 600 volts to 1000 volts. These proposals were submitted by the High Voltage Task Group (HVTG), which was appointed by the NEC Correlating Committee. For the 2014 NEC, the work of the HVTG had the primary focus of raising the voltage threshold in the NEC from 600 to 1000 volts. Today, emerging technologies such as wind electric generating systems are operating at just over the 600-volt threshold. Solar photovoltaic (PV) systems are currently being installed at dc voltages over 600 volts up to and including 1000 volts, 1200 volts, 1500 volts, and 2000 volts dc
Chapter One – General
New: Article 100 Definition: Retrofit Kit
A new definition of retrofit kit was added to Article 100 as this term applies to LED listed retrofit kits used for luminaires and signs, as referenced by new requirements in Articles 410 and 600. Extensive upgrades are underway in the sign and lighting industries to achieve greater energy efficiency in signs and luminaires by replacing in-place illumination systems with light emitting diodes (LED) technology. This will incorporate field modifications of signs or luminaires. Field modifications of utilization equipment usually require a field evaluation by a qualified nationally recognized testing laboratory (NRTL). Testing laboratories, such as Underwriter’s Laboratories (UL), have developed protocols for these field conversions. When installed within the testing laboratory parameters, these field conversion retrofit kits do not compromise the safety profile of the listed sign or luminaire.
New: 110.21(B) Field-Applied Hazard Markings.
A new sub-level (B) was added to 110.21 for Field-Applied Hazard Markings, to add specific requirements for warning labels and similar markings where required or specified elsewhere in the Code. The NEC contains several requirements for labels to be installed on wiring methods and equipment. These required labels or markings typically include one of the following hazard commands: DANGER, WARNING, or CAUTION. With no standardization for labeling, the results were inconsistent application of these NEC rules. This new requirement will incorporate consistent uniformity to rules where additional direction and guidance were needed. These markings, signs or labels should meet ANSI Z535.4 for suitable font sizes, words, colors, symbols and location requirements. Coordinated companion proposals and comments were submitted where the caution, warning, and danger markings or signs are required throughout the NEC with reference to this new requirement in Article 110.
New: 110.25 Lockable Disconnecting
Means in Article 110.
A new 110.25, Lockable Disconnecting Means, was added to the 2014 NECto deliver a one-stop location providing consistent requirements for a lockable disconnecting means. Forty-six companion proposals were submitted throughout the NEC to reference this new requirement and to send users of the Codeback to one location for lockable disconnecting means requirements. These companion proposals were submitted by a Usability Task Group assigned by the Technical Correlating Committee (TCC) to look at the numerous locations in the 2011 NEC that referenced lockable disconnecting means requirements.
New: 110.26(E)(2) Dedicated
Equipment Space for Outdoor Installations.
A new provision for dedicated equipment space was added at 110.26(E)(2) for outdoor installations of electrical equipment. This new requirement now calls for the same basic dedicated equipment or electrical space for outdoor installations that has been in effect for indoor installations at 110.26 since the 1999 edition of the NEC. Outdoors, some of the same "equipment foreign to the electrical installation” is often present such as gas piping, water piping, mechanical refrigeration lines, irrigation equipment, phone and internet equipment, compressed air lines, and other non-electrical equipment. When installed in the dedicated electrical space, these foreign items impede access to the electrical equipment. This is true regardless if the electrical equipment is installed indoors or outdoors. This space above and below the electrical equipment should be dedicated to the electrician for the installation of electrical conduits, cables, etc., in and out of panelboards, switchgears, etc.
Photo 1. Dedicated equipment space is now required for outdoor electrical equipment, not just for indoor equipment.
Chapter Two – Wiring and Protection
New: 210.8(A)(10) GFCI Protection for Dwelling Unit Laundry Areas.
Dwelling unit laundry areas will now require GFCI protection for all 125-volt, single-phase, 15- and 20-ampere receptacles installed in a laundry room. The presence of a laundry room sink is no longer the driving factor of whether GFCI protection is required or not. As the requirements for GFCI protection has been expanded throughout the NEC over the last fifteen code cycles, the number of electrical shock incidents related to consumer products has continued to decline over that time. Increased usage of GFCI protection for personnel at receptacles of residential homes is a highly effective means of further reducing the potential for electrical shock hazards.
New: 210.8(D) GFCI for Kitchen Dishwasher Branch Circuit.
A new provision was added which will now require GFCI protection for all outlets that supply dishwashers installed in dwelling units. This would include a receptacle outlet or a hard-wired outlet for a dishwasher. Modern electronically controlled dishwashers have different failure modes than their electromechanical ancestors. End of life for today’s dishwashers can result in increased risk of electrical shock, which can be mitigated by providing GFCI protection for outlets supplying dishwashers.
Photo 2. Dwelling unit dishwashers will now require GFCI protection.
Revision/New: 210.12(A)(1) thru (A)(6) AFCI Protection for Dwelling Units.
AFCI protection methods were expanded and language was put into a list format. The list of rooms in a dwelling unit that will now be required to be provided with AFCI protection was expanded to include kitchens and laundry areas. AFCI protection is now required for all 120-volt, single-phase, 15- and 20-ampere branch circuits supplying not just outlets but also devices that are installed in the list of rooms requiring AFCI protection at 210.12(A). The first two exceptions were revised to positive language and put into a list format of six provisions for providing AFCI protection to the branch circuit(s) involved. Provisions for the use and installation of outlet branch circuit (OBC) AFCI devices were greatly expanded. The three existing Informational Notes were revised and updated for clarity.
New: 210.17 Electric Vehicle Branch Circuit.
New provisions were added to require outlet(s) installed for the purpose of charging electric vehicles to be supplied by a separate branch circuit with no other outlets. A new Informational Note was also added to point users of the Code to 625.2 for the definition of an electrical vehicle. It should be noted that this new requirement does not demand that an outlet(s) for the specific and sole purpose of charging EV equipment be installed. This new requirement simply states that where such EV charging outlet(s) are installed by choice, these outlet(s) must be supplied by a separate or individual branch circuit with no other outlets. This new provision for EV charging will go a long way in ensuring that EV charging can be completed safely and effectively without overloading an existing branch circuit. Along these same lines, a new provision was also added at 210.52(G) requiring a receptacle to be installed for each car space of a multi-car garage.
Revision: 250.66(A) and (B) Connections to a Rod, Pipe, or Plate and Concrete-Encased Electrode(s).
As far as sizing a grounding electrode conductor, the requirements are the same in the 2014 NEC as they were for the 2011 NEC. Explanatory-type language and plural text were added to 250.66(A) and (B) to clarify that the sole connection provisions of these subsections pertain to the types of electrodes in these subsections, and the sole connectionsizing provisions are not forfeited if more than one of the specified types of electrodes involved are present.
New: Table 250.102(C) Sizing Bonding Conductors and Jumpers.
A new Table 250.102(C) entitled, "Grounded Conductor, Main Bonding Jumper, System Bonding Jumper, and Supply-Side Bonding Jumper for Alternating-Current Systems” was added to the 2014 NEC to be used for sizing grounded conductors, main bonding jumpers, system-bonding jumpers, and supply-side bonding jumpers, rather than Table 250.66. References to this new table were revised throughout Article 250. This new Table 250.102(C) and the included notes to the table will apply to other fault-return carrying conductors if the supply conductors do not have overcurrent protection on the supply side. Table 250.122 would continue to be used for sizing fault-return carrying conductors, such as equipment grounding conductors, if the supply conductors have overcurrent protection on the supply side.
Chapter Three – Wiring Methods
New: 300.38 Raceways in Wet Locations Above Grade.
A new section was added to Part II (over 1000 volts, nominal) of Article 300 to indicate that the interior of raceways installed in wet locations above grade are now considered to be a wet location. This will bring aboveground installation requirements for over 1000 volts consistent with the requirements in 300.9 for 1000 volts and under.
Revision/New: 310.15(B)(3)(c), Exception and Table 310.15(B)(3)(c) Raceways and Cables Exposed to Sunlight on Rooftops.
The title and parent text at 310.15(B)(3)(c) were revised for clarity from "Circular Raceways Exposed to Sunlight on Rooftops” to "Raceways and Cables Exposed to Sunlight on Rooftops.” The basic provisions for applying an ambient temperature adjustment correction factor where any type of raceway (not just circular raceways) is exposed to direct sunlight on or above rooftops have not changed. Provisions for cables installed on or above rooftops have been added as well. Cables were subject to these ambient temperature adjustment correction factors in the past, but the language indicated that the cable(s) had to be installed in a raceway. A new exception was also added that will allow the employment of Type XHHW-2 conductors, which is a thermoset insulated conductor, to be installed in raceways or cables on rooftops without having to apply an ambient temperature adjustment correction factor for these conductors.
Revision/Deletion: 310.15(B)(7) Sizing 120/240-Volt, Single-Phase Dwelling Services and Feeders.
The previous Table 310.15(B)(7) has been deleted entirely. The parent text at 310.15(B)(7) has been revised and broken up into four level 1 list items. Rather than use previous Table 310.15(B)(7) for sizing service conductors and the main power feeder for dwelling units, the user of the Code is left with a calculation to perform. The ampacity values found at Table 310.15(B)(16) can be reduced by 17 percent (not less than 83 percent of the service or feeder rating), which will require the circular mils properties of Table 8 in Chapter 9 to be brought into the now required calculation. A new Informational Note will take users of the Code to Example D.7 in Annex D for an example of how to perform this dwelling unit service and feeder calculation.
Revision: 314.27(A)(1) Boxes at Vertical Surface Luminaire or Lampholder Outlets.
The title of 314.27(A)(1) was changed from "Wall Outlets” to "Vertical Surface Outlets” as not all vertical surfaces where luminaire or lampholders are mounted are necessarily in a wall. Text was also revised in the subsection and in the exception reflecting this vertical surface vs. wall surface fact. New language was added to reflect that a luminaire or a lampholder can be mounted "on” a vertical surface as well as "in” a vertical surface.
New: Article 393 Low-Voltage Suspended Ceiling Power Distribution Systems.
A new article for Low-Voltage Suspended Ceiling Power Distribution Systems was added to address low-voltage Class 2 ac and dc volt equipment connected to ceiling grids, and walls built specifically for this type of power distribution system. The growing interest in alternative energy sources (e.g., photovoltaics, wind turbines, batteries, fuel cells, etc.) and the proliferation of low-voltage, low-power devices (sensors, LV lighting, IT equipment, AV equipment, etc.), has created a significant need for adequate language supporting the practical safeguarding of circuits and electrical equipment operating at 30 volts ac, or 60 volts dc, or less. This new article addresses equipment with similar characteristics to track lighting, but includes the wiring and power supply requirements as well. It also provides the specific requirements for the safe installation of low-voltage, power-limited power distribution, providing power to lighting and non-lighting loads.
