Here are the latest short answers to questions posted on our Web site. In our discussion, we will cover topics from Secs. 210-4(a), 210-11(c)(3), 250-50, 250-104(a), and 310-8(d); Art. 210; and Table 250-66 of the National Electrical Code (NEC).
Q. The local inspector turned down my job for using THHN outside the weather head for service entrance conductors. He said I had to mark the conductors "sunlight resistant." I've been doing this for more than 15 years, and this is a first for me! Is he correct?
A. Yes. This is a new requirement in the 1999 NEC, added in Sec. 310-8(d). The exact text reads, "Insulated conductors and cables used where exposed to direct rays of the sun shall be of a type listed or marked 'sunlight resistant.' " According to the UL White book, page 114, THHN, THHW, and THWN conductors that comply with an artificial weathering test are marked "sunlight resistant."
Q. To quickly remove dangerous voltage resulting from a phase-to-ground fault, you must bond the interior metal water pipe system to the system grounded conductor. How is this copper bonding conductor sized? How does the size of the service affect the sizing of this bonding jumper? Must the bonding connection to the interior pipe be within 5 ft of the water pipe's point of entry into the building?
A. Because the bonding jumper must carry fault current (to assist in clearing a fault), you use the service conductor size to determine the interior metal water pipe bonding conductor. Sec. 250-104(a) specifies the bonding jumper shall be sized in accordance with Table 250-66, based on the size of the largest service-entrance conductor. Here's an example of the use of Table 250-66 for different size services: The bonding of the interior metal water pipe system is not required to be within 5 ft of the entrance of the metal water pipe into the building.
Note: The 5-ft water pipe limitations in Sec. 250-50 only apply when you use the water pipe as a conductor to interconnect electrodes that are part of the grounding electrode system.
Q. I supplied the bathroom receptacles from one circuit of No. 12/3 nonmetallic sheath cable. I used the other circuit (common neutral) to supply other loads. Does this meet NEC requirements?
A. Yes. You can use a multiwire branch circuit to supply the 20A branch circuit for bathroom receptacles, as required in Sec. 210-11(c)(3). You can find the answer in Sec. 210-4(a), which states you can use a multiwire branch circuit to supply any of the circuits required by Art. 210. This rule also considers a multiwire branch circuit as two multiple circuits.
Q. What are the NEC requirements for installation of fire and/or smoke detectors in a dwelling unit?
A. None. The NEC does not cover this subject, but the Life Safety Code NFPA-101 does.
