Derating question....

[Silent One]

I have a 60 amp sub panel from my main 200 amp panel in an unfinished basement. These were installed by the electrician when the house was built in 2001. The sub panel has a 34" long 2 1/2" protective sleeve up to the cavity between floor joists into which all the branch circuits enter and pass to the sub panel. There are 10 current carrying conductors (including neutrals - a total of 5 runs consisting of 12-2 and 12-3 nm-b) and there appears to have been no consideration for derating of the conductors. Should there have been? Will this affect running additional circuits through the same sleeve as the sub panel is only 1/2 full (provided the feed to the subpanel is not overloaded)?

 

[Stuart in MN]

Assuming you're in the US so your wiring needs to meet NEC requirements, there is a provision for installing multiple NM-B cables through a short conduit sleeve without derating issues, but I'm not sure of the maximum length for the sleeve - I was thinking it was 24", but a quick look around online indicates it may be longer.

Hopefully one of the other guys with more experience in residential work can provide a more definite answer.

 

[Silent One]

Thanks - yes, I am in the US. I also saw the 24" length restriction in the NEC but then also ran across arguments that derating did not apply to my particular instance as mine would be considered a sleeve and not a raceway.

 

[walrus]

Thanks - yes, I am in the US. I also saw the 24" length restriction in the NEC but then also ran across arguments that derating did not apply to my particular instance as mine would be considered a sleeve and not a raceway.

Not sure it matters if its a sleeve( i doubt their is a definition of a sleeve in the NEC) or a raceway. If its over 24 inches it must be derated according to NEC and I think thats true even if you wire tied the NM-b together with wire ties aka bundling.

 

[sberry]

I am all for code compliance but here is a place to use some sense with the intent. The N in 12/3 may not count as you may know but are these hot highly loaded circuits? You have already derated them likely, these are not all fully loaded above 20A and while the distance of this sleeve may be stretching it the concern from heating here is really moot. That's a big pipe and its short, no worry. You can only pull so much from a 60 anyway.

 

[Aceman]

You have to remember 310.15(A)2 Exception may apply.