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Stumped by the Code?

Mar 1, 2007 12:00 PM, By Mike Holt, NEC Consultant

All questions and answers are based on the 2005 NEC.

Q. Does the Code require bonding around raceway knockouts for 277V or 480V feeders and branch circuits?

A. You must bond metal raceways or cables, containing 277V or 480V circuits, terminating at ringed knockouts to the metal enclosure [250.97] with a bonding jumper sized in accordance with Table 250.122, based on the rating of the circuit overcurrent protection device [250.102(D)] (Figure). A bonding jumper isn't required where ringed knockouts aren't encountered, or where the box is listed to provide a permanent and reliable electrical bond [250.97 Exception].

Q. If a generator provides a building with temporary power for construction, does the neutral have to be bonded to the case of the generator?

A. When a generator provides the sole power for a building or structure, it's defined as a separately derived system, even though no transfer switch is present [see Art. 100, separately derived system]. Therefore, you must use a system bonding jumper to bond metal parts of the generator to the grounded neutral conductor [250.30(A)(1)]. This ensures that dangerous voltage from a ground fault can be quickly removed by opening the generator's overcurrent protection device [250.2(A)(3)].

Q. How do you determine the maximum length of track lighting that you can install on a 20A, 120V circuit?

A. The rule for circuiting track lighting simply prohibits the connected load on lighting track from exceeding the rating of the track [410.101(B)]. This means you cannot connect 15A lighting track to a 20A circuit. The rule that requires a calculation of 150VA for every 2 feet of track applies only to service and feeder calculations, not branch circuits [220.43(B)]. So there is no calculation on the maximum length of track lighting on a circuit.

Q. Do I have to bond a metal fence to the pool grounding grid if it's located within 5 feet of an outdoor swimming pool?

A. All fixed metal parts located within 5 feet horizontally of the inside walls of a permanently installed pool, outdoor spa, or outdoor hot tub — and within 12 feet measured vertically above the maximum water level of a permanently installed pool, outdoor spa, or outdoor hot tub, or any observation stands, towers, platforms, or any diving structures — must be bonded together and to the bonding grid [680.26(B)(5)].

Q. Am I allowed to install 480V power conductors with 120V lighting conductors?

A. Power conductors of different systems can occupy the same raceway, cable, or enclosure if all conductors have an insulation voltage rating not less than the maximum circuit voltage [300.3(C)(1)].

Q. Must I use a common trip breaker for all multiwire branch circuits to shut off all of the phase conductors?

A. Per the NEC, you must provide multiwire branch circuits that supply switches, receptacles, or equipment on the same yoke with a means to disconnect simultaneously all ungrounded conductors that supply those devices or equipment at the point where the branch circuit originates [210.4(B) and 210.7(B)]. You can accomplish this by using single-pole circuit breakers with handle ties identified for the purpose or a 2- or 3-pole breaker with common internal trip [240.20(B)(1)].

Q. Are GFCI-type receptacles permitted on a circuit that has AFCI protection?

A. Yes.

Q. In industrial applications, is GFCI protection required for the outdoor 15A, 125V receptacles?

A. All 15A and 20A, 125V receptacles installed outdoors in public spaces used by, or accessible to, the public must be GFCI protected. GFCI protection isn't required for receptacles where the general public doesn't have access [210.8(B)(4)].

Q. Can you install electrical wires and pneumatic tubing in the same raceway?

A. Raceways are designed for the exclusive use of electrical conductors and cables, and cannot contain nonelectrical components like pipes or tubes for steam, water, air, gas, drainage, etc. [300.8].

Q. Does the NEC require GFCI protection for a drinking water cooler in an office break room that also features a sink and a microwave?

A. GFCI protection is not required for 15A and 20A, 125V receptacles in employee break rooms containing portable cooking appliances, because they are not “kitchens,” as defined in 210.8(B)(2). There are no requirements for drinking water coolers, regardless of location.

Q. What are the requirements for securing Type NM Cable?

A. You must use staples, straps, cable ties, hangers, or similar fittings to secure Type NM so that the cable will not be damaged. Secure Type NM cable within 12 inches of every box, cabinet, enclosure, or termination fitting and at intervals not exceeding 4.5 feet. You're not permitted to staple on edge two-wire (flat) NM cable.

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