I have a circuit with continuous current @ 216.9 A. 216.9 A x 1.25 = 271.125 A so fusing at 300 A. 90° C conductors, three phase 4 wire circuit so using 80% adjustment per Table 310.15(B)(3)(a). Looking at 300 MCM @ 320 A under 90° C rating. 320 x 0.8 = 256 A. So technically ok to use 300 A fuses per next size up rule 240.4(B).
The question is can one use the next size up rule for the 75° C terminals that are rated 285 A with 300 MCM? 285 A is still greater than 125% of the continuous current (217.125 A). 240.4(B) speaks more to conductors and doesn't mention terminals... wondering what others are doing.
Thanks!
The question is can one use the next size up rule for the 75° C terminals that are rated 285 A with 300 MCM? 285 A is still greater than 125% of the continuous current (217.125 A). 240.4(B) speaks more to conductors and doesn't mention terminals... wondering what others are doing.
Thanks!