I have a house that is a pre-fab, the main feeds were ran after the house was put in place and go into j-boxes going to the different circuits. The feeds ( 10-15 of them ) are bundled together using zip-ties and are layed on top of the foundation wall and run the length and width of the house. I have read about the "cabling effect" where NM 14,12 or 10 awg zip-tied together over long distances can sustain a dramatic loss in the amp rating for the circuits involved. Has anybody else heard of this and if so what can you do about it?
Thanks much for the reply and calculations. I'll check out the allowed limits and see if there is a way to fan these runs out either way. I'd like my system to be as efficient and safe as possible, but I'll take what I can get!
Iwire, Don't forget that 240.4(B) does not permit using the next higher standard overcurrent device if the conductors are part of a multioutlet branch circuit supplying receptacles for cord and plug connected loads.
[This message has been edited by caselec (edited 02-14-2003).]
Curt, The circuits were not described in detail so to do any calculations I had to make some assumptions in my post I figured 12, 2 wire circuits, if he has some multiwire circuits it might help him, as for each 2 circuits on multiwire you lose 2 current carrying conductors (the neutrals). I did not bother to figure all the options.
George, When some one asks a question here I assume they want an answer as far as code, in this particular case there should not be any heating unless most or all the cables are fully loaded which is probably not going to happen, as in your example it could not happen, but whether or not you or I believe it to be a problem it's still a violation that could be failed by an inspector.
That said, I know there is a real world out there, and this kind of installation is not that uncommon
Bob Badger Construction & Maintenance Electrician Massachusetts