why can't you use 3w seu with a separate 4awg egc from a service to a subpanel [with an isolated gc]? the egc shouldn't be current carrying so there shouldn't be a problem with impedance or inductive heating... that's why we keep them in the same 4w ser cable, right?
It isn't carrying current under normal conditions. However, in the event of a fault, the fault current may be limited by the reactance of the single conductor, if it is not in close proximity to the conductor feeding the fault. The OCPD might not open in such a case.
Re: 4w ser or 3w seu#7183 01/25/0208:55 PM01/25/0208:55 PM
this was in a new house i walked through a few days ago, the meter and 200amp disconnect combo were surface mounted on the side of the garage, and the seu and 4awg cu were run across the garage in the joist bay above, and came down the wall to the 200amp loadcenter, with the isolated gc. it wasn't my job, and i didn't want to stir anything up, so didn't say anything to the contractor.... but i didn't think it was right. if i thought it was real dangerous then i would have said something, thats why i asked here, cause i wouldn't have been able to explain to him why it was a bad idea
Re: 4w ser or 3w seu#7186 01/26/0210:54 AM01/26/0210:54 AM
This is 300-3(b)(1999) Notice it says 'and all EGCs'. I haven't seen your installation but it sounds like this would cover your situation.
(b) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, trench, cable, or cord, unless otherwise permitted in accordance with (1) through (4).
Re: 4w ser or 3w seu#7187 01/26/0209:28 PM01/26/0209:28 PM
Aside from the code issue, it seems like a commonsensical thing to do,'til you get to the point of putting the wiring into the boxes. Doesn't seem likely that they could ever adequately close off the box opening, or adequately clamp the cable, with that extra conductor added to the cable. Of course, I'm sure UL hasn't tested such a set-up, so there's no way to be assured that the connection would work.
Re: 4w ser or 3w seu#7188 01/26/0210:25 PM01/26/0210:25 PM