Photo 3. Boxes can be mounted on vertical surfaces that are not necessarily considered to be a wall
Chapter Four – Equipment for General Use
New: 400.7(A)(11) Uses Permitted for Flexible Cords and Cables.
In addition to the uses permitted in the previous edition of the Code, a new provision was added to the 2014 NEC allowing a flexible cord to be used between an existing receptacle outlet and an inlet, where the inlet provides power to an additional single receptacle outlet. Part of this new allowance requires the wiring interconnecting the inlet to the single receptacle outlet to be a Chapter 3 wiring method. The inlet, receptacle outlet, and Chapter 3 wiring method, including the flexible cord and fittings, must be a listed assembly specifically for this application. This new provision is designed to allow newer and identified products primarily used for flat-screen televisions mounted on a wall. These products come as a listed assembly designed for this purpose.
Revision/New: 404.2(C) Grounded Conductor at Switches Controlling Lighting Loads.
Requirements and exceptions for the grounded conductor at switching locations have been revised into positive text and rearranged into a list format. This subsection and the exception were revised for the 2014 NECto incorporate the exception (with two conditions) into positive text and to arrange the conditions to which a grounded conductor would not be required at the switch location into a simpler-to-use list format. Five new conditions were added along with the existing two conditions described in the previous exception. Some of these locations that are now incorporated into 404.2(C) included switch locations that do not serve a habitable room or bathroom, such as a closet light switch or a door-jam switch, where an occupancy sensor or other electronic device is highly unlikely to be installed. A room or area where two 3-way and/or 4-way switches are installed to serve the same area is another location where a grounded conductor is not required at every one of these switch locations.
Revision: 406.9(B)(1) Extra-Duty Covers at 15- and 20-Ampere Receptacles at Wet Locations.
For the 2014 NEC, all 15- and 20-ampere, 125- and 250-volt receptacles installed in a wet location still must have an enclosure and covers that are weatherproof whether an attachment plug cap is inserted or not. A revision now requires all enclosures and covers installed in wet locations for 15- and 20-ampere, 125- and 250-volt receptacles to be listed and of the "extra duty” type, not just boxes supported from grade. This requirement is now also required at dwelling units as well. The requirement for weather-resistant type receptacles in wet locations is still applicable in the 2014 NEC. This change also provoked changes at 590.4(D)(2) for extra duty covers for all 15- and 20-ampere, 125- and 250-volt receptacles installed at temporary installations in a wet location.
New: 422.23 GFCI at Tire Inflation and Automotive Vacuum Machines.
A new section was added in Article 422 to require ground-fault circuit-interrupter (GFCI) protection for all tire inflation machines and automotive vacuum machines provided for public use. Tire inflation and automotive vacuum machines are generally located in commercial establishments, such as convenience stores and car wash areas, where they are heavily used by the general public. This type of public-use equipment is typically exposed to the elements and is often misused to the point of abuse. This type of equipment will typically be used outdoors in rain, snow, and puddles of accumulated standing water. Abused, deteriorated electrical equipment combined with a wet environment are recognized as contributing factors that increase the risk of an electrical shock hazard.
Photo 4. GFCI protection is now required for all tire inflation and automotive vacuum machines provided for public use.
New: 440.9 Grounding and Bonding at Outside AC Equipment.
A new section 440.9 was added to the 2014 NEC that now requires a wire type equipment grounding conductor, as specified in 250.118(1), to be provided in the outdoor portion of the raceway at outdoor air-conditioning and refrigeration equipment when the wiring method consists of liquidtight flexible metal conduit (LFMC) or electrical metallic tubing (EMT). The addition of this new requirement will help prevent electrocution and shock hazards from occurring around air-conditioning and refrigerating equipment located outdoors. This more specific and intentional type of equipment grounding conductor has the potential to maintain a grounding and bonding connection even under duress.
Revision/New: 445.11 Marking at Generators.
A new manufacturer’s marking provision was added requiring indication as to whether or not the generator neutral is bonded to the generator frame. This new neutral bonding provision goes further to require additional marking to indicate whether the generator neutral is bonded to the generator frame, whenever the bonding of a generator is modified in the field. In order to determine if a generator is a separately derived system or not, installers, enforcers, and users of the Code must be able to determine if the neutral conductor of the generator is bonded to the generator frame. This will allow for the selection of appropriate transfer equipment and implement applicable wiring method requirements.
New: 445.20 GFCI Protection for Receptacles on 15-kW or Smaller, Portable Generators.
A new section entitled, "Ground-Fault Circuit-Interrupter Protection for Receptacles on 15-kW or Smaller, Portable Generators,” was added in Article 445. This new provision will now require all 125-volt, single-phase, 15-and 20-ampere receptacle outlets, that are a part of a 15-kW or smaller, portable generator to be either equipped with GFCI protection integral to the generator or receptacle, or be capable of rendering the 125-volt, single-phase, 15-and 20-ampere receptacle outlets unavailable for use when the 125/250 volt locking-type receptacle is in use. This new requirement also indicates that if the generator does not have a 125/250 volt locking-type receptacle, this GFCI requirement is not applicable.
Photo 5. Indication as to whether or not the generator neutral is bonded to the generator frame and GFCI protection is required for portable generators.
Chapter Five – Special Occupancies
Deletion: 517.2 Definitions – Emergency System.
The term emergency system has been eliminated from Article 517, leaving only essential electrical system with the three separate branches: the critical, life safety and the equipment. The diagram in Figure 517.30, No. 1 has been re-worked to reflect these changes as well. In an effort to correlate the requirements of the NEC and, in particular, Article 517 with NFPA 99, Health Care Facilities Code, section 517.30(B) was re-organized in regard to the essential system of a hospital. This action eliminated references to the emergency system as this is not addressed to NFPA 99. In incorporating the changes made to correlate with NFPA 99, emergency system is no longer used in Article 517. This removes major confusion resulting from the previous use of the word "emergency” in similar, yet sometimes quite different, ways in Article 517 and in Article 700.
Revision/New: 517.18(B); 517.19(B); and 517.19(C) Health Care Facilities – Number of Receptacles.
The minimum number of receptacles required for specific areas of a health care facility was increased to align the NEC with NFPA 99, Health Care Facilities Code. The minimum number of receptacles required by 517.18(B) for general care area patient bed locations was increased from four to eight receptacles. The minimum number of receptacles required by 517.19(B) for critical care area patient bed locations was increased from six to fourteen receptacles. A new 517.19(C) was added requiring a minimum number of thirty-six receptacles in an operating room.
Revision: 590.4(J) Supports for Cable Assemblies and Flexible Cords and Cables.
Cable assemblies and flexible cords installed as branch circuits or feeders are now prohibited from being installed or laid on the floor or on the ground for temporary installations, such as construction sites. This rule does not apply to extension cords.
Chapter Six – Special Equipment
New: Article 646 Modular Data Centers.
A new article for Modular Data Centers was added in Chapter 6 to draw a distinction between data centers that currently fall under the scope of Article 645, Information Technology Equipment. Modular Data Centers (MDCs) are an important emerging trend in data center architecture. Their construction, installation and use result in a unique hybrid piece of equipment that falls somewhere in-between a large enclosure and a pre-fabricated building. The contained equipment in the enclosures or prefabricated buildings would be fully customizable and scalable to provide data center operations but, typically, would not be permanently installed. Article 645 is only applicable to installations that meet the criteria of 645.4. Otherwise, Article 645 would not be applicable to these products, and the other articles of the Codewould have to be applied. However, it is not always obvious which requirements in the NEC are applicable, or how they should be applied given the complexity, customization, and scalability of modular data centers. This article identifies those areas of the NECthat should be applied to MDCs and also includes additional new requirements where necessary.
New: 690.12 Rapid Shutdown of PV Systems on Buildings.
A new 690.12 entitled, "Rapid Shutdown of PV Systems on Buildings,” was added to the 2014 NEC. This section applies to solar photovoltaic (PV) systems installed on building roofs and would require that PV source circuits be de-energized from all sources within 10 seconds of when the utility supply is de-energized, or when the PV power source disconnecting means is opened. This will incorporate a significant improvement in safety for rooftop PV systems, based on the safety concerns of the first and second responders of the emergency and fire service communities during emergency operations on PV-equipped buildings and structures.
Photo 6. Provisions for rapid shutdown of PV systems on buildings was added to the 2014 NEC.
Chapter Seven – Special Conditions
New: Article 728 Fire-Resistive Cable Systems.
A new article has been added in the 2014 NECto address installations of fire-resistive cables. The installations of these cables are critical to their ability to function during a fire. These systems must be installed in accordance with very specific materials, supports, and requirements and are critical for the survivability of life safety circuits. There are diverse details for installing fire-rated cables that differ from other types of cables. Some of these variances pertain to conduit, conduit supports, and types of couplings, vertical supports, boxes, and splices. Without these details being included in the NEC, the installer and the enforcement community can be left uninformed.
New: Article 750 Energy Management Systems.
A new article was added to provide some general requirements that address the types of loads permitted to be controlled through energy management, which has become commonplace in today’s electrical infrastructure through the control of utilization equipment, energy storage, and power production. Installation codes currently establish requirements for utilization equipment, energy storage and power production that address facility and personnel safety. However, limited consideration has been given to installation codes which would serve to actively manage these systems. This would provide a means to reduce energy costs or to support peak power needs for a much broader electrical infrastructure demand. This article resulted from the work of the Smart Grid Task Group appointed by the Technical Correlating Committee. This task group identified two key areas of focus which included interconnection and energy management systems. The article includes such things as definitions, requirements for alternative-power sources, load-management provisions and field-marking requirements.
Chapter Eight – Communication Systems
Revision: 830.24 Mechanical Execution of Work.
A revision to this section will require nonmetallic cable ties and other nonmetallic cable accessories used to secure and support communication cables to be listed as having low smoke and heat release properties when used in plenums. This same change occurred at 770.24; 800.24; 820.24; and 830.24.
These are just a few of the changes that have been incorporated into the new 2014 NEC. When you get your new copy of the 2014 NEC, might I suggest that you take your old copy of the 2011 NEC and put a sign on it saying, "Free Code Book – Take It!” On second thought…never mind!
