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#36023 03/27/04 08:54 PM
Joined: Mar 2004
Posts: 3
J
Junior Member
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?

Are there any other pitfalls to this plan??

#36024 03/27/04 11:33 PM
Joined: Jan 2004
Posts: 615
J
Member
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.

BTW you could fit those in 3/4" EMT.

#36025 03/28/04 10:39 AM
Joined: Jan 2004
Posts: 91
R
Member
i would also add a ground wire for the circuits and pigtail a jumper the junction box(if metal). i'm not sure if one ground wire would be enough for all 6 circuits

#36026 03/28/04 10:57 AM
Joined: Dec 2000
Posts: 4,287
Member
The extra ground wire is really not necessary, but couldn't hurt.
One ground wire would be enough for 6 circuits or 60 circuits.

#36027 03/28/04 08:05 PM
Joined: Dec 2003
Posts: 524
Member
... Even if he pulls (9) wires in that pipe, doesn't he still have to derate,being that there are more than (3)current carrying conductors in that raceway???
Russ


.."if it ain't fixed,don't break it...call a Licensed Electrician"
#36028 03/28/04 08:35 PM
Joined: Jan 2004
Posts: 615
J
Member
I don't have this suff memorized but I'll have a go...
3-6 80%
7-9 70%
10- ?? 50%

but table 310-16 says # 12 copper thhn is rated for 30 amps. meaning you can put (30 amps times 70% = 21 amps) 21 amps.

The note at the bottom the table is for overcurrent protection.

NEC 99

Okay I did have to look up the table.

#36029 03/28/04 08:38 PM
Joined: Apr 2002
Posts: 558
C
Member
Attic Rat

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.

Curt


Curt Swartz
#36030 03/28/04 08:56 PM
Joined: Dec 2003
Posts: 524
Member
...Thanx guys,.. [Linked Image] [Linked Image]

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"
#36031 03/29/04 12:54 PM
Joined: Nov 2002
Posts: 456
C
Member
Why not run ONE neutral, and ONE ground, using the stock neutral and ground bussbars in the original panel? (of course, the neutral appropriately sized)

#36032 03/29/04 10:50 PM
Joined: Mar 2004
Posts: 3
J
Junior Member
Thank you all verry much for your help.



[This message has been edited by jsimontucson (edited 03-29-2004).]

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