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Sprayed Foam Attic #2


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In the garage area of this attic, the electrical cables got coated with sprayed polyurethane foam. It is not uncommon for attic temperatures here to reach over 140 degrees in the summer time. Is it safe to assume that all these cables should now be derated or how would you go about fixing the problem?


Jeff Euriech

Peoria Arizona

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How would this be any different from any other garage attic in your area?

Those are modern romex cables with 90-degree conductors inside, and it's unlikely that the amibient temperature down low in the attic in that picture gets much above 140 degrees. So to apply that derating, you'd take 71% of the 90-degree ampacity for those wires. That would yield an ampacity that's still well above the orginal ampacity for the romex cable assemblies.

So derating for temperature, in this case, wouldn't have any effect on the installation.

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