Stumped by the Code?

Mar 1, 2006 12:00 PM, By Mike Holt, NEC Consultant

All questions and answers are based on the 2005 NEC.

Q. When wiring a circuit breaker, does the Code require supply conductors to terminate to the top (line side) of the breaker?

A. No, but if the breaker is marked with “line” and “load,” it must be installed in accordance with the manufacturer's instructions as per 110.3(B).

Q. I want to run 3/0 AWG triplex to a transformer located outdoors. Am I required to include a ground wire with the triplex even though the transformer is grounded to two ground rods?

A. Yes, an equipment grounding (bonding) conductor is required to be run to the transformer because it is needed to provide the low-impedance path to the source that is necessary to clear a ground fault [250.4(A)(3)] (Figure). Because the contact resistance to the earth via the ground rods is so high, very little ground-fault current would return to the electrical supply source via the earth. The result is the circuit overcurrent protection device will not open to clear a ground fault, and metal parts will remain energized.

Q. When the NEC requires GFCI protection for receptacles, is it required to be supplied via a GFCI receptacle?

A. No. GFCI protection can be supplied by circuit breakers or receptacles. In 210.8, the NEC states that specific receptacles must have GFCI protection for personnel — not that GFCI receptacles are required for each outlet.

Q. According to product instructions, a recessed lighting fixture is permitted to be installed in the ceiling above a shower if it's GFCI protected. But my inspector insists that it's not permitted to be installed above the shower space because it's not listed for a wet location. Is this true?

A. No. Luminaires located in bathtub and shower zones must be listed for the location. Where subject to shower spray they must be listed for wet locations [410.4(D)]. Because you are installing the luminaire in the ceiling above the shower space, it will not be subject to shower spray, therefore it only needs to be listed for a damp location. Just be sure that the luminaire is GFCI protected in accordance with the instructions [110.3(B)].

Q. If the feeder to a detached building contains a ground wire, is the detached building disconnect still required to be grounded to the earth?

A. Metal parts of electrical equipment must be grounded to the earth to reduce transient voltage on the metal parts from lightning, thereby reducing fires from a surface arc within the building or structure from a lightning event [250.4(A)(2)]. The equipment grounding (bonding) conductor contained with the feeder conductors is intended to serve as a low-impedance fault current path to the source to assist in clearing a ground fault [250.2].

Q. When a vapor barrier has been installed under a footer, can the steel rebar above the vapor barrier be used as a grounding electrode?

A. No. A concrete-encased electrode of the steel rebar type is only suitable to be used as a concrete-encased electrode if it's located within and near the bottom of a concrete foundation or footing in direct contact with the earth [250.52(A)(3)]. If a vapor barrier is installed between the footer and the earth, then the rebar can't be used as an electrode.