Read more by L. Keith Lofland
Posted By Mark C. Ode,
Monday, July 01, 2013
Updated: Thursday, June 20, 2013
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This article analyzes the new technology of low-voltage lighting and power distribution at 30 volts or less using the suspended ceiling grid as a lighting and power distribution system. Article 410 covering luminaires and Article 411 covering low-voltage lighting systems at 30 volts or less are two primary lighting installation articles in the National Electrical Code (NEC) pertaining to this new technology. A thorough understanding of the relationship of these two NEC articles with respect to ceiling grid low-voltage lighting and power distribution is one of the prime topics of this article. New Article 393, Low-Voltage Suspended Ceiling Power Distribution Systems, has been accepted for the 2014 NEC and expands the prior application of Articles 410 and 411, as applied to low-voltage lighting power distribution, to cover the new wiring method of low-voltage suspended ceiling power distribution. This new article expands the use of low-voltage power distribution system for non-lighting systems and identifies associated listed components for functions other than lighting, such as audio video equipment, HVAC actuators, air/temperature sensing devices, information technology equipment, as well as numerous other uses.
Information on various old and new products for lighting and other uses will be provided where these products are being adapted to work within the framework of the NEC for this new technology. Studying the acceptance of this technology for lighting, and then viewing the expansion of the supporting technology with the electrical industry’s rapid implementation of this new low-voltage power concept, coupled with other innovative applications, are key points underscoring the need for this new technology. To spread the understanding of this concept and to provide the user with a complete understanding of this technology, the first step is to provide a brief history of how this technology was developed, profiling the early attempts to have the ceiling grid power distribution technology specifically adopted into the NEC. The second step is to determine where the technology is at the present time inclusive of how the NEC covers low-voltage ceiling grid technology as an important part of the overall construction technology as it currently exists. The third step anticipates where the low-voltage ceiling grid technology is at the present time and will be in the future, covering both lighting and other uses.
Photo 1. Low-voltage suspended ceiling power distribution system
This new technology was derived by the realization of some people in the electrical industry that supplying permanent power for lights, receptacles, and other equipment in an office area within a building did not permit flexibility or ease of revision, remodeling, or reconstruction within these areas. A segment or coalition of the construction manufacturing community began work on a method of establishing an easier and less expensive method of providing power for general lighting and power loads and task lighting in an office area. The designers and developers of this new technology had to determine what the NEC would permit and then integrate the existing systems into a highly flexible wiring system. Decisions had to be made about the power source to be used, how to distribute power to the equipment, the type of connections to the power source that would be both safe and compliant with the NEC and the overall functional design of the system. In addition, determining the power level for any new system was a major concern since the higher the voltage and amperage for a power system, the less system flexibility.
The NEC provided the technical basis for using low-voltage power for the ceiling grid low-voltage power distribution in Article 725 and similar but related articles. For example, Article 640 covered audio signal processing, amplification, and reproduction equipment (audio and video equipment) and permitted Class 2 and Class 3 low-voltage power and wiring methods in accordance with Article 725. Heating and air-conditioning systems, designed with Classes 2 and 3 low-voltage power systems for heating and air-conditioning controls and thermostats, as well as control of variable air volume (VAV) dampers, rely upon Article 430 for motors, on Article 440 for air-conditioning systems, and on Article 422 for appliances. While Class 2 or 3 power-limited systems are often used for motor controls, as noted by requirements in430.72, Article 725 generally covers remote control, signaling, and power-limited circuits. Therefore, the low-voltage ceiling grid power distribution design coalition determined that Article 725 was the key to providing the power for this low-voltage lighting ceiling grid distribution system.
Photo 2. Installation of load connector to grid rail
Class 2 and Class 3 control, signaling, and power-limited circuits are low voltage with low-amperage circuits, or very low amperage with higher-rated voltage circuits that, due to their power limitations, will not normally initiate or start a fire since the energy source is low enough to not provide ignition of most material. Class 3 circuits can be a shock hazard due to their higher ampacity but are not normally a fire hazard; while Class 2 circuits will not provide ignition to most flammable materials and do not have enough energy to provide a shock hazard to personnel in a dry application, especially where the cables, components, and power supply are insulated by at least 150-volt insulation.
There are two different categories for Class 2 and Class 3 circuits with the technical characteristics of the two power-supply categories located in Tables 11(A) and 11(B) within Chapter 9 of the NEC. Table 11(A) covers alternating current (ac) power source limitations, and Table 11(B) covers direct current (dc) power source limitations. Both tables have inherently limited power supplies and not-inherently limited power sources as applied to both Class 2 and Class 3 power sources, with more to be explained on these two issues later. With an inherently limited power source, overcurrent protection is not required. With a not-inherently limited power source, overcurrent protection is required. As can be seen in Tables 11(A) and 11(B), Class 2 circuits have three basic voltage and amperage columns for inherently limited power supplies; and two basic voltage, amperage, and power columns for not-inherently limited power supplies. Class 3 circuits have one voltage, amperage, and power column for inherently limited power supplies, and two for not-inherently limited power sources. There is more emphasis on the Class 2 systems in this article, since Class 2 systems are used to supply power for the low-voltage ceiling grid power distribution systems.
Basics for NEC Coverage — General Requirements
Before covering the requirements for Class 2 and Class 3 remote-control, signaling and power-limited circuits found within Article 725, basic Code arrangement must first be understood. This basic requirement is covered in 90.3 of the NECthat states that the Code is divided into the introduction and nine chapters. The first four chapters cover general electrical requirements [Chapter 1: General electrical requirements; Chapter 2: Wiring and Protection; Chapter 3: Wiring Methods and Materials; and Chapter 4: Equipment for General Use]. Chapters 5, 6, and 7 are specialty chapters dealing with special occupancies, special equipment, or other similar types of special conditions, respectively, involving these special occupancies or equipment. Since these three specialty chapters cover special equipment and occupancies, the general rules and requirements found in the first four chapters can be supplemented or modified by the information found in Chapters 5, 6, and 7. This means that allof the general requirements in Chapters 1 through 4 must be followed unless special equipment, special occupancies, or special conditions require or permit us to deviate from the general rules. Specific requirements for low-voltage circuits covered in Article 725 can add to or amend any requirements for similar circuits found within Chapters 1 through 4. Section 90.3 also permits requirements that are located in Chapter 3 and in Article 725, specifically, to apply to the low-voltage suspended ceiling power distribution wiring system that will be located in new Article 393, covering the installation of low-voltage suspended ceiling power distribution systems as stated in the scope of this new article.
Photo 3. Grid Class 1 power server module
These specialized remote-control, signaling, and power-limited circuits are characterized and identified by usage and by any power limitations that are designed into the circuits. This usage and power limitation is what differentiates these specialized circuits from general power and lighting circuits. For this reason, Article 725 provides an alternative to the requirements for general lighting and power circuits that are covered by Chapters 1 through 4. There are different methods for determining wire sizes for these circuits, special derating factors, overcurrent protection for the circuits, insulation requirements for both the conductors and the equipment used in the circuits, and the wiring methods and materials that are used for the low-voltage circuits.
This concept has been further expanded in other sections of the Code, such that new Section 393.10 states, "Low-voltage suspended ceiling power distribution systems shall be permanently connected and shall be permitted … for listed utilization equipment capable of operation at a maximum of 30 volts ac (42.4 volts peak) or 60 volts dc (24.8 volts peak for dc interrupted at a rate of 10 Hz to 200 Hz) and limited to Class 2 power levels in Chapter 9, Table 11(A) and Table 11(B) for lighting, control, and signaling circuits.” In other words, this section states that these circuits must be limited to Class 2 power levels as detailed in Tables 11(A) and (B) in Chapter 9 and protected based on the table applications as indicated in the table notes. For example, some low-voltage equipment is protected by the inherent impedance of the power supply that precedes the control equipment in the circuit. If a Class 2 transformer has enough impedance in its secondary winding, the inherent impedance will protect the equipment and any conductors located on the secondary side of the transformer. The conductors that are used to supply power to the ceiling grid, and are connectedusing a transformer, are also protected by the impedance-limited transformer secondary. If too much current were to occur within the secondary of the transformer circuit, the windings in the transformer secondary willopen before damage to either the conductors or the components occur, thus providing the inherent protection of the circuit.
Photo 4. Grid bus rail
The primary of the transformer is still protected by some other means of overcurrent protection, such as fuses or circuit breakers. Section 393.45(A) provides overcurrent protection for the line side of the Class 2 power supply by stating that the listed Class 2 power supply or transformer primary must be protected at not greater than 20 amperes. Section 393.45(B) covers interconnection of power sources by stipulating that listed Class 2 sources must not have the output connections paralleled or otherwise interconnected, unless listed for such interconnection. This will ensure that the Class 2 limitations and protection requirements are maintained without fear of jeopardizing the safety of the circuit. In addition, 393.45(A) permits suspended ceiling low-voltage power distribution systems to have reverse polarity (backfeed) protection of dc circuits by either (1) if the power supply is provided as part of the system, the power supply is provided with reverse polarity (backfeed) protection; or (2) if the power supply is not provided as part of the system, reverse polarity or backfeed protection is provided as part of the grid rail busbar or as a part of the power feed connector.
New Article 393 incorporates quite a few new definitions that are unique to low-voltage suspended ceiling power distributions systems. For example, low-voltage suspended ceiling power distribution system "serves as a support for a finished ceiling surface and consists of a busbar and busbar support system to distribute power to utilization equipment supplied by a Class 2 power supply.” Busbar support is "an insulator that runs the length of a section of suspended ceiling bus rail that serves to support and isolate the busbars from the suspended grid rail”; whereas, a grid bus rail is "a combination of the busbar, busbar support, and the structural suspended ceiling grid system.” A general term for connectorwas provided as "an electromechanical fitting,” but a load connector is "an electromechanical connector used for power from the busbar to” whatever utilization equipment is connected to the busbar. A pendant connector is "an electromechanical or mechanical connector used to suspend low-voltage luminaire or utilization equipment below the grid rail and to supply power from the busbar to utilization equipment.” A power feed connector is "an electromechanical connector used to connect the power supply to a power distribution cable, to connect directly to the busbar, or from a power distribution cable to the busbar.” A rail-to-rail connector is "an electromechanical connector used to interconnect busbars from one ceiling grid rail to another grid rail.” A rail is "the structural support for the suspended ceiling system typically forming the ceiling grid supporting the ceiling tile and listed utilization equipment, such as sensors, actuators, A/V devices, and low-voltage luminaires and similar electrical equipment.” Finally,reversepolarity protection (backfeed protection) is a "system that prevents two interconnected power supplies, connected positive to negative, from passing current from one power source into a second power source.”
