Romex temperature adjustment

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zcanyonboltz

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Can you use the 90C column to adjust ampacity of romex? I have a practice question asking what the ampacity of 8-3 is in a 130F attic. I adjusted using 60C column from 310.15 (B) (16) and 310.15 (B) (2) (a). My answer keys uses the 90C column from both tables, is using the 90C column okay? Thanks
 
Using the tables in the 2008 NEC, I got the following:

#8 NM uses 90*C column per 334.112

table 310.16 gives ampacity of 55A.

0.76 multiplier for 123-131*F ambient

55x0.76=41.8A

No derating factor for 3 or fewer CCC (table 310.15 (B(2)(A))

MOCP=40A
 
That is the correct answer all the same numbers and as the 2014 NEC. I see that 334.112 states romex insulation shall be rated 90C. The only thing I question now is that 110.14 (C) (1) (a) says for 100A or less and 14 AWG through 1 AWG to use the 60C column unless 110.14 (C) (1) (a) (3) is used and this assumes the terminations are rated to 75C. Thanks for the replies.
 
zcanyonboltz said:
That is the correct answer all the same numbers and as the 2014 NEC. I see that 334.112 states romex insulation shall be rated 90C. The only thing I question now is that 110.14 (C) (1) (a) says for 100A or less and 14 AWG through 1 AWG to use the 60C column unless 110.14 (C) (1) (a) (3) is used and this assumes the terminations are rated to 75C. Thanks for the replies.
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yes , nm has to use the 60*C column overall,meaning you cant put #8nm on more than a 40A breaker. in this case you can still use the 40, but if your ambient were , say, 150*F and you had 10CCC together, you'd be lucky to be able to use a 20A breaker. Derating takes place from the 90*C column.
 
I've got one more thought on this...if the conductors are going in a raceway in a wet location like undeground can 90c column still be used for derating and the select conductor size from 75c column. XHHW-2 comes to mind l know the -2 allows us to use the 90c column to derate in a wet or dry location but in conductors not rated for wet location can the 90c column be used to derate? Thanks
 
zcanyonboltz said:
I've got one more thought on this...if the conductors are going in a raceway in a wet location like undeground can 90c column still be used for derating and the select conductor size from 75c column. XHHW-2 comes to mind l know the -2 allows us to use the 90c column to derate in a wet or dry location but in conductors not rated for wet location can the 90c column be used to derate? Thanks
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Uh, beyond the derating question, you cannot legally install dry location only conductors in a wet location, so using the 90C is a no go from the start.:)
 
jumper said:
Uh, beyond the derating question, you cannot legally install dry location only conductors in a wet location, so using the 90C is a no go from the start.:)
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Yea for sure, my wording may be unclear. XHHW-2 is rated for wet location and is also rated to 90C so you could derate from the 90C column as opposed to THWN you would have to derate from 75C column in a wet location?
 
zcanyonboltz said:
Yea for sure, my wording may be unclear. XHHW-2 is rated for wet location and is also rated to 90C so you could derate from the 90C column as opposed to THWN you would have to derate from 75C column in a wet location?
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No, -2 conductors are derated from the 90C for both wet and dry locations. Final ampacity is still determined by the terminals and such.
 
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