Code Quandaries

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

Stumped by the Code?

All questions and answers are based on the 2005 NEC.

Q. Since the neutral is bonded to the case at the meter enclosure, do I still need to bond the neutral at the service disconnect?

The main bonding jumper must be used to connect the equipment grounding conductor (metal enclosure) to the grounded (neutral) conductor in a service disconnect.

A. Yes. You must install a main bonding jumper between the neutral terminal and the metal parts of the service disconnecting means enclosure in accordance with 250.24(C) [250.24(B)].

Q. I have a small metal shed located about 10 feet from a swimming pool. Am I required to bond the metal shed to the pool's equipotential grounding grid?

A. No. Only the fixed metal parts within 5 feet horizontally of the inside walls of the pool and 12 feet vertically above the maximum water level of a permanently installed pool, outdoor spa, or outdoor hot tub need to be bonded to the equipotential grid required in 680.26(C) [680.26(B)(5)].

Q. Is AFCI protection of branch circuits required for hotel/motel rooms?

A. No. AFCI protection is only required for 15A or 20A, 120V branch circuits that supply outlets in dwelling unit bedrooms [210.12(B)]. Article 100 defines a dwelling unit as a single unit that provides independent living facilities for persons, including permanent provisions for living, sleeping, cooking, and sanitation. So if the hotel or motel room provides suites or extended stay accommodations, which include permanent provisions for living, sleeping, cooking, and sanitation, then it's considered a dwelling unit per Art. 100.

Q. Can I use 105°C conductors in a PVC raceway that is marked for use only with conductors having a maximum rating of 90°C?

A. Yes. But the load on the conductors must be limited to the 90°C column of Table 310.16 so that the operating temperature of the conductors will not exceed the 90°C temperature rating of the conduit [352.12(E)].

Q. I have a 50A receptacle for a range that says the terminations are rated for 75°C conductor sizing. I used 8 AWG Type NM cable, with 90°C conductors, and the inspector failed me. Where did I go wrong?

A. The ampacity for conductors contained in Type NM cable is based on the 60°C rated column of Table 310.16, not the 90°C insulation rating of the conductors [334.80]. According to Table 310.16, 8 AWG is only rated 40A in the 60°C column; therefore, you would be OK if a 40A device protected the circuit. However, the largest range permitted on a 40A circuit would be 16kW, as per Table 220.55. Column C demand load for one 16kW range using Note 1 would be 9.6kW, and this works out to be 40A at 240V.

Q. Can I install a single receptacle in a kitchen for a microwave appliance without GFCI protection?

A. It depends on where the receptacle is located. In dwelling units, GFCI protection is required for 15A and 20A, 125V receptacles that are installed to serve countertop surfaces [210.8(A)(6)]. If the receptacle for the microwave is installed so that it does not serve countertop surfaces, you are good to go, but be sure that the receptacle, circuit conductors, and protection device are sized in accordance with the manufacturer instructions (typically 20A). However 15A and 20A, 125V receptacles in commercial kitchens must be GFCI protected even if they are not serving the countertop surfaces [210.8(B)(2)].

Q. Does the NEC require a specific coloring scheme for circuits?

A. The neutral conductor must be identified with the color white or gray. For sizes larger than 6 AWG, marking tape or other identification is permitted, but for 6 AWG and smaller the insulation must have a white or gray finish color [200.6]. The equipment grounding conductor must be green or green with one or more yellow stripes if the conductor is insulated [250.119].

On a 4-wire, delta-connected, 3-phase system, where the midpoint of one phase winding is grounded, the conductor with 208V (voltage-to-ground) must be durably and permanently marked by an outer finish orange in color, or other effective means. Such identification must be placed at each point on the system where a connection is made if the neutral conductor is present [110.15, 215.8, and 230.56].

Where the premises wiring system contains branch circuits supplied from more than one voltage system, each ungrounded conductor, where accessible, must be identified by system. The means of identification must be posted at each branch-circuit panelboard [210.5(C)]. Electricians often use the following color system for power and lighting conductor identification:

120/240V single-phase — black, red, and white
120/208V, 3-phase — black, red, blue, and white
120/240V, 3-phase with high-leg — black, orange, blue, and white
277/480V, 3-phase — brown, orange, yellow, and gray; or, brown, purple, yellow, and gray