AFCI compatability w/shared neutral feeds?

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Re: AFCI compatability w/shared neutral feeds?

#14, #12, and #10 AWG are already derated substantially-- and they want more?

:) :( :D ;) :p :cool: :roll:
 
iwire

iwire

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Re: AFCI compatability w/shared neutral feeds?

Originally posted by tonyi:
The specs indicated you had to derate it as if it were 4 current carrying conductors in pipe though. Similar configurations in MC have existed for quite a while now too.
Click to expand...
That is true, but with 4 current carrying conductors you adjust the ampacity to 80% of the value shown in 310.16 90C column,(NM is 90C rated) which for 12 AWG NM would be 30 amps.

30 x .8 = 24 amps, so it would still be fine to use a 20 amp breaker. :)

Bob
 
tonyi

tonyi

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Re: AFCI compatability w/shared neutral feeds?

BUT! now you get to possibly derate yet again for ambient temps in a hot attic... I've measured 130F in the attic in my mom's place in south florida on a no breeze 85F day. On a windless 95F day I imagine it could go over 140F in spots. 4-6 current carrying with a 51-55C (123-131F) ambient turns that original #12 30A ampacity into only 18A ampacity after all the corrections have been applied. In this sort of environment, that 12-2-2 will require a 15A breaker.
 
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sfav8r

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Re: AFCI compatability w/shared neutral feeds?

Originally posted by tonyi:
BUT! now you get to possibly derate yet again for ambient temps in a hot attic... I've measured 130F in the attic in my mom's place in south florida on a no breeze 85F day. On a windless 95F day I imagine it could go over 140F in spots. 4-6 current carrying with a 51-55C (123-131F) ambient turns that original #12 30A ampacity into only 18A ampacity after all the corrections have been applied. In this sort of environment, that 12-2-2 will require a 15A breaker.
Click to expand...
90C (the typical rating of NMC) is 194F. If the attic is that hot, it's time for a venting fan ;)
 
don_resqcapt19

don_resqcapt19

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Re: AFCI compatability w/shared neutral feeds?

sfav8r,
90C (the typical rating of NMC) is 194F.
Click to expand...
Adjustment for high ambient temperatures starts at 31?C. The ampacity of a 90?C conductor installed in a 90?C ambient is zero.
Don

[ September 24, 2005, 01:01 PM: Message edited by: don_resqcapt19 ]
 
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