Topics discussed in our "Code Forum" column involve complicated issues requiring extensive analysis. However, not every Code question warrants such in-depth treatment. Here are the latest short answers to questions posed on our Web site. Coverage includes topics in: Sec. 210-8(b), 250-24(a)(5), 250-28(d), 250-142(b) Ex. 2, 305-6, 336-5(a)(1), 336-18, 336-26, 338-4(a), and 370-23(a).
Q. I have a 600A, 120/208V, 3-phase, 4-wire main service switch fed with two sets of 350 kcmil parallel conductors. Following Sec. 250-28(d), I used a 2/0 main bonding jumper in the service enclosure. The main feeds a gutter with the same parallel make up of 350 kcmil conductors. Off this, I installed a utility meter enclosure with a 200A disconnect switch fused at 200A. The inspector says I need to bond the neutral in the 200A disconnect. I've already bonded it at the 600A switch. What do you recommend?
A. You're fine. What the inspector asks for is a violation of the main rule in Sec. 250-24(a), although probably permitted in this case in Sec. 250-24(a)(5), by virtue of the allowance in Sec. 250-142(b) Ex. 2. That said, 200A meter cans routinely have the neutral factory bonded to the can. Usually this question is reversed; someone has such a can and the inspector doesn't want it bonded; that's why the allowance for downstream meters went into Sec. 250-142 in the first place. Perhaps the inspector would be satisfied with an equipment bonding jumper across that meter can.
Q. I have a three-story apartment building with one building feeder (2000A, 208Y/120V, 3-phase) going to main switchgear breakers and then through distribution breakers to two sets of apartment metering. From the meters, it's proposed to use SER cable installed above the false ceiling and into the apartments and down the drywall to each apartment subpanel. Do Art. 336, 338, and 400 apply to SE cable? Can I use SER cable between a suspended ceiling and the fixed ceiling out of sight in this case? What other Code rules might apply to the SER cable?
A. Art. 338 applies, since this is the named article for the wiring method. Art. 400 only applies to flexible cords, and has no bearing here. By way of Sec. 338-4(a), all of Parts A and B of Art. 336 do apply, however. This brings in the three-story limitation in Sec. 336-5(a)(1) (which you meet) and the support rules in Sec. 336-18.
Be careful in calculating ampacities for this cable. The 60DegrC ampacity column limitation in Sec. 336-26 applies to this cable for the first time. For example, to run a 100A feeder to an apartment, you'd need 1/0 Al SER cable; even if the cable carried the typical XHHW designation. This rule used to be tucked away in Part C of Art. 336, but the 1999 NEC split the 1996 NEC wording, and this part of it ended up in Part B (affecting Art. 338). And, don't even think about using Sec. 310-15(b)(6) (old Note 3) because these feeders don't originate in a single-phase distribution.
Q. Where is a GFCI needed in an industrial receptacle?
A. You need GFCI protection for 15A and 20A 125V (single-phase) receptacles in bathrooms and on rooftops, per Sec. 210-8(b). You'll also need GFCI protection for similar receptacles (plus 30A receptacles) whenever temporary usage involves "construction, remodeling, maintenance, repair, or demolition" as covered in Sec. 305-6, unless your industrial occupancy meets the maintenance and supervision test in Sec. 305-6(a) Ex. 2. In addition, you need to provide GFCI protection for higher rated receptacles employed for similar temporary usage.
If you're involved with the higher rated receptacles, or if your industrial firm uses Sec. 305-6(a) Ex. 2, then you need to enter an Assured Equipment Grounding Conductor Program, as covered in Sec. 305-6(b), if you don't use GFCI protection. This is a paperwork nightmare, but as you move to the higher receptacle ratings, you'll find it's the only alternative. Current product standards don't allow for a 277V GFCI receptacle, for example, because at that voltage to ground the acceptable time/current curves for 125V devices no longer apply.
Q. Does the Code dictate the minimum distance you can install a junction box feeding a 224 light troffer?
A. No minimum distance applies. I can think of many instances where I mounted such a box directly on the back of the fixture, with a chase nipple into the ballast channel. Make sure you secure the box well, per Sec. 370-23(a).