Based on 393.57, connections for busbar grid rails, cables, and conductors must be made with listed insulating devices, and these connections must be accessible after installation. Where connections are made in a wall or a concealed location, these connections must be installed in an enclosure in accordance with Parts I, II, and III of Article 314, as applicable. Induction of current into metal conduit or metal enclosures is covered in 300.20; and thesealing of penetrations into hollow spaces, vertical shafts, through walls, ceilings, partitions, and floors or into ventilation or air-handling ducts is still required by Section 300.21. Sections 300.22(B) and (C) detail the requirements for the installation of wiring in fabricated ducts or other spaces used for environmental air. Grounding of the supply side of a Class 2 power source is covered in 393.60(A) by requiring the supply side of the Class 2 power source to be connected to an equipment grounding conductor in accordance with the applicable requirements in Part IV of Article 250. However, the load side of the Class 2 power source does not permit the Class 2 load-side circuits for suspended ceiling low-voltage power grid distribution systems to be grounded at all. This ungrounded low-voltage system helps ensure safety similar to other low-voltage systems not grounded as indicated in 250.22.
The construction specifications for low-voltage suspended ceiling power distribution systems are provided in 393.104 covering sizes and types of conductors. On the load side, 393.104(A) states that current-carrying conductors for load-side utilization equipment shall be copper and shall be 18 AWG minimum. There is also an exception dealing with the size of conductors that states conductors of a size smaller than 18 AWG but not smaller than 24 AWG shall be permitted to be used for Class 2 circuits. Where used, these conductors shall be installed in a Chapter 3 wiring method, totally enclosed, shall not be subject to movement or strain, and shall comply with the ampacity requirements in Table 522.22. In 393.104(B), the power feed bus rail can be 16 AWG minimum or equivalent. For a busbar with a circular cross section, the diameter shall be at least 0.051 in. (1.29 mm) minimum; and for other than circular busbars, the area must be at least a 0.002 in.2 (1.32 mm2) minimum.
Low-Voltage Ceiling Grid Technology — Now and in the Future
This article has provided the technical information and background for suspended ceiling grid low-voltage lighting systems, as well as a glimpse into the future about the technical aspects of a low-voltage suspended ceiling grid power distribution system to supply countless other devices in many different aspects of daily living within an office environment. Some of this new technology is already available on the market; some is being developed as this article is being written, and new technology related to the suspended ceiling grid power distribution may yet be developed. The low-voltage grid system can supply low voltage to luminaires, in-wall audio video systems, office furniture, and under-floor as well as under-carpet distribution and equipment. Security systems and occupancy sensors can be powered by these distribution buses. Ceiling tile-type speakers have already been developed so music and other communication can be piggybacked onto the dc supply on the grid and then tapped to provide for easy surround sound for audio applications. With the advent of new solar photovoltaic technology, window panels with future technology solar photocell coatings could provide direct power to the suspended ceiling grids. Building management control systems for lighting, heating, cooling and all other aspects of building functions can be controlled using a suspended ceiling grid distribution connection to the building energy management system. Fire alarm hard-wired devices could be installed to a permanent source of dc supply with location and connection made just as conveniently and as easily accomplished as the installation of wireless fire alarm devices.
To address the advent of this new technology, UL has published ANSI/UL 2577 Standard for Safety for Suspended Ceiling Grid Low Voltage Systems and Equipment and certifies (Lists) this type of equipment under two product categories that cover the systems as well as the luminaires, connectors, power units and other accessories. These product categories are Suspended- Ceiling-Grid Low-Voltage Lighting Systems (IFFA) and Suspended-Ceiling-Grid Low-Voltage Lighting System Accessories (IFFC) located on page 192 and 193 respectively of the 2013 UL White Book. This is also available online at www.ul.com/database by entering IFFA or IFFC at the category code search field.
As technology changes, the construction and commercial office industry, as well as the various codes and standards affecting the construction of offices, have reacted to provide a safe and reliable method for the appropriate flexibility of power for lighting, sensors, temperature control, and other functional aspects of an office. The low-voltage grid distribution system is a very viable and important part of this flexible power distribution system.
1National Electrical Code (NEC) 2014 Edition
Read more by Mark C. Ode
Posted By Steve Douglas,
Monday, July 01, 2013
Updated: Thursday, June 20, 2013
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Code users would be interested in the safety
objective of the requirement for working space about electrical equipment and
the evolution of this requirement.
requirements for electrical equipment first appeared as two rules in the first
edition of the Canadian Electrical Code Part I (CE Code) dated 1927. Rule 2001
"(a) Adequate clear working space with secure footing shall be provided
about all electrical equipment which requires adjustment or examination during
operation or while danger of shock is present.” and Rule 7001 (f) "Passageways
around such machinery and equipment as generators, transformers and
switchboards shall be kept clear of any obstructions and so arranged as to give
authorized persons ready access to all parts requiring attention.” These
rules remained unchanged until the fourth edition of the CE Code dated 1939
where the words "during operation” were moved to the end of Rule 2001(a) "or
examination while danger of shock is present during operation or otherwise.” This change required the working space for
equipment only during adjustment or examination.
Photo 1. 5-kV indoor switchgear with two means of egress.
Between 1939 and 1969 these rules were moved four
times resulting in Rule 2001(a) as Rule 2-072, and Rule 7001 as Rule 2-076.
During the rule relocation in the 1969 CE Code both rules were reworded.
Photo 2. 27.6-kV outdoor switchgear with one means of egress.
Photo 3. Low voltage electrical room with one means of egress, and a 600-V 800-Amp main distribution switchboard and a 225-kVA transformer.
2-072 Working Space about Electrical Equipment (Low Potential)
working space of three feet with secure footing shall be provided and
maintained about all electrical equipment which may require adjustment and
maintenance while danger of electric shock is present, except that working
space is not required behind assemblies such as dead-front switchboards or
motor control centres where there are no renewable parts such as fuses or
switches on the back and where all connections are accessible from locations
other than the back.” This rule
rewording had three significant changes, one was the excepting not requiring
working space behind dead-front switchboards and motor control centres where
there are no renewable parts such as fuses or switches on the back and where
all connections are accessible from locations other than the back. Second was
that the working space was required to be maintained, not just during
adjustment or examination. Third was the introduction of a measurement of 3
feet. The intent of the 3 feet of working space with secure footing is to
provide adequate space for maintenance of the electrical equipment.
2-076 Accessibility for Maintenance
working space around electrical equipment shall not be used for storage and
shall be kept clear of obstructions and so arranged as to give authorized
persons ready access to all parts requiring attention.” The main
change here is the removal of "such machinery and equipment as generators,
transformers and switchboards” requiring passageways and working space for
all electrical equipment.
In addition to the changes to these two rules, a new
rule [Rule 2-074] was added regarding a requirement for entrances to working
2-074 Entrance to Working Space
"(1) At least one
entrance of sufficient area shall be provided to give access to the working
space about electrical equipment.
(2) Doors or gates of suitable material may be
provided but they shall be capable of being readily opened from the equipment
side without the use of a key or tool.”
In the eleventh edition dated 1972, Rule numbers
2-072 and 2-074 were changed to 2-308 and 2-310. Subrule (2) was also added to
Rule 2-308: "(2) The minimum head room of working space about switchboards
or motor control centres where bare parts are exposed at any time shall be 7
In the next
edition, dated 1975, the title of Rule 2-308 was changed to: 2-308 Working
Space About Electrical Equipment (Low Voltage), and Subrule (2) of Rule 2-310
was renumbered to Subrule (4), and Subrule (1) was replaced with Subrules (1),
(2), and (3):
2-310 Entrance To, and Exit From, Working Space
"(1) Each room
containing electrical equipment and each working space about equipment shall
have suitable means of exit and entrance, which shall be kept clear of all
(2) An exit may also be used as an entrance.
(3) If the plan of the room or space and the
characteristics and arrangement of equipment are such that an accident would be
liable to close or make inaccessible a single exit, a second exit shall be
(4) Doors or gates shall be capable of being
readily opened from the equipment side without the use of a key or tool.”
Subrule (3) was the first requirement in the CE Code
for a second exit from an electrical room.
The only change in the thirteenth edition, dated
1978, was to change the imperial measurements to metric.
In the fourteenth
edition, dated 1982, the title of Rule 2-308 was changed removing the reference
to low voltage, Subrule (2) of Rule 2-308 was renumbered as Subrule (4), and
Subrule (1) was reworded adding "such as switchboards, panelboards, control
panels, and motor control centres that are enclosed in metal,” to the
working space requirements. It is interesting to note that transformers and
other equipment that are not required functions of adjustment, control or
operation have not been included in the list of equipment requiring the working
space. In addition new Subrules (2) and (3) were added with consideration for
drawout-type equipment, the need to open enclosure doors to at least 90⁰, and
introduction of Table 56 detailing the minimum working space around electrical
equipment having exposed live parts.
Drawing 1 showing an unacceptable egress path width of 0.6 m
Drawing 2 showing an acceptable egress path width of 0.75 m.
Drawing 3: With equipment rated less than 1200 Amp and less than 750 V the transformer is not considered when determining the working space, but the egress path must not be less than 0.75 M.
Drawing 4: With two exit doors located so as to allow exit from the working space without passing any possible failure point in the equipment, the minimum depth of working space is 1.0 m.
Drawing 5: With only one exit door not located so as to allow exit from the working space without passing any possible failure point in the equipment, the minimum depth of working space is 1.5 m.
2-308 Working Space Around Electrical Equipment
"(1) A minimum
working space of 1 m with secure footing shall be provided and maintained about
electrical equipment such as switchboards, panelboards, control panels, and
motor control centres that are enclosed in metal, except that working space is
not required behind such equipment where there are no renewable parts such as
fuses or switches on the back and where all connections are accessible from
locations other than the back.
(2) The space
referred to in Subrule (1) shall be in addition to the space required for the
operation of drawout-type equipment and shall be sufficient for the opening of
enclosure doors and hinged panels to at least 90°.
(3) Working space with secure footing not less
than that specified in Table 56 shall be provided and maintained around
electrical equipment such as switchboards, control panels, and motor control
centres having exposed live parts.
(4) The minimum headroom of working spaces around
switchboards control panels and motor control centres where bare live parts are
exposed at any time shall be 2.2 m.”
