Code Q&A: Adjusting Ampacity of NM Cable

Code Q&A: Adjusting Ampacity of NM Cable

NEC rules for adjusting the ampacity of an NM cable

Q. When walls are insulated by filling them with spray-applied polyurethane foam insulation — or other types of insulation — must the ampacity of Type NM cable in that wall be adjusted?

Find the Answer

A. Where more than two NM cables are installed in contact with thermal insulation without maintaining spacing between cables, the allowable ampacity of each conductor must be adjusted in accordance with Table 31

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