ROMEX adjustment factors

[fredspence1]

334.80 starts with "The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15." 310.15 B(2) says "...multiconductor cables are installed without maintaining spacing for a continuing length longer than 24 inches...(2008 NEC)," and exception # 3 still says "Derating factors shall not apply to conductors in nipples having a length not exceeding 24 inches." This seems to indicate that adjustment factors should NOT be applied to ROMEX placed in notches or bored holes if the bundling does not exceed 24 inches. However, the last paragraph of 334.80 (2008 NEC) leads one to believe that any strand of ROMEX exposed to thermal insulation must be adjusted regardless of length. It appears that Code Panel 7's intent was to apply the adjustment factors for any length because they felt the proximity issue could exceed the allowable temperature rating even at length less than 24 inches. So, the question is: Do we adjust ROMEX for nipples less than 24 inches if it is installed through bored holes or notches filled with thermal insulation?

 

[barbeer]

I would love to see someone install cable in a conduit nipple and fill it with insul..

I believe the intent of 334.80 is to have cable only and not a nipple.

But answering your question specifically- yes.:smile:

 

[Dennis Alwon]

334.80 is talking about draft stop not regular insulation. That usually means through bored holes between floor where they fill the hole with the foam etc.