In the sixteenth edition of the CE Code, dated 1990,
Subrule (2) of Rule 2-308 was reworded adding more details for drawout-type equipment
in either the connected, test, or fully disconnected position.
"(2) The space
referred to in Subrule (1) shall be in addition to the space required for the
operation of drawout-type equipment in either the connected, test, or fully
disconnected position and shall be sufficient for the opening of enclosure
doors and hinged panels to at least 90°.”
Subrules (2) and (3) of Rule 2-310 were replaced in
the eighteenth edition, dated 1998, with more specific requirements detailing
when the working space referred to in Rule 2-308 needs to be increased to 1.5
"(2) Where a room or space referred to in Subrule
(1) contains equipment that has a rating on the equipment that is rated 1200 A
or more, or rated over 750 V, and consists of transformers, overcurrent
devices, switchgear, or disconnecting means, such equipment shall be arranged
so that, in the event of a failure in the equipment, it shall be possible to
leave the room or space referred to in Subrule (1) without passing the failure
point, except that where this cannot be done, the working space requirement of
Rule 2-308(1) and (2) shall be not less than 1.5 m.
(3) For the purposes of Subrule (2), the potential
failure point is any point within or on the equipment.” These new subrules
require the room or space be such that it is possible to leave the room or
space without passing any part of equipment rated 1200 A or more, or rated over
750 V. Where it is not possible to leave the room or space without passing any
part of the equipment, the working space must then be increased to 1.5 m.
Another significant change to note is that Subrule (2) includes transformers
indicating that when a room or space with equipment rated 1200 A or more, or
equipment rated over 750 V includes a transformer the working space about the
transformer must also be considered.
These rules remained unchanged until the twentieth edition
dated 2009 were Subrule (1) of Rule 2-310 was changed to read: (1) Each room
containing electrical equipment and each working space around equipment shall
have unobstructed means of egress in compliance with the National Building Code
of Canada. In addition to this subrule change, the following note was added
to Appendix B: Specific requirements pertaining to unobstructed means of
egress can be found in Articles 188.8.131.52 and 184.108.40.206 of the National Building
Code of Canada. Both Articles 220.127.116.11 and 18.104.22.168 of the National
Building Code of Canada restrict the width of a normal means of egress from
any part of a floor area to less than 750 mm. As an example, Drawing 1 shows an
electrical room with egress path from the working space about the 1200 Amp
panel limited to 0.6 m. This example does not meet the requirements in the
building code for an egress path with a minimum width of 0.75 m.
Subrule (2) for Rule 2-310 was revised again in the
twenty-second edition of the 2012 CE Code, and added wording regarding the
rating on the nameplate.
"(2) Where a room or space referred to in Subrule
(1) contains equipment that has a rating on the equipment nameplate of 1200 A
or more, or is rated over 750 V, and consists ... This change was a result
of an interpretation request asking if this rule applied to equipment that has
a maximum name plate rating of 1200 A and a main overcurrent device that is
less than 1200 A. The answer shown in the 2009 CE Code is yes. The change to
Subrule (2) was to clarify the intent of the subrule is to apply based on the
nameplate rating of the equipment.
Drawing 6: With two exit doors located so as to allow exit from the working space without passing any possible failure point in the equipment, the minimum depth of working space is 1.0 m.
Drawing 7: With only one exit door not located so as to allow exit from the working space without passing any possible failure point in the equipment, the minimum depth of working space is 1.5 m.
Drawing 8: With two exit doors located so as to allow exit from the working space without passing any possible failure point in the equipment. The minimum depth of working space is 1.0 m with the drawout-type equipment fully drawn out and with sufficient for the opening of enclosure doors and hinged panels to at least 90°.
Drawing 9: With no renewable parts such as fuses or switches on the back and where all connections are accessible from locations other than the back, the space between the wall and the panel is not required to be 1M.
Drawing 10: With equipment rated 1200 Amp or greater or with high voltage equipment, the transformer must be considered when determining the working space.
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Posted By Steve Douglas,
Wednesday, May 01, 2013
Updated: Tuesday, April 30, 2013
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Residential load calculations first appeared in the Canadian Electrical Code Part I (CE Code) in the second edition dated 1930. In the 1930 edition, the load calculation rules were in Section 6 Conductors. The calculations were quite different from the present day calculations. For residential installations, the calculations were based on the number of branch circuits being installed instead of the dwelling floor area. In the fourth edition, dated 1939, a demand factor table for lighting load based on the floor area was added. In the sixth edition dated 1953, the Conductor Section including the load calculation requirements were moved to Section 4 Conductors. This calculation format remained until the seventh edition, dated 1958. A new section called Circuit Loading and Demand Factors including the single dwelling load calculations was added as Section 8 to the eighth edition of the CE Code dated 1962.
Photo 1. Single dwelling units as defined in the CE Code Part I
In the 1958 edition, calculations were similar to the calculations of today with the main difference in the calculations being the basic load. The basic load covering lighting and convenience outlets was 3,500 W for a residence with a living area up to 500 ft² (46.5 m²). For a residence with a living area over 500 ft² and up to 1500 ft² (139.4 m²), the basic load was 4,500 W with an additional 1000 W for each 1000 ft² (93m²) or portion thereof. The 1958 basic load requirements stayed the same until the twelfth edition dated 1975 when the basic load was increased to the requirements of the current code.
Rule 8-200 of the 2012 CE Code covers load calculations used to determine the minimum feeder or service size for single dwelling units. To start off, we should establish what a dwelling unit is. Section 0 defines a single dwelling unit as "a dwelling unit consisting of a detached house, one unit of row housing, or one unit of a semi-detached, duplex, triplex, or quadruplex house,” and a dwelling unitas "one or more rooms for the use of one or more persons as a housekeeping unit with cooking, eating, living, and sleeping facilities.” Subrule (1) of Rule 8-200 is divided into two items (a) and (b). Item (a) details the specific criteria for calculations and Item (b) mandates the absolute minimum allowable ampacity of the service or feeder size – based on the floor area. 100 A is required by the Code where the floor area of the single dwelling, exclusive of basement floor area, is 80 m² (861 ft²) or more, and 60 A is the minimum permitted service/feeder ampacity – where the floor area of the single dwelling, exclusive of basement floor area, is less than 80 m². Item (a) is further divided into seven items (i) to (vii).
Items (i) and (ii) detail a basic load for the dwelling unit. This basic load includes 120 V 15- and 20-amp convenience outlets, lighting loads and motor loads rated up to 1500 W. The basic load for the dwelling unit is 5000 W for the first 90 m² (968 ft²) of living area plus an additional 1000 W for each 90 m² or portion thereof in excess of 90 m². The living area is determined as 100% of the ground floor, 100% of any area used for living purposes on the upper floor, plus 75% of the basement area of the dwelling unit.
The next step in Item (iii) is to add the electric space-heating and air-conditioning loads. Where it is known that the installed electric space-heating and air-conditioning loads will not be used simultaneously, the larger of the electric space-heating load or the air-conditioning load is added to the base load. For electric space-heating systems consisting of electric thermal storage heating, duct heater, or an electric furnace, the connected heating load is calculated at 100% of the equipment ratings. Where the electric heating installation is provided with automatic thermostatic control devices in each room or heated area, the electric space-heating load is 100% of the first 10 kW of connected heating load plus the balance of the connected heating load at a demand factor of 75%.
Photo 2. A 11 kW electric range used in the article example
The next loads to add are any electric ranges.Item (iv) allows 6000 W for a single range to be added to the basic load provided the range does not have a rating in excess of 12 kW. In the event the electric range is rated more than 12kW, 40% of any amount exceeding 12 kW will need to be added as well.
Now we add water heaters. Item (v) indicates any electric tankless water heaters or electric water heaters for steamers, swimming pools, hot tubs, or spas are added to the basic load at 100% of equipment ratings.
Item (vi) is new for the 2012 CE Code and requires that any electric vehicle charging equipment loads also be added to the basic load at 100% of equipment ratings.
The final step in Item (vii) is to add any additional loads at 25% of the rating of each load with a rating in excess of 1500 W if an electric range has been provided for, or 100% of the rating of each load with a rating in excess of 1500 W up to a total of 6000 W plus 25% of the load in excess of 6000 W if an electric range has not been provided for.
Photo 3. The nameplate of a 1500 W microwave oven
Photo 4. A 1500 W microwave oven used in the article example
As an example we will look at a 269 m² (2900 square foot) residence with the following loads:
- lighting load
- 4 small appliance branch circuits
- laundry circuit 1500 W
- natural gas heating
- air conditioner 6000 VA
- electric range 11,000 W
- hot tub 8000 W (2 hp motor)
- Level II electric vehicle charger 7200 W
- electric dryer 5000 W
- garbage disposal 800 W
- microwave 1500 W
- dishwasher 1200 W
- electric water heater 4500 W
The calculated load for the 2900 ft² (269 m²) single dwelling in this example is 173.1 amps.
The basic load is calculated based on the floor area of the single dwelling. The load for the first 90 m² is 5000 W, leaving 179 m² of floor area. The next 90 m² has a load of 1000 W, and an additional 1000 W for the remaining 89 m². The total basic load of 7000 W includes the lighting, convenience receptacles, small appliance branch circuits, laundry circuit, garbage disposal, and the dishwasher.
The heating of the single dwelling is a gas furnace and no electric heat is installed, leaving the 6000 W air-conditioning load added with a demand factor of 100%.
The electric range for this single dwelling is less than 12 kW providing a load for the calculation of 6000 W.
The 8000 W hot tub and the 7200 W electric vehicle charging equipment are now added with a demand factor of 100%.
Any additional loads with a rating in excess of 1500 W are now added with a demand factor of 25%. In this example, the additional loads over 1500 W are the 5000 W dryer and the 4500 W storage type water heater; 25% of the 9500 W gives us 2375 W to be added to the calculation.
Table 1. Summary of the single dwelling service load calculation
Now that we know the calculated load, we can determine the minimum service and conductor size. The ampacity of the load is 173.1 amps (41550 / 240 = 173.1). In most installations, the continuous load on a service is limited to the continuous load rating of the equipment being used. Subrule (3) of Rule 8-104 considers all loads continuous unless it can be shown that in normal operation the load will not persist for a total of more than one hour in any two-hour period for loads not exceeding 225 amp, or a total of more than three hours in any six-hour period for loads in excess of 225 amp. In the case of single dwelling units Subrule (2) of Rule 8-200 allows these loads to be considered as a non-continuous load for application of Rule 8-104. However, although Section 86 considers the EV charging equipment to be a continuous load, when this load is calculated for the purpose of defining the ampacity of a service in a single dwelling, such EV charging equipment load is not considered as continuous load, similarly to all other loads under this Rule. This means 100% of the calculated load for a single dwelling can be used to determine the service equipment ampere rating. For our 269 m² example a standard rating of 175 amp overcurrent device could be selected in the service box as the calculated load is 173.1 amp. Typically 175 amp rating of the overcurrent device will necessitate installation of the 200 A rated service box, as 175 A rating for the service fused disconnect or the service circuit breaker for residential installations is not available. In most cases a 200-amp service would be installed with a 175-A or 200-A trip setting or rating. Let’s consider that the trip setting of the service overcurrent device was selected at 200 A.
