Conductor Temperature Rating
Definition
The maximum continuous operating temperature of a conductor's insulation, typically 60°C, 75°C, or 90°C. Higher ratings allow more current, but terminations (breakers, outlets) often limit usable ampacity to 75°C values.
Practical Note
THHN is rated 90°C but typically used at 75°C ampacity due to termination limits. NM-B (Romex) is 60°C rated. Higher ambient temperatures reduce the allowable conductor temperature rise.
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