Is romex inside conduit derated?
NM cable used inside conduit is uncommon and most inspectors will push back, but yes — wherever conductors share a raceway, NEC 310.15(C)(1) ambient + adjustment factors apply, and NM is still capped at the 60°C column per 334.80. The combined effect is usually worse than just pulling THHN/THWN in conduit and sizing from the 75°C column. If you actually need NM-through-conduit (a short sleeve through a wall is the common case), the short raceway exception in 310.15(C)(1) waives the bundling derate.
Answers
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