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Joined: May 2012
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sidmuer Offline OP
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Ok, if I have 100 AMP panel, in 60 degree ambient temperature, how would I size the wire??

Do I just do 100A x 1.25 for continuous = 125A then Table 5A says at 60 degrees using the middle column wire is .67
so then 125A / .67 = 186.5
So then I go back to table 2 using the middle column wire, I would choose 3 aught? (210AMP rated)

OR:
since 100AMP panel can use #3 rated for 105AMP. I just goto 105AMP / .67 for the 60 degree ambient temp and get: 156.7 = 2 aught (185AMP rated wire from middle column of Table 2 )

OR
is 100amp panels with #3 wire feeders only allowed for residential dwellings, and since it doesn't specify as a residential application/installation for this panel do I stick to the first method?

Thank you.

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twh Offline
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60 degree ambient is pretty warm. Do you mean 60 degree rating on the breaker?

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sidmuer Offline OP
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ambient...
it's a pen/paper test question.

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twh Offline
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I don't know that breakers are okay in a 60 degree ambient. Is it a trick? I'll give it some thought, anyway. Is it a 2012 code question?

Last edited by twh; 05/10/12 08:54 PM.
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twh Offline
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26-402 says no panels in high ambient rooms. When do I get my marks?

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Gentlemen:

Two (2) posts to this thread were deleted today. PMs were sent to the two gentlemen involved.



John
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sidmuer Offline OP
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Originally Posted by twh
26-402 says no panels in high ambient rooms. When do I get my marks?


based on 2009 CEC book.
hmm... table 5b (going off memory.. somewhere there... )
ambient adjustment factors to derate wires are listed there accordingly.
It's not for the panel, but for the wire. I guess where the wire run is happening, it can reach that temp.

Joined: May 2012
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sidmuer Offline OP
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^^ nevermind that last response. I noticed my original question was regarding panels, not wire runs!!!

Thanks twh! smile

I got an interesting one for you. It is tricky.
I gotta look it up from my notes.
Here it is....

if I have 2500 WATTS heater and 240 VOLTS. I'd like to size the conductors.
do I go about it as such:
2500 / 120 = 20.833
So, here's the part that is tricky ( to me )
Do I need to pad that wire by x 1.25 for continuous load?
If so, I get 26AMP, and it's an easy #10 AWG answer from Table 2. However, if not, I'm left with 20.8A. That means, in T2 for conductor size, I would have to pick #10 since it is over 20. BUT..... SEC 8-106(1) states that if the next smaller size conductor has not more than 5% less than this minimum, the smaller size is permitted. Since 5% of 20 would be 1, and this falling at 20.8, does that mean I can use #12 ??

Or, am I totally misunderstanding 8-106(1) rule?

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twh Offline
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Joined: Aug 2002
Posts: 402
J
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2500 watts and 240 volts = 10.4 amps

#14 and 15 amp circuit is fine even if you add the 1.25 factor which I am not sure about needing.

Last edited by jdevlin; 05/16/12 09:31 AM.
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