Your most pressing National Electrical Code (NEC) questions answered
All questions and answers are based on the 2011 NEC.
Q. What are the Code rules for identifying circuit conductors?
A. The neutral conductor of a branch circuit must be identified in accordance with 200.6 [210.5(A)]. Equipment grounding conductors can be bare, covered, or insulated. Insulated equipment grounding conductors size 6 AWG and smaller must have a continuous outer finish either green or green with one or more yellow stripes, in conformance with 250.119 [210.5(B)]. On equipment grounding conductors 4 AWG and larger, insulation can be permanently reidentified with green marking at the time of installation at every point where the conductor is accessible [250.119(A)]. Ungrounded conductors must be identified as follows [210.5(C)]:
• If the premises wiring system contains branch circuits supplied from more than one voltage system, then each ungrounded conductor must be identified by phase and system at all termination, connection, and splice points.
• Identification can be by color coding, marking tape, tagging, or other means approved by the AHJ.
• The method of identification must be documented in a manner that’s readily available or permanently posted at each branch circuit panelboard.
Here are some additional points to keep in mind:
• When a premises has more than one voltage system supplying branch circuits, the ungrounded conductors must be identified by phase and system. This can be done by permanently posting an identification legend that describes the method used, such as color-coded marking tape or color-coded insulation.
• Conductors with insulation that’s green or green with one or more yellow stripes can’t be used for an ungrounded or neutral conductor [250.119].
Although the NEC doesn’t require a specific color code for ungrounded conductors, 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 — black, orange, blue, and white
277/480V, 3-phase — brown, orange, yellow, and gray; or, brown, purple, yellow, and gray
Q. What are the Code rules for the overcurrent protection of panelboards?
A. Each panelboard must be provided with overcurrent protection located within, or at any point on the supply side of, the panelboard. The overcurrent device must have a rating not greater than that of the panelboard, and it can be located within or on the supply side of the panelboard [408.36].
Exception No. 1: Individual overcurrent protection isn’t required for panelboards used as service equipment in accordance with 230.71.
When a panelboard is supplied from a transformer, as permitted in 240.21(C), the overcurrent protection for the panelboard must be on the secondary side of the transformer. The required overcurrent protection can be in a separate enclosure ahead of the panelboard, or it can be in the panelboard [408.36(B)].
Plug-in circuit breakers that are back-fed from field-installed conductors must be secured in place by an additional fastener that requires other than a pull to release the breaker from the panelboard [408.36(D)]. The purpose of the breaker fastener is to prevent the circuit breaker from being accidentally removed from the panelboard while energized, thereby exposing someone to dangerous voltage. For photovoltaic systems, conductors from the PV AC inverter is permitted to backfed dedicated circuit breakers that aren’t marked “line” and “load” [705.12(D)(5)]. Caution: Circuit breakers marked “line” and “load” must be installed in accordance with listing or labeling instructions [110.3(B)]; therefore, these types of devices must not be back-fed.
Q. In a major repair garage where gasoline or gaseous fuels are not dispensed, what are the classification rules?
A. In major repair garages, if gasoline or gaseous fuels, such as natural gas, hydrogen, or LPG, won’t be dispensed, the classification rules in (1), (2), and (3) apply [511.3(C)]:
1) Floor areas.
Ventilation provided. The floor area can be unclassified if there’s a minimum of four air changes per hour for each square foot of floor area.
Ventilation not provided. The entire floor area is classified as Class I, Division 2 up to 18 in. above the floor.
2) If vehicles fueled with natural gas or hydrogen are repaired or stored, the area within 18 in. of the ceiling is classified in accordance with (a) and (b).
a) Ventilation provided. The ceiling area is unclassified if ventilation is provided from not more than 18 in. from the highest point in the ceiling to exhaust the ceiling area at a rate of at least 1 cfm/sq ft at all times that the building is occupied, or when vehicles using lighter-than-air gaseous fuels are parked below this area.
b) Ventilation not provided. The ceiling area is classified as Class I, Division 2.
3) Pit areas in lubrication or service room. The pit area is classified as provided in (a) or (b).
a) Ventilation provided. The pit area is classified as Class I, Division 2 if there’s a minimum of six air changes per hour.
b) Ventilation not provided. The pit area is classified as Class I, Division 1 up to the floor level.