Knowing how important NEC issues are to our readers, we're introducing a new online Code Q&A column. Updated weekly, visit this link for answers to your latest Code questions and concerns.
Q. Does the NEC require you to pigtail conductors from a 2-wire circuit if more than one wire terminates on a receptacle?
A. No, pigtailing is not required for 2-wire circuits. However, for multiwire branch circuits (3-wire or 4-wire circuits) where the removal of such devices would interrupt its continuity, the continuity of a grounded (neutral) conductor cannot be dependant on device connections [300.13(B)].
Q. According to the NEC, what is the minimum height I can mount a meter enclosure above ground?
A. The NEC doesn’t specify a minimum mounting height, but you do need to comply with the mounting height requirements of the local electric utility.
Q. Are some inspectors correct in requiring green wirenuts when splicing equipment-grounding conductors?
A. No. To properly answer this question, we need to reference requirements in both the NEC and the guide information UL provides for listed products.
David Dini, P.E., senior research engineer, Underwriters Laboratories, Inc., provides this response: “Listed, insulated twist-on type wire connectors are typically available in a variety of insulation colors. However, to the best of our knowledge we have not listed a wire connector with green color insulation. Sec. 250.119 of the NEC requires covered or insulated equipment-grounding conductors to have a green or green-with-yellow-stripe outer finish, but there is no NEC requirement for the color of the insulation of a wire connector used to connect equipment-grounding conductors.
”There are some listed wire connectors of the twist-on type that are also tested and listed as grounding connectors; the listing mark information for these products will identify them as both. The insulation on these connectors (with both listings) can be various colors, except green.”
Q. Can I make splices in a conduit body, such as an LB?
A. Yes. Splices are permitted in conduit bodies, but only if the maximum number of conductors [as calculated in 314.16(B)] in the conduit body does not exceed the conduit body’s cu in. capacity, which should be marked on the outside of the conduit by the manufacturer.
Q. Can I use Type AC cable for emergency circuits in the patient care area of a walk-in clinic?
A. Yes, you can use a flexible wiring method such as Type AC interlocked cable—but not Type MC interlocked cable—with an equipment-grounding conductor in an examination room, a procedure room, or an X-Ray room of a medical facility [517.13(A)]. However, the Code does not permit a flexible wiring method for emergency circuits in a hospital [517.30(C)(3)].
Q. What is the minimum mounting height above the floor level for switches, receptacles, telephone and cable outlets?
A. None. The NEC does not contain any minimum mounting height for these outlets.
Q. What is the minimum mounting height for the service disconnecting means of a residential dwelling-unit, commercial office, or industrial factory?
A. The NEC does not specify a minimum mounting height, but 550-32(F) requires the service disconnecting means for mobile homes to be installed so the bottom of the enclosure containing the disconnecting means is no less than 2 ft above finished grade or working platform. This does not apply to any other occupancy.
The disconnecting means must also be installed so the center of the grip of the operating handle, when in the highest position, will not be more than 6 ft 7 in. above the finished grade or working platform (404.8).
Q. I’m installing a wall sconce light in a retail store. Does the NEC specify a minimum mounting height?
A. No, but where the American Disabilities Act is applicable, Section 4.4.1 states that “no object mounted between 27 in. and 80 in. above finished floor is permitted to protrude more than 4 in. from the wall.”
Q. Does the Code require me to install insulated grounding (isolated ground) receptacles in health care facilities?
Q. As long as you’re still able to reach the circuit breakers, can you mount a panel above a transformer?
A. Maybe. Per 110.26(A), you must leave sufficient workspace in front of all electrical equipment likely to require examination, adjustment, servicing, or maintenance while energized. This working space area may be no less than 2 ½ ft wide, 6 ½ ft high, and 3 ft deep. However, equipment associated with the electrical installation located above or below electrical equipment is permitted, as long as it does not extend more than 6 in. beyond the front of the electrical equipment [110.26(A)(3)].
Q. Does the restriction on branch circuit wiring in 517.13 apply to the offices, corridors, lounges, day rooms, dining rooms or similar areas at patient care facilities?
A. No. Although 517.13 contains stringent requirements on branch-circuit wiring in patient care facilities, including a requirement to install an equipment-grounding conductor in the raceway and the prohibition of interlocked MC cable with an insulated equipment-grounding conductor, its wiring methods do not apply to offices, corridors, lounges, day rooms, dining rooms, or similar areas not classified as patient care areas [517.10(B)(1)].
Q. Can a service raceway and building sewer pipe be installed in the same trench?
Q. Does the NEC require a hospital-grade receptacle in the patient care area of a walk-in medical facility that’s only open 18 hr per day?
A. No, hospital-grade receptacles are not required in such a patient care area. They are only required in locations equipped with patient beds [517.18(B) and 517.19(B)].
Q. Is it true the maximum allowable voltage drop for a lighting circuit is 5%?
A. No, the NEC does not have any rule requiring a maximum voltage drop percentage for lighting loads. However, 110.3(B) does require you to install all equipment in accordance with the manufacturer’s instructions. Typically, equipment manufacturers specify their equipment may not be connected to a circuit where the voltage drop is more than 10% of the equipment’s voltage rating. For example, a 230V lighting load may not be connected to a voltage source of less than 207V.
Q. Does the NEC require you to install a ground rod at each 30-ft light pole in a parking lot?
When you find yourself stumped by the Code, just e-mail your question to Mike Holt for future consideration in our Code Q&A.