Derating of electrical wiring due to house insulation
I am rewiring my home both to upgrade the service and to bring up to current code. After I rewire, I will be fully insulating the house with foam insulation in the exterior walls and around duct work, 18 inches of dense pack insulation in the attic area, and if possible 1" thick vacuum insulated foam behind electrical boxes on exterior walls (2x4 construction so may not have room behind the boxes).
This will result in the wiring not being able to efficiently cool by transfer heat from the wires. I will mostly be using 12-2 and 12-3 (20 amp circuits) romex with one circuit using 10-2 (30 amp circuit).
Should I de-rate the wiring? If so, how much? Should I use 10-2 and 10-3 even though they will be on 20 amp circuits, and the 8-2 for the one 30 amp circuit?
I expect to have no wall wires running in bundles. I will have to be more careful above the ceiling, but that should more be remembering not to let the wires be too close than any other problem.