In NEC ampacity calculations, what temperature rating is assumed if the insulation temperature rating is not specified?

In NEC ampacity calculations, what temperature rating is assumed if the insulation temperature rating is not specified?

• A. 60°C
• B. 75°C
• C. 90°C
• D. 105°C

Answer: (A)

Ampacity depends on the insulation’s temperature rating because that rating tells you which column of the ampacity tables to use. If the insulation temperature rating isn’t specified, the NEC uses 60°C as the default. This conservative assumption keeps the calculated current within what most insulation and terminations can safely handle when the rating isn’t known. You may use a higher rating (75°C or 90°C) only if the insulation is actually rated for that temperature and the installation and terminations support it.

Ampacity depends on the insulation’s temperature rating because that rating tells you which column of the ampacity tables to use. If the insulation temperature rating isn’t specified, the NEC uses 60°C as the default. This conservative assumption keeps the calculated current within what most insulation and terminations can safely handle when the rating isn’t known. You may use a higher rating (75°C or 90°C) only if the insulation is actually rated for that temperature and the installation and terminations support it.