All questions and answers are based on the 2008 NEC.
Q. What are the NEC requirements on the use of the white wire for the ungrounded conductor?
A. A conductor with white insulation can only be used for the ungrounded conductor as permitted as follows [200.7(C)]:
The white conductor within a cable can be used for the ungrounded conductor if permanently reidentified at each location where the conductor is visible to indicate its use as an ungrounded conductor. Identification must encircle the insulation and must be a color other than white, gray, or green.
The white conductor within a cable can be used to supply power to single-pole, 3-way, or 4-way switch loops if permanently reidentified at each location where the conductor is visible to indicate its use as an ungrounded conductor.
The white conductor within a flexible cord can be used for the ungrounded conductor for connecting an appliance or equipment as permitted by 400.7.
FPN: Use care when working on existing systems, because a gray insulated conductor may have been used in the past as an ungrounded conductor.
The NEC doesn't permit the use of white or gray conductor insulation for ungrounded conductors in a raceway, even if the conductors are permanently reidentified (Figure).
Q. Can a GFCI receptacle be installed on an AFCI-protected circuit?
Q. In a two-family dwelling, is it legal to have the panel in one unit, so the other unit does not have access to it?
A. No, each occupant must have ready access to the overcurrent devices for their occupancy [240.24(B)].
Q. How many isolated ground receptacles can share the same isolated grounding conductor?
A. As many as you want. The Code does not provide a limitation.
Q. What is the difference between Class 1, Class 2, and Class 3 circuits?
A. 725.2 defines these circuits as:
Class 1 circuit
That wiring system between the load side of the Class 1 circuit overcurrent device and the connected equipment such as relays, controllers, lights, audible devices, etc.
Class 2 circuit
The wiring system between the load side of a Class 2 power supply and the connected Class 2 equipment. Class 2 circuits are rendered safe by limiting the power supply to 100VA for circuits that operate at 30V or less and the current to 5mA for circuits greater than 30V [Chapter 9, Table 11].
Class 3 circuit
The wiring system between the load side of a Class 3 power supply and the connected Class 3 equipment.
Class 1 nonpower-limited circuits can operate at up to 600V, and the power output isn't limited [725.41(B)]. Class 2 circuits typically include wiring for low-energy, low-voltage loads, such as thermostats, programmable controllers, burglar alarms, and security systems. This type of circuit also includes twisted-pair or coaxial cable that interconnects computers for Local Area Networks (LANs) and programmable controller I/O circuits [725.121(A)(3)]. Class 3 circuits are used when the power demand exceeds 0.50VA, but not more than 100VA, for circuits greater than 30V [Chapter 9, Table 11].
Q. Are there any rules regarding electrical outlets that are close to sinks in a school?
A. All 15A and 20A, 125V receptacles installed within 6 ft of the outside edge of a sink must be GFCI protected [210.8(B)(5)].
Q. Can we use Type NM Cable (Romex) in a four-story apartment building?
A. If your apartment building is constructed of (or permitted to be constructed of) Type III, IV, or V construction, it may be used [334.10(2)].
Q. Is there an exception to the 30-in. burial requirement for a ground ring?
A. No. A ground ring encircling the building or structure, consisting of at least 20 ft of bare copper conductor not smaller than 2 AWG, must be buried not less than 30 in. [250.53(F)].
Q. We heard you can't enter conduit on the sides of a handy box. Can you show us where it states that in the NEC?
A. The NEC contains no such requirement.
Q. Some areas of the Code state that schedule 80 PVC conduit is suitable for protection against physical damage. With that said, are the burial depths for schedule 40 and schedule 80 different?
A. No, they are the same [300.5].