I know how to calculate feeders and breaker/fuse size for motors. I think I have done a poor job of explaining my misunderstanding. First of all, I am not hooking up a motor; I am hooking up a listed unit. Thus, I would assume I would follow the nameplate and/or instructions. I would expect those items to state a maximum OCP and a minimum circuit ampacity. I searched briefly and could find no such information. I simply followed the engineered drawings and now I am trying to understand them. The disconnect inside the elevator mechanical room has 80A fuses. I feed those 80A fuses with #3 Cu THHN. Those threes terminate in a 110A breaker. My question is: why can the threes be sized for motor load when fuses sized 30A less are installed downstream? Do you think the company that manufactures the elevator requires this set-up? It seems to me that the conductors from the fused disconnect to the elevator equipment could be sized based on the rules established for motors. However, any conductor before that should meet the requirements of 310.16 should it not? Also, I realize that fuses and breakers do not react the same. If a conductor-sized, 100A breaker were used (in place of the current 110) what type of circumstance would cause it to trip before 80A, time-delay fuses? Thanks
