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 99 188.8.131.52.7.1(A) and 184.108.40.206.7.1(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