The size of the service conductors are now established using Rules 4-004, 4-006, and 14-104. As all distribution equipment presently available has a temperature limitation of 75⁰C, Rule 4-006 requires the allowable ampacity to be based on the 75⁰C column of either Table 2 or 4 for conductors installed in a raceway. The smallest 75⁰C conductor allowable ampacity from Tables 2 and 4 for the calculated load of 173.1 amp are 2/0 copper with an allowable ampacity of 175 amp, or 4/0 aluminum with an allowable ampacity of 180 amp.
Photo 5. The nameplate for a 1200 W dishwasher used in the article example
The next step is to verify the conductor selected meets the requirements of Rule 14-104. Rule 14-104 requires the overcurrent device to have a setting not higher than the allowable ampacity of the conductors being protected. Where the conductor allowable ampacity does not correspond with the overcurrent protection commercially available, Table 13 provides details on acceptable limits for over protection settings. Based on the fact that a 200-amp service will be installed with a main 200-amp trip setting for the breaker, Table 13 limits the conductor allowable ampacity to be not less than 176 amps. In the case of the copper conductors, the 2/0 copper conductor with the allowable ampacity of 175 amp is undersized. At this point some code users will try to apply "the 5% rule” in Subrule (1) of Rule 8-106 to the 175 allowable ampacity of Table 2. Subrule (1) of Rule 8-106 allows loads calculated in accordance with Section 8 to be within 5% of the allowable ampacity of the conductors selected. This means the 5% allowance can be applied to a calculated load. Applying the "5% rule to a conductor allowable ampacity table is a misapplication of Subrule (1).
In summary, the minimum conductor size allowed for the 200-amp service where the conductors are installed in a raceway for the example in this article is either 3/0 copper or 4/0 aluminum. If the main breaker of this service was reduced to 175 amp the minimum copper conductor size could be reduced either 2/0, and the aluminum conductor would remain at 4/0.
Read more by Steve Douglas
Posted By Steve Foran,
Wednesday, May 01, 2013
Updated: Tuesday, April 30, 2013
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In the early 90s, utilities were in the midst of massive change as downsizing, right-sizing—or whatever you called it — swept the continent. Driven by technology, fewer people were needed to get the same work done and from this emerged an industry called Process Re-engineering.
Our utility was engulfed in change. Our new business processes resulted in many changes in responsibilities for many people, but one affected our department very significantly. At the time we were responsible for technical training associated with revenue metering.
The proposed change would reduce both travel and the number of people needed to deliver metering services to residential customers by combining two separate job functions together into a single job. I cannot recall the exact numbers, but for illustrative purposes it was projected that we could combine the work of 15 meter installers and 95 meter readers into, say, 100 multi-disciplined metering workers, resulting in a net reduction of 10 people.
The challenge was that the technical competence required in the newly created position was higher than that of the 95 meter readers.
To safely perform their duties, meter installers must understand the meter nameplate, know how to identify the proper device for a service and be competent to work around energized equipment. Quite simply, the meter readers were not competent to do this work.
A comprehensive training program was developed and delivered. It covered many aspects of the residential service which included both theoretical and practical components where employees had to demonstrate their competency.
From the training, participants learned about the risks associated with metering and energized equipment. Most importantly, they obtained the knowledge and skills needed to safely manage the risks.
Of the many risks at the electrical service entrance, there is one that stands out above all others. This risk came as a surprise to every single participant in our training. In fact, none of the meter readers were aware that this risk even existed.
Most meter readers thought the greatest risk was electrical shock. Contact with 120 V is a risk; however, a far greater risk is the fault level available at the service entrance in the event of a ground fault. The potential physical harm to people and property as a result of a short circuit in a meter base can be catastrophic.
For our system, we calculated the maximum possible fault level at a 200 A 120/240 Volt service (close to a large substation, short service run, large distribution transformer, etc.). Here’s what we found: the power delivered in the event of a short circuit (even though only momentarily) is comparable to the power delivered by a typical jet engine that you see on the wings of a large airplane.
In our training, we explained this to our participants and asked them, "Would you stick a screw driver into a jet engine while it’s running? What kind of precautions would you take around a jet engine?”
A fault at a meter base has the ability to instantaneously produce the same power delivered by a jet engine. But unlike the jet engine, which makes all kinds of noise and produces so much wind that you wouldn’t dare get too close, a meter base just sits there — you can’t even tell if it is energized by looking at it.
Trainees told us that their biggest take-away was their newfound appreciation of something which they were previously unaware.
As for me, I learned that we must be open to looking at situations in new ways so we can see what was once invisible. Secondly, use appreciation (appreciation of the risk, work methods, design, etc.) to replace feelings of fear and lack of understanding.
The new service model was safely implemented and I hear from colleagues who still work at the utility that they continue to re-engineer their metering and customer services processes.
Read more by Steve Foran
Posted By Christel Hunter,
Wednesday, May 01, 2013
Updated: Tuesday, April 30, 2013
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Load calculations in the National Electrical Code have evolved over many decades. It was in the 1933 NEC that load calculation requirements began to resemble a format that the modern code user would find familiar. Since then, many things have changed, but the primary requirement remains the same — service equipment and conductors must be sized to handle the expected load.
Article 220 of theNational Electrical Code lays out the primary requirements for performing load calculations that are necessary for determining the size of a residential service. The calculations are based on the expected loads present in a dwelling unit, along with appropriate demand factors that are used to account for the diversity of electrical use by occupants. There are two methods available, standard and optional calculations. Optional calculations require fewer steps and generally result in smaller conductors, but the dwelling unit must meet more restrictive requirements. We will only be considering one-family dwelling units in this article, including single family residences, apartments, etc.
Be aware that some authorities having jurisdiction adopt the International Residential Code for One- and Two-Family Dwellings (IRC) and use the method for calculating the service size using the requirements found in Chapter 36. The IRC calculations are based on the National Electrical Code, but are not identical. Always check with your local jurisdiction to find out what method(s) are acceptable.
Photo 1. Electric range
The standard method for calculating service sizing is found in Part III of Article 220. Of course, we can’t find all the requirements in this Part, so we will also be looking at additional requirements in Articles 210, 220, 230, 250 and 310. An example load calculation using the standard method is shown in Table 1.
The first thing we need to determine is the lighting load. Table 220.12 requires that for dwelling units, we multiply the floor area (based on the outside dimensions of the dwelling unit) times 3 volt-amperes/square foot. Section 220.14(J) states that the following loads are also included in the general lighting load calculations:
- all general-use receptacle of 20-ampere rating or less, including the receptacles connected to the bathroom branch circuit required in 210.11(C)(3),
- the outdoor outlets in 210.52(E),
- the receptacle outlets in basements, garages, and accessory buildings in 210.52(G), and
- the lighting outlets required in 210.70(A), which includes habitable rooms, a variety of additional locations, and storage or equipment spaces.
Table 220.42 gives us demand factors for lighting loads. Most homes will take the first 3000 VA at 100% and the remainder at 35%. (If you are calculating a multifamily dwelling service, you might use the third demand factor category, where anything over 120,000 VA is taken at 25%.)
Small Appliance and Laundry Loads
Section 210.11(C)(1) requires a minimum of two small appliance branch circuits. Section 220.52(A) tells us that we must use a minimum load of 1500 VA for each of these circuits, but also allows the small appliance branch circuits to be included with the general lighting load when applying the demand factors in Table 220.12. Section 220.52(B) requires that 1500 VA be added for the required laundry circuit in 210.11(C)(2). This circuit can also be added to the general lighting load and demand factors may be applied.
Photo 2. Washer/dryer
Electric Dryers and Cooking Appliances
Section 220.14(B) refers us to requirements for electric dryers in 220.54 and electric cooking appliances in 220.55. Electric clothes dryers are calculated at either the minimum of 5000 watts or the nameplate rating, whichever is larger. The demand factors in Table 220.54 may be helpful if there are more than four dryers, but this is unlikely in a one-family dwelling unit, so we will not use this table for the examples in this article. Electric ranges and other electric cooking appliances (rated in excess of 1.75 kW) shall be permitted to be calculated in accordance with Table 220.55, which takes up an entire page and has five notes. There are also informational notes directing the code user to Annex D for examples. It is worthwhile to review this table and read all the notes and examples to become familiar with the various options.
If there are four or more fixed appliances in the residence, 220.53 permits all of these loads to be totaled and then a demand factor of 75% applied. Fixed-appliance loads include items such as a water heater, garbage disposal, dishwasher, microwave, etc.
Photo 3. Garbage disposal
Largest motor load
Section 220.14(C) tells us that motor loads shall be calculated in accordance with the requirements in 430.22, 430.24 and 440.6. For the service calculation, this means that we must determine the largest motor load and add 25% of its value to the total calculation. Common motor loads in residential applications include air conditioning, water pumps, disposals, blowers, etc. Often, the largest motor load in a home is the air conditioner. Even if the air conditioning is dropped from the total load calculation in favor of electric heating (see below), you may still be required to use the AC motor load for this calculation. Check with your jurisdiction to see what the policy is locally. Many jurisdictions publish residential load calculation worksheets to help with determining the size of the service.
When two loads are not likely to be energized at the same time, 220.60 allows us to use only the largest load for the calculation of the service. This is typically applied to dwelling units with both electric heating and air conditioning, since they are not expected to run at the same time.
Specific appliances or loads
There are certain loads that may be found in residences that are not included in the previous list. Section 220.14(A) requires that an outlet for a specific load or appliance not covered elsewhere must be calculated based on the ampere rating of the load served. Some examples might include a spa, RV hookup, etc. These must be included in the load calculation at their full value.
The optional method is much simpler than the standard calculation, but is restricted in 220.82 to "... a dwelling unit having the total connected load served by a single 120/240-volt or 208Y/120-volt set of 3-wire service or feeder conductors with an ampacity of 100 or greater.” Most one-family dwelling units meet this requirement, so the optional method is used frequently. An example calculation using the optional method is shown in Table 2.
