Derating wire

[TiredDude]

I am aware that there is the need to derate the ampacity of wire for ambient temperature (say an attic in the midwest, 120*F-130*F?) and also derating for other situations, such as bundled wire.

If a wire is bundled in an attic, I understand that both bundling and ambient temp derating factors should apply cumulatively. Makes sense.

What about a wire that is bundled in the basement near the service panel, that is later unbundled and travels through the attic? Common sense says derate the wire for the local condition, i.e. derate for bundled, derate for attic temp, and apply the largest derate factor of the two to the whole wire.

I have read some statements on another site indicating that you would apply both derating factors to the wire on a cumulative basis, even if the derating conditions are in separate areas.

Any electricians/code experts that can clarify this?

Thanks.

 

[sberry]

How long is the bundle in the basement and how much you figure realistically is ran at the same time? Are there hi current carrying circuits in the attic?

 

[JoeFin]

If by "Bundling" you mean the upper section of the panel where they pass through to the top plate of the wall framing .... then No

You do not have to derate ampacity for ******* of 24" or less

 

[TiredDude]

Assume a derating factor is necessary for bundling. And assume that a derating factor is needed for attic heat.

Would they both have to be applied even if the bundling is in the basement? It is more a of theoretical question than an actual example.

 

[Charles (in GA)]

If the bundling is in a cool area, and the wires in the hot area are not bundled, then figure the derating for each, and pick the highest derate and use that, but NOT both of them added together.

As already noted, short runs do not count in bundling.

Charles

 

[TiredDude]

If the bundling is in a cool area, and the wires in the hot area are not bundled, then figure the derating for each, and pick the highest derate and use that, but NOT both of them added together.

As already noted, short runs do not count in bundling.

Charles

Yeah, that makes sense to me, but I am being told elsewhere, that both factors have to be applied (cumulative derate).

Is there any code guidance on the specific situation? I also asked the other guy for a code reference.