Derating ampacitites, where is it??

[brother]

I know its in the code, but cant seem to locate it. where does it say that when you are derating you are allowed to use the 90 degree celcius column(the higher ampacity of the wire) to get the ampacity of it. So long as it doesnt be used pased the 75 degreee ampacity, (because of the equipment.)

for example, #12 copper is good for 30 amps. So if you have 5 ccc's in a race way and you need to derate, you would take the 30 amps X 80% = 24 amps.

this is not above the 75 degree column of 25 amps, so you can still put this on the 20 amp breaker, (cause #12 can not be on any breaker above 20 amps)

Having trouble locating it.

 

[480sparky]

310.15(B)(2)(a).

 

[brother]

310.15(B)(2)(a).

I read that part, but where does it actually say i can use the higher column (90 degree celsius )when derating, i know its in there somewhere, just can seem to locate it right now.

 

[480sparky]

You derate according to the insulation type. If it's a 90?C insulation, you start derating with the values in that column.

Edit to add: Specifically, the text is in the second column of Table 310.15(B)(2)(a).

 

[Chamuit]

Don't you use the column for the type of insulation you have? e.g. thhn 90 degree column

 

[misterbill1972]

Don't you use the column for the type of insulation you have? e.g. thhn 90 degree column

My past experiences have been upon what the city / AHJ will accept for the degree column to use.

 

[Chamuit]

My past experiences have been upon what the city / AHJ will accept for the degree column to use.

Hmm. Then they have superceded the NEC, which they can do.

 

[brother]

You derate according to the insulation type. If it's a 90?C insulation, you start derating with the values in that column.

Edit to add: Specifically, the text is in the second column of Table 310.15(B)(2)(a).

so it says, "Percent of values in tables 310.16 throurgh 310.19 as adjusted for ambient temperture if necessary"

This is the text in the second column of table 310.15(B)(2)(a), I just dont read it there. Am i missing something??

 

[Smart $]

Having trouble locating it.

See 110.14(A)(1)(a)(2) and (4), and 110.14(A)(1)(b)(2)

 

[brother]

See 110.14(A)(1)(a)(2) and (4), and 110.14(A)(1)(b)(2)

Thanks, I actually found it before you just put up your posts. The main one i was looking for was 110.14(C) temperture limitations.

 

[Smart $]

The main one i was looking for was 110.14(C) temperture limitations.

That's the one I meant, but a bit sleepy, I mistakenly typed in an (A) instead of (C)...

See 110.14(C)(1)(a)(2) and (4), and 110.14(C)(1)(b)(2).