I recently purchased a house that I am fixing up for resale. I upgraded the service to 200amps and installed new main distribution panel. Approx 70% of the house has been rewired and is being fed by the new panel. Six existing 20 amp circuits are being fed by a federal pacific sub-panel.
For obvious reasons I want to replace the FPE Panel. I want to run these six circuits back to my new main panel rather than replacing the sub-panel. The new panel located 20’ away on the exterior of the house.
I would delete the sub-panel, splice the conductors and run them to the new panel in 1’ EMT
Here are the questions:
Can I just run # 12 THHN for each of these circuits or do I need to derate?
I see no problem with that plan as long as you'll have a total of 9 wires (2 hots to 1 neutral). I've seen some people here call them edison circuits. NEC calls them multiwire branch circuits and where I come from they call them networks.
If you aren't familiar with these types of circuits and the hazards of wiring them incorrectly then don't do it. You would need (12) wires in which case you'd need to derate.
You are correct. If these circuits are multi-wire circuits the neutrals don’t need to be counted but there will still be 6 current caring conductors. The ampacity of #12 THHN is 30 amps and table 310.15(B)(2)(a) specifies 80% adjustment factor for 4-6 conductors. This would result in the #12 THHN conductors having an ampacity of 24 amps. If these wires are installed in wet locations the starting ampacity of #12 THWN in 25 amps which after applying would result with an ampacity of 20 amps.
Jsimontucson,..watch your phasing when using (1)neutral per (2)hots...make sure that each corresponding phase conductor lands on a different phase...otherwise unfavorable imbalances on the neutral leg will result in overheating the neutral..Just group your breakers accordingly..."A" phase for one phase conductor,..and "B" phase for the other, and land the neutral normally.. Russ
[This message has been edited by Attic Rat (edited 03-28-2004).]
.."if it ain't fixed,don't break it...call a Licensed Electrician"