NEC Questions and Answers

By Mike Holt for EC&M Magazine

Q1. If a generator provides a building with temporary power for construction, does the neutral have to be bonded to the case of the generator?
A1.  When a generator provides the sole power for a building or structure, it’s a separately derived system, even though no transfer switch is present [Article 100, separately derived system]. A system bonding jumper must be used 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)]. Graphic

Q2. If the secondary conductors of a transformer are less than 10 feet in length, do the secondary conductors have to terminate in a main breaker?
A2. Secondary conductors can be run up to 10 ft without overcurrent protection if they comply with 240.21(C)(2), but overcurrent protection is required for lighting and appliance branch-circuit panelboards, and this protection is required to be located on the secondary side of the transformer [408.36(D)]. Graphic

Q3. How do we determine the maximum length of track lighting that can be installed on a 20A, 120V circuit?
A3.  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 15A lighting track cannot be connected to a 20A circuit. The rule that requires a calculation of 150 VA for every two 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.

Q4. Do I have to bond a metal fence to the pool grounding grid if it’s within five feet of an outdoor swimming pool?
A4. All fixed metal parts located within 5 ft horizontally of the inside walls of a permanently installed pool, outdoor spa, or outdoor hot tub, and within 12 ft 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)].

Q5. Am I allowed to install 480V power conductors with 120V lighting conductors?
A5.  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)].

Q6. Must I use a common trip breaker for all multiwire branch circuits to shut off all of the phase conductors?
A6. Multiwire branch circuits that supply switches, receptacles, or equipment on the same yoke must be provided 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)]. This can be accomplished by 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)].

Q7. Are GFCI type receptacles permitted on a circuit that has AFCI protection?
A7. Yes.

Q8. In industrial applications, is GFCI protection required for the outdoor 15A, 125V receptacles?
A8. All 15 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)].

Q9. Can electrical wires and pneumatic tubing be installed in the same raceway?
A9. Raceways are designed for the exclusive use of electrical conductors and cables, and cannot contain nonelectrical components, such as pipes or tubes for steam, water, air, gas, drainage, etc [300.8].

Q10. Does the Code require bonding around raceway knockouts for 120V, 208V, or 240Vfeeders and branch circuits?
Q10. All metal parts intended to serve as the effective ground-fault current path, such as raceways, cables, equipment, and enclosures must be bonded together to ensure they have the capacity to conduct safely any fault current likely to be imposed on them [250.96(A)]. If the knockouts are damaged, the integrity of the fault current path is jeopardized and must be bonded around. If the knockouts are not damaged, no extra bonding is required.

Q11. Does the Code require bonding around raceway knockouts for 277V or 480V feeders and branch circuits?
A11. Metal raceways or cables, containing 277V or 480V circuits, terminating at ringed knockouts must be bonded 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)]. 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].

Q12. Does the NEC require GFCI protection for a drinking water cooler in an office break room that has a sink and a microwave?
A12. GFCI protection is not required for 15 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.

Q13. What are the requirements for securing Type NM Cable?
A13. Staples, straps, cable ties, hangers, or similar fittings must secure Type NM so that the cable will not be damaged. Type NM cable must be secured within 12 in. of every box, cabinet, enclosure, or termination fitting and at intervals not exceeding 41⁄2 ft. Two-wire (flat) NM cable is not permitted to be stapled on edge.