Conductor temperature of terminations

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Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
I know that generally in accordance with the UL white book that 0-100 amps the wire termination temperature is assumed to be 60 deg C & 100 amps and up it is assumed to be 75 deg C If the equipment is not marked.

At least in my area service entrance conductors are usually sized at 75 C. When replacing an existing panel some or all of the older wiring (branch circuit & feeders) is 60 C wire.

I heard somewhere, that to use 75 C terminations and size the service entrance at 75C then all wiring in the panel (branch circuits & feeders, breakers etc.) must be rated 75 C. Is this true?? I don't see how it could be.

I have looked in the NEC and in my old "McGraw Hill handbook of electrical construction calculations" and haven't found a clear answer.

Thanks for the help!

Eddie 702
 
Eddie702 said:
I heard somewhere, that to use 75 C terminations and size the service entrance at 75C then all wiring in the panel (branch circuits & feeders, breakers etc.) must be rated 75 C. Is this true??
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Don't believe everything you hear. This is not true. The ampacity of any given conductor depends only on its cross sectional area, its terminations, and its "conditions of use." For example, a wire might have to be given a lower ampacity if it is run in the same conduit as too many others. But the ampacity of a conductor is not constrained by the ampacity of anything downstream.

The other two references you named are all well and good. But the primary reference you should use is the NEC itself. I suggest starting at 110.14(C)(1)(a)(3).

Welcome to the forum.
 
I agree with Charlie another electrical myth. In many cases the wiring in a home is all rated for 60° C unless it's modern SE, AC, or MC cable.
 
infinity said:
I agree with Charlie another electrical myth. In many cases the wiring in a home is all rated for 60° C unless it's modern SE, AC, or MC cable.
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Or is fixture wire supplied as part of a light or fan, etc.

Note: So slow (35 seconds!!!) that it auto-saved while working on the Post.....
 
charlie b said:
Don't believe everything you hear. This is not true. The ampacity of any given conductor depends only on its cross sectional area, its terminations, and its "conditions of use." For example, a wire might have to be given a lower ampacity if it is run in the same conduit as too many others. But the ampacity of a conductor is not constrained by the ampacity of anything downstream.

The other two references you named are all well and good. But the primary reference you should use is the NEC itself. I suggest starting at 110.14(C)(1)(a)(3).

Welcome to the forum.
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Thank you. Glad to be here.
 
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