Jim Dollard has an extensive background in codes and standards.

If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Send questions to [email protected]. Answers are based on the 2017 NEC.


Temporary power use


Does Article 590 prohibit us from supplying power for cord-and-plug equipment that looks questionable? We were supplied with strain-relief cord connectors, cord and female cord caps to supply floor grinders. When we saw the grinders in use, it was obvious the contractor had manufactured them in the shop. There were standard start/stop enclosures along with motor starters on the portable floor grinders. They were using electrical equipment designed for a permanent installation on hand-operated portable equipment. We had concerns.


Temporary power installations must comply with all applicable NEC requirements. Article 590 contains only modifications to existing rules and supplemental requirements for temporary power installations. Your situation represents multiple violations but is not prescriptively addressed in the NEC. Section 422.6 requires all appliances operating at 50 volts or more to be listed.


This does not apply to tools. In fact, in 250.114, the NEC makes clear distinctions between listed appliances and listed tools. In temporary and permanent installations where an EC installs a receptacle, they are not responsible for what others may plug into the device. There are regulations that prohibit the use of tools as you describe. OSHA 1926.403(a) requires such a tool to be listed. The floor grinders may include listed parts, but are not listed as a portable assembly. Section 1926.403(b)(2) requires listed equipment to be used in accordance with the listing and manufacturers instructions.


Isolated ground receptacles


When applying the rules in 517.16(B)(1) 
for isolated ground (IG) receptacles, it seems we no longer need to install the equipment grounding conductor (EGC) in 517.13(B). The only grounding requirements referenced in 517.16(B)(1) 
are the isolated EGC and the metal raceway or cable that is approved as an EGC. Since we are outside of the patient care space, does that mean 517.13(B) does not apply?


No. All of the requirements of both sections 517.13 and 517.16 apply. Section 517.16 prohibits an IG receptacle within patient care vicinity, which is inside of a patient care space.


You are correct in that the text in Section 517.16(B)(1) references only the IG EGC and the requirement for metal raceway systems or cables with a metallic armor or sheath assembly referenced in 250.118. However, Section 517.16(B)(2) references the insulated copper EGC in 517.13(B)(1) and prohibits that EGC from being connected to the grounding terminals of an IG receptacle. Where an IG receptacle is permitted in a patient care space (outside the patient care vicinity), there must be three ground-fault return paths, the metal raceway or cable armor, an insulated EGC, and an IG EGC.


The confusion here seems to be the defined terms “patient care space” and “patient care vicinity.” The patient care space encompasses but is not limited to the patient care vicinity. These defined terms are extracted from NFPA 99, Health Care Facilities Code. The annex material in NFPA 99 and informational notes included in the definitions of Patient Care Space in 517.2 clarify that these spaces were formally called rooms and would include a patient care room, procedure room, treatment room and other care spaces.


EMT support


Does the NEC require electrical metallic tubing (EMT) to be securely fastened in place within 3 feet of every coupling? An inspector is quoting 358.30(A) and requiring us to support EMT within 3 feet of every coupling because this section mandates secure support at every “tubing termination.” Is that correct?


No. Section 358.30(A) requires EMT to be securely fastened every 10 feet and within 3 feet of termination. This requirement specifically calls out termination types, including outlet boxes, junction boxes, device boxes, cabinets, conduit bodies, or other “tubing termination.” The use of the term “termination” implies the conclusion or final point. The NEC does not define commonly used terms such as this one. Support requirements for other raceways include the same requirement but refer to support for “conduit termination.” The NEC does not require support within 3 feet of couplings where these raceways are installed.


Type NM cable installation


I have a question about the use of Type NM for wiring of apartments during the construction phase. I see under 334.12(B)(4), NM is not to be used in wet or damp locations. One local authority having jurisdiction will always say to wait until the building is roofed and the sheathing is applied on exterior walls before installing any NM within the building. Other areas permit us to start work once the walls are framed. This affects the project schedule significantly. Can you shed some light on this?


Section 334.12(B)(4) prohibits Type NM cable in wet or damp locations. Section 334.10(A)(1) specifically permits Type NM cable in “normally dry locations.” See the defined term “dry location” in Article 100, which clarifies that a location considered to be dry may be temporarily subject to dampness or wetness as in the case of a building under construction. In this case, you should discuss the defined term “dry location” with the local AHJ to resolve this conflict.


Increased size of EGC


We are installing multiple 20-ampere branch circuits, and, due to the long distance, the drawings specify 6 AWG to the first receptacle outlet. Each branch circuit supplies four receptacle outlets. That will require larger EGCs due to the increase to 6 AWG for voltage drop. The drawings call for 12 AWG conductors downstream of the first outlet. Do we need the larger EGC run with the branch circuit from the first outlet to the other three?


No. Section 250.122(B) requires only wire type EGCs to be proportionally increased in size where ungrounded conductors are increased in size from the minimum size that has sufficient capacity for the intended installation. This means the increase in the size of the wire type EGC applies only where there is an increase in the size of the ungrounded conductors. For the installation you described, a 12 AWG EGC is permitted from the first outlet to the remaining three receptacle outlets because, at that point, there is no increase in the size of the ungrounded conductors.


Cord through hole in cabinet?


Where a dishwasher is cord-and-plug-connected, the NEC requires that the receptacle supplying the dishwasher be located in the space adjacent to the dishwasher. The only way to do that is to drill a hole through the cabinet for the cord to get into the adjacent space. This presents a problem because our inspector prohibits a cord from being run through a hole in the wall of the cabinet. How can we possibly comply with this rule?


Section 422.16(B)(2) was revised in the 2017 NEC to provide clarity with respect to receptacle location for cord-and-plug-connected trash compactors and built-in dishwashers. The receptacle for a built-in dishwasher must be located in the space adjacent to the dishwasher. The intent of this rule is to ensure the cord for the dishwasher is run through the cabinet wall.


Section 400.12(2) prohibits power supply cords from being run through holes in walls, structural ceilings, suspended ceilings, drop ceilings and floors. While this requirement does not specifically identify “cabinet walls,” an inspector may cite this requirement to prohibit such an installation.


You have identified a situation that needs additional clarity. Cord-and-plug-connected equipment, such as built-in microwaves and dishwashers, require the power-supply cord to penetrate a cabinet for a cord-and-plug connection. An exception should be added to Section 400.12(2) to specifically permit these installations of listed appliances.


Vehicle bay?


The NEC now requires a receptacle in every vehicle bay for garages that are part of one- and two-family dwellings. What is a vehicle bay? Some garages we see are deep enough for two cars, meaning that what looks like a two-car garage from the front of the building can easily fit four cars. Does that mean we need to install four receptacles?


A review of the substantiation provided by the technical committee and submitters of public inputs that supported the insertion of “vehicle bay” instead of “car space” did not address your question specifically. However, the intent of this change is clearly to mandate that required receptacle outlets be evenly distributed in the garage space.


This revision provides significant clarity by requiring one receptacle outlet be installed in each vehicle bay. This requires an accessible receptacle outlet adjacent to each vehicle bay. This also prohibits installation of only one receptacle outlet with two duplex receptacles in a two-vehicle bay garage. A receptacle outlet is required for each vehicle bay. 


With respect to a deep garage as you describe, the existing requirement needs clarity. In my opinion, a garage with two doors that can easily fit four cars contains four vehicle bays and would require four receptacle outlets. I encourage you to get involved in the process and submit a public input to revise the NEC.