[Clutchcargo]

I'm wiring a pair of light switches using 12/2 NM in a metal stud wall around a chimney. So 1 wire in and 2 wires following that wire back around the chimney to a switched receptacle and ceiling fan.
With that said, I drilled 7/8" holes and added bushings to the metal studs. There is enough room for 3-12/2 cables without pinching the wire. Would the bundling of 3-12/2 cables for 5 feet need to be de-rated below 20AMPs?

 

[Arrow3030]

Is there thermal insulation? The adjustment is 80% of the allowable ampacity. De-rating is a term not used much anymore.

 

[Clutchcargo]

No, there is no thermal insulation. So is that 80% of 20 amps?

 

[Arrow3030]

It would be 80% of 30A

 

[Clutchcargo]

Perfect, thanks.