If a circuit breaker has lugs rated at 90 deg. C, can 90 deg. C wire be used at the 90 deg. C ampacity?
Legacy and Powerpact circuit breakers
Lug temperature rating is widely misunderstood and can easily result in misapplication of the incorrect conductor size.
When terminations are inside equipment such as panelboards, motor control centers, switchboards, enclosed circuit breakers, safety switches, etc., follow the temperature rating identified on the equipment labeling instead of the rating of the lug itself. Manufacturers commonly use 90 °C-rated lugs (i.e., marked AL9CU) on equipment rated only 60 °C or 75 °C. The use of the 90 °C-rated lug in this type of equipment does not allow the installer to use 90 °C wire at the 90 °C ampacity.
The Underwriters Laboratories® General Information on Electrical Equipment Directory states the following about terminations:
“A 75 °C or 90 °C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that a 75 °C or 90 °C insulated wire can be used unless the equipment in which the terminals are installed is marked for 75 °C or 90 °C.” Review the labeling of all devices and equipment for installation guidelines and restrictions.