Hello,
Can a 75 degree C rated circuit breaker be installed with a 60 degree C insulation wire if the 60 degree wire is oversized for this application? Or we must use 75 degree C wire since it is marked this way on a circuit breaker?
Thanks for everyone's input.
Good question.
This is only the case when your circuit breaker is dual-rated for 60C/75C. This means you could use either
A. 60C sizing and 60C wire
B. 60C sizing and 75C wire
C. 75C sizing and 75C wire
D. 75C sizing and 90C+ wire
If your circuit breaker is straight rated for 75C, without carrying a dual 60C rating, your options are:
A. 60C sizing and 75C wire
B. 75C sizing and 75C Wire
C. 75C sizing and 90C+ wire
If your circuit breaker is straight rated for 60C, or if it doesn't carry any specific rating while being 100A and less, your options are as follows. Note that this is rare with modern equipment.
A. 60C sizing and 60C wire
B. 60C sizing and 75C wire
C. 60C sizing and 90C+ wire
In rare cases, you can use 90C termination sizing and 90C wire. Most if not all, manufactured equipment is limited to 75C in some form or another. Field-installed connectors (Polaris insulated tap blocks, insulation piercing connectors, split bolts) commonly are 90C, and if you install them in an enclosure separate from equipment, with a short segment of 90C wiring with 75C sizing, you can take advantage of the 90C rating for the main run. One reason you might do this, is if you screw up by forgetting to use 75C termination sizing, and need to remediate the situation. Another reason is that it could be a value-engineering decision.
This is explained in the following white paper:
http://www2.schneider-electric.com/...7/en_US/Wire Terminations 0110DB9901R2-02.pdf