For the purposes of the optional method, everything except heating and air conditioning is considered to be a general load. For this method, the general calculated load shall be not less than 100 percent of the first 10 kVA plus 40 percent of the remainder of all loads other than heating and air conditioning.
Lighting and general-use receptacles are again based on the outside dimensions of the dwelling unit multiplied by 3 volt-amperes/square foot. The small-appliance branch circuits and laundry branch circuit are each included at 1500 VA.
The next step is to determine the nameplate rating of each of the following items:
- all appliances fastened in place, permanently connected, or located to be on a specific circuit
- ranges, wall-mounted ovens, counter-mounted cooking units
- clothes dryers that are not connected to the laundry branch circuit
- water heaters
For all permanently connected motors not included in the previous list, the nameplate or kVA rating must be included in the calculation.
Heating and Air Conditioning
The largest heating and air-conditioning load must be chosen from six options:
- 100 percent of the nameplate rating of the air conditioning and cooling
- 100 percent of the nameplate rating of the heat pump when it is used with no supplemental electric heating
- 100 percent of the nameplate rating of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space-heating systems (If the heat pump compressor is prevented from operating at the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load.)
- 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units
- 40 percent of the nameplate ratings of electric space heating if four or more separately controlled units
- 100 percent of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value.
Comparing Standard and Optional Calculations
To see how the two methods compare, let’s take a look at a 2900 square foot residence with the following loads:
- lighting load
- 4 small appliance branch circuits
- laundry circuit 1500 W
- natural gas heating
- air conditioner 6000 VA
- electric range 11,000 W
- hot tub 8000 W (2 hp motor)
- Level II electric vehicle charger 7200 W
- electric dryer 5000 W
- garbage disposal 800 W
- microwave 1500 W
- dishwasher 1200 W
- electric water heater 4500 W
The standard calculation method is shown in Table 1 and the optional calculation method is shown in Table 2. Using the standard calculation, our total load is 47,520 VA. Dividing that by 240 volts gives us 198 amps. Using the next standard service rating requires that we use a 200-amp service. Since we have a 120/240-volt single-phase dwelling service, we are allowed to use NEC Table 310.15(B)(7) and use either 2/0 AWG copper or 4/0 AWG aluminum service conductors.
Using the optional calculation, our total calculated load is 34,160 VA. Dividing that by 240 volts gives us 142 amps. Using the next standard service rating requires that we use a 150-amp service. Once again, we are allowed to use NEC Table 310.15(B)(7), which requires either 1 AWG copper or 2/0 AWG aluminum conductors.
For this example, it is clear that the optional calculation permits a smaller service. From a practical perspective, due to equipment availability, it is likely that a 200-amp service will be installed rather than a 150-amp service.
Neutrals are permitted to be smaller than the phase conductors in most residential service installations. Section 220.61 requires that the neutral load be determined by calculating the maximum unbalanced load between the neutral and any one ungrounded conductor. The values used for calculating the neutral size when using the standard or optional methods will often be different, as shown in Tables 3 and 4.
Section 230.42 states that the grounded conductor for a service shall not be smaller than the minimum size as determined in accordance with 250.24(C). If we have a single raceway (as is most common for service conductors), 250.24(C)(1) tells us that the conductor cannot be smaller than specified in NEC Table 250.66, but is not required to be larger than the ungrounded conductors.
For our standard service calculation, our minimum ungrounded conductor size was a 2/0 AWG copper or a 4/0 AWG aluminum. Using NEC Table 250.66 would require a neutral no smaller than a 4 AWG copper or a 2 AWG aluminum. In Table 3, we found that our calculated neutral load is 28,035 VA. Dividing that by 240 volts gives us 117 amps, which will require either a 2 AWG copper or 1/0 AWG aluminum from Table 310.15(B)(7). These sizes are larger than the required minimum, so we choose one of these conductors.
For our optional service calculation, our minimum ungrounded conductor size was a 1 AWG kcmil copper or 2/0 AWG aluminum. Using NECTable 250.66 would require a neutral no smaller than 6 AWG copper or a 4 AWG aluminum. In Table 4, we found that our calculated neutral load is 30,320 VA. Dividing that by 240 volts gives us 126 amps, which will require either a 1 AWG copper or 2/0 AWG aluminum from NEC Table 310.15(B)(7). Since these sizes are larger than the required minimum, we would choose one of these conductor sizes.
Note that for this example in our optional method calculation, the neutral conductor is the same size as our phase conductors. However, if a 200-amp service is installed based on the standard calculation, the neutral is significantly smaller due to the calculation method. Table 5 shows a summary of the ungrounded and neutral conductor sizes for our example using both the standard and optional calculation methods.
To accurately calculate the service size for residential installations, the designer and installer must be familiar with many requirements in the National Electrical Code. The requirements are not necessarily straightforward, and it is recommended that additional resources be reviewed. Available resources include the examples in Informative Annex D of the NEC, the IAEI publication One- & Two-Family Dwelling Electrical Systems, and other published examples.
310.15(B)(7) – Changes for the 2014 NEC
residential services, the service conductors and main power feeders are allowed
to be sized based on Table 310.15(B)(7) instead of Table 310.15(B)(16), which
permits a smaller size conductor to be used in many cases. This allowance has
been in the NEC since the 1950s in recognition of the fact that only a
small portion of the electrical loads in homes are typically used at the same
time, so the load on the service conductors at any one time is generally much
smaller than the total calculated load.
The language in
Section 310.15(B)(7) and the associated table have been a subject of great
debate in code-making panel 6 (CMP-6) over the last few cycles. CMP-6 has
considered each of the proposals and comments received over the last few years
and come up with new wording to address the concerns and suggestions submitted.
CMP-6 has agreed to
delete the existing wording and table and replace them with the following
For one-family dwellings and the individual dwelling units of two-family
and multifamily dwellings, service and feeder conductors supplied by a single
phase, 120/240-volt system shall be permitted be sized in accordance with
310.15(B)(7)(a) through (d).
(a) For a service rated 100 through 400 amperes, the service conductors
supplying the entire load associated with a one-family dwelling or the service
conductors supplying the entire load associated with an individual dwelling
unit in a two-family or multifamily dwelling shall be permitted to have an
ampacity not less than 83% of the service rating.
(b) For a feeder rated 100 through 400 amperes, the feeder conductors
supplying the entire load associated with a one-family dwelling or the feeder
conductors supplying the entire load associated with an individual dwelling
unit in a two-family or multifamily dwelling shall be permitted to have an
ampacity not less than 83% of the feeder rating.
(c) In no case shall a feeder for an individual dwelling unit be required
to have an ampacity greater than that of its 310.15(B)(7)(a) or (b) conductors.
(d) Grounded conductors shall be permitted to be sized smaller than the
ungrounded conductors provided the requirements of 220.61 and 230.42 for
service conductors or the requirements of 215.2 and 220.61 for feeder
conductors are met.
Note No. 1: It is possible that the conductor ampacity will require other
correction or adjustment factors applicable to the conductor installation.
Informational Note No. 2: See example DXXX in Annex D.
In effect, the same
size conductors that are allowed in the 2011 NEC will still be allowed
in the 2014 NEC, assuming that temperature correction factors or
adjustment factors are not required for the installation. The changes to the
code language were necessary to take into account certain limitations inherent
in the language in previous code cycles. Because Table 310.15(B)(7) is based on
service or feeder ratings and not the temperature rating of conductors, there
is no clear way to apply adjustment or correction factors for installations at
higher temperatures or if there are more than three current-carrying conductors
in a conduit.
It should be noted that
the conductor sizing will still be based on the service or feeder rating, not
the calculated load. For example, if you have a calculated load of 184 amps and
are required to install a 200-amp service, the conductors would be required to
have an ampacity of 166 amps or more:
200 amps times 83 percent equals 166 amps. So, for a 200-amp service,
you would still be allowed to choose a 4/0 AWG aluminum or 2/0 AWG copper, but
you would choose it from the 75 degree C column in Table 310.15(B)(16).
Read more by Christel Hunter
Posted By Randy Hunter,
Friday, March 01, 2013
Updated: Wednesday, February 13, 2013
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In Part One of Article 240, we left off with a basic review of circuit protection. Now that we have an understanding of how it operates, let’s get back to Part II of Article 240 which starts at 240.21 Location in Circuit. Here we find a very simple statement which requires the overcurrent protection to be located at the point where ungrounded conductors receive their supply. As simple as this is, we naturally have exceptions which will allow taps to be made under certain conditions. For this section, a tap is a conductor which is connected to a system; however, it is not sized to handle the ampacity of the upstream overcurrent protective device. We will cover the limited allowable conditions. But first, the last sentence of 240.21 needs to be emphasized; it explains that under the tap allowances in 240.21(A) through (H), you may not have an additional tap made to any of these allowed taps, or as I used to tell inspectors, "You can’t tap a tap.”
Feeder Taps Rules
In 240.21(A) Branch-Circuit Conductors, we find a method of performing taps for branch circuits, but note that you are referred back to Article 210.19 and 210.20 for the exact applications. In subsection (B) we start to deal with the Feeder Taps, which are further broken down to five conditions. I’m not going into details on each of these sections, just a brief overview of the different rules; so again, I will challenge you to open your code book and review the specific conditions for each of these allowances. First, we have a tap rule not over 10 feet in length. Please note that when we have a length in this section it is the actual length of the conductor from connection point to connection point. The 10-foot rule has four conditions which must be met. Note that if these conductors leave the enclosure from which they are tapped, the conductors must have the minimum ampacity of 1/10th of the protective device from which the tap is being made.
The second tap rule is for a 25-foot long tap, and in my experience this is the most common tap rule that I have seen applied. Here the intent is to have the conductors extend from the tap location to another piece of equipment. There are three simple rules: the ampacity of the conductors is at least 1/3 of the protective device ahead of the tap; the conductors terminate in a single overcurrent device that limits the load they can carry; and the conductors are protected in an approved raceway or other means. As I mentioned, this is the most common tap used in my experience. It is commonly used in a case where the equipment has a load that is not close to its rating, but there is no more room for sub-feed devices. We had a situation years ago in a commercial laundry where a 1200-amp switchboard fed several pieces of equipment, and they needed to install some additional washers. The actual load on the 1200-amp board was only about 700 amps, but there was no remaining space for additional overcurrent units. The solution was to use the 25-foot tap rule and install a panelboard with a main breaker. The trick was that there was a door right next to the 1200-amp unit, so by the time we made the tap, ran the conduit, and set the new panel on the other side of the door, the 25-foot rule barely made it.
The third tap rule deals with transformer taps which include the primary and secondary conductors in the 25-foot allowance. The fourth rule provides an allowance for taps over 25 feet when applied in high bay manufacturing buildings where the walls are 35 feet tall, which would make overhead taps impossible under the other rules when the distance from the tap to a piece of equipment is over 25 feet. Again there are specific conditions to follow for each rule, so please review them. The last feeder tap rule is for outside taps, while the taps covered so far are assumed to be inside facilities. However, if the taps are located outside of a building or structure, the tap can be unlimited in length. Please read the details in 240.21(B)(5).
Photo 2. In this condition, if the feeders to this transformer were taps then according to 240.21(B)(3) the length of the transformer feeders and the secondaries together shall not be over 25 feet in length.
Rules for Protection
In 240.21(C) through (H), rules for protection of transformer secondaries, service conductors, busway taps, motor circuits, generators and battery conductors are covered. In keeping with the combination inspector direction of these articles, I have just detailed the most common cases. I’ve never tried to memorize any of the tap rules, as there are simply too many details and conditions, so please remember to utilize the code book and check each installation you are inspecting.
Locations and Accessibility
Next we will jump to 240.24 Location in or on Premises. We will hit the highlights here, the first being that the overcurrent devices have to be readily accessible and shall be installed so that the center of the grip of the operating handle is not more than 6 feet 7 inches in its highest position from the floor or working platform. This is an enforcement issue and is often caught in the field.
In (B) we discover that each occupant shall have ready access to the overcurrent devices protecting the conductors supplying that occupancy, and this applies to both residential and commercial. We have a couple of conditions which may modify this. One is a facility that has continuous electrical building maintenance and supervision, and this may apply to various facilities such as guest rooms or similar locations. The overcurrent devices shall be located where they will not be subject to physical damage. This may be a judgment call, but one that comes to mind is storage facilities which set their electrical equipment on the outside of the storage buildings where they are subject to damage by various vehicles. Here we usually use some type of bollard to provide the protection needed.
The last three conditions for locations requires the locations not to be near ignitible materials, not to be located in bathrooms of dwelling units, dormitories, guest rooms or guest suites, and the last condition to avoid is over steps or stairs. The thought here is that we want to provide a stable and level working area for anyone who may have to service or operate the overcurrent devices.
Photo 3. Here is an example of providing physical protection to this equipment by the use of bollard posts.
Plug Fuses, Fuseholders and Adapters
In Part V of Article 240 we have requirements for Plug Fuses, Fuseholders, and Adapters. We will cover this since many of the combination inspectors working in parts of the country that have older facilities may still find in-use plug fuses, more commonly referred to as screw-in fuses. First is a limitation that these will only be used on circuits not exceeding 125 volts between conductors or on a system having a neutral point where the line-to-neutral voltage doesn’t exceed 150 volts. This really applies only to branch circuits. Each fuse and, if used, adapter will be marked with its ampere rating. Further, if 15 amps or lower, they will be identified by a hexagonal configuration of the window or other prominent part to allow them to be identified from other fuses of higher ratings.
Next, we need to visit some screw-in fuse basics. First, they shall have no exposed energized parts after the fuses have been installed, and second, the screw shell they screw into shall be connected to the load side of the circuit. With this, let’s consider this further. If the screw shell was connected to the line side of a circuit and you screwed in a fuse, if your fingers contacted the outer portion of the fuse you would get shocked. So this is a critical requirement to make sure the screw shell is not energized until the fuse has been completely installed.
Photo 4. Edison-base fuses are shown in the bottom four examples; please note the hexagonal configuration of the 15 amp units. The top fuses are examples of Type S fuses with the appropriate adapter shown in the middle; note the spring tang which prevents the adapter from being unscrewed once installed.
Edison-base fuses are covered in 240.51; however, these are only to be used for replacements in existing installations where there is no evidence of overfusing or tampering. This is because Edison-base fuses are totally interchangeable, so you can replace a 15-amp fuse with a 20-amp fuse or a 30-amp fuse. That interchangeability leads to applications where misapplications may occur due to availability issues or ignorance of proper circuit protection.
So to solve this issue, Type S Fuses were invented to limit the size of the fuse that can be installed through unique physical dimensions to the screw portion of the device. This is covered in 240.53 and they have three ranges 0–15, 16–20 and then 21–30 amps. This makes it so they are not interchangeable; and if you have a circuit which is using 20-amp conductors, you can’t install a 30-amp fuse. Now to follow up with this additional safety provision, they made adaptors for Type S Fuses so they could be installed in standard Edison-base fuse holders. These adapters have a spring tang on them so that once an adapter has been installed it can’t be removed, thus providing the same limitations and additional safety of the Type S fuses in older installations. These adapters are covered in Article 240.54.
Photo 5. These are renewable fuses — on top is the interior of a 200-amp fuse and below is a 20-amp fuse, as mentioned in 240.60(D).
Cartridge Fuses and Fuseholders
In Part VI we cover Cartridge Fuses and Fuseholders. In 240.60 we have general rules for cartridge fuses which cover the voltage limitations and the need for unique sizing to make it difficult to install a fuse into a fuse holder which is designed for a lower current. Also, the marking requirements are covered, which should help both the contractors and inspectors to verify we have the proper fuse for the application.
Renewable fuses are cartridge fuses which disassemble and allow one to replace the internal fuse element. As I travel around, I often ask if anyone has seen these and only those who have been in the field for some time have usually heard of them and even fewer have seen them. The last item to cover in the fuse area is that fuses that are rated 600 volts nominal or less shall be permitted to be used for voltages at or below their ratings.
Coming down to the end of overcurrent devices, we step into the circuit breakers in Part VII. Circuit breakers come in many sizes and options, and they have the ability to be reset once they are tripped if they have been installed in the proper application. Breakers shall be capable of being opened manually, and they shall clearly indicate whether they are in the open (off) or closed (on) position. If the handles operate in the vertical, then the "up” position of the handle shall be the "on” position. This is sometimes a challenge when doing service work, because some breakers have various orientations which can be used that may not provide the "on” position to be up. Breakers also have a requirement that they are not subject to tampering, or unauthorized alteration of the factory calibration, unless intended for adjustment.
Marking of breakers must show the amperage rating in a manner that will be durable and visible after installation. In some cases the marking may be under a trim or cover; however, generally the amperage is listed on the operating handle. Units made for 100 amps or less shall have this marking on the handle or escutcheon areas. The interrupting rating of breakers shall be marked on the breaker. It might be referred to as AIC (amps interrupting capacity) or IR (interrupting rating). If it is not marked, then it is assumed the breaker is only listed to be used in an installation which has an available fault current of 5000 amperes or less. This is a reminder to make sure the overcurrent devices used are listed for the available fault current at that point of the distribution system.
If a breaker is to be used as a switch, then it has to listed for this usage and the marking will either be a SWD (switched) or HID (high-intensity discharge). These applications usually happen in locations such as warehouses or small retail shops. So if the only method of turning on the lights is the breaker, then it would make sense that you have to enforce the switch rating requirement. If they are utilizing high-intensity discharge lighting, the breakers have to be marked with the HID rating.
Applications in 240.85, reminds us that we have to use breakers that are compatible with the system voltages in each installation. Please see this section of the code regarding the use of straight rated breakers and slash rated breakers. Most of us deal with solidly grounded systems, which require slash rated (120/240V or 480Y/277V) breakers.
Breaker Series Ratings
Breaker Series Ratings is found in 240.86, which allows breakers to be installed under some very special conditions. Series rating is a way to install breakers which will rely on the upstream device to protect it in the case of a high-fault current. This allows breakers that are not rated for the available fault current to be utilized only in two conditions.
One is under engineering supervision in existing installations, which at times happens when work is being done to older systems. Here the engineer who is qualified may apply a series rating if the system is properly documented and field marked to identify it is a series system.
The second is under the condition of 240.86(B), Tested Combinations, that allows series rating if the combination of devices have been tested and certified to operate together to provide the protection of the system from the available fault current. This is often done to lower the cost of the equipment package. This requires that the system be identified as a series system and the documentation is maintained on-site for the inspector and future electricians who may have to service the installation. This is a very complicated item because when it is used and any additions or modifications are made, the original requirements of the series rating still apply and must be followed.
In my jurisdiction, we had a strip mall constructed using a series rated system using brand X gear. As each individual suite had their tenant improvements done, each contractor performing the work for the new tenant had to match the exact requirements and brand of the series system. One contractor who installed brand Y sub-panels learned the hard way and had to change out two panels to keep the system installed within its series rating. If a system has a motor load connected on the load side of the higher rated device and on the line side of the lower rated device, or if the motor load is more than 1 percent of the rating of the lower rated device then a series system is not allowed to be used. So if you have a series rated system, review the code and insure the conditions are met.
The last subject to cover in this article on overcurrent protection is fairly new to the code. In 240.87, Noninstantaneous Trip, a circuit breaker may be used that doesn’t have an instantaneous trip feature or has that feature turned off. The instantaneous portion of an overcurrent device gives the device the ability to react as fast as possible to a short-circuit condition within the system. The instantaneous portion of the overcurrent devices also reduces the incident energy at a point of fault within the system.
You might ask why would we do this; in cases where breakers are used to selectively coordinate a system, the upstream device may have the instantaneous set higher or turned off so the downstream device has the time needed to operate. So as the upstream device waits for the downstream unit to do its job, the current will not be limited and will continue to flow for an extended period of time increasing the incident energy at the fault location. Under these conditions we must provide one of three equivalent means, (1) zone-selective interlocking, (2) differential relaying, or (3) energy-reducing maintenance switching with local status indicator. The purpose of these three options is to reduce the stress on the equipment but most of all for the protection of personnel who may be working on the system.
These requirements are unique to breakers and do not apply to fused systems. From my experience when we dealt with systems like this, we asked for third party verification that the electrical system was installed properly and that any adjustments to breakers were done properly and coordinated to function together. After the third party report was done, the engineer of record would review it and then submit it to the AHJ for inclusion in the approved set of plans for the project.
This concludes Article 240. I hope you have had your code book open as we continued, due to the fact that I cover only the issues which I feel you need to have a basic knowledge of as a combination inspector. It is always good for you to review the portions I skipped; this will help you when a situation may occur in your area and you will recall that you heard or read something about that, and you’ll be able to find it that much easier in the code book.
Read more by Randy Hunter