Hello everyone this is my first post:
I was recently taking a review class at our training center, using the MIke Holts electrical exam preparation book. In there I saw an Illustration, 11-4 unit 11 commercial load calculations. What it illustrates is fusing a disconnect for an AC unit with a minimum circuit ampacity of 23 amps and a maximum fuse size of 40 amps. Ultimately it is fused at 40 amps (225%)in this illustration #12THHN wire is used, but somewhere down the line there is a panel for sure where the number 12 THHN is protected by a 20 amp Circuit breaker.
Maybe because I am not a big student of fuses and all their characteristics, but I cannot see the sense in this because the 20 amp breaker will, in my understanding will always over ride the 40 amp fuses. so why even bother fusing that high?
I was recently taking a review class at our training center, using the MIke Holts electrical exam preparation book. In there I saw an Illustration, 11-4 unit 11 commercial load calculations. What it illustrates is fusing a disconnect for an AC unit with a minimum circuit ampacity of 23 amps and a maximum fuse size of 40 amps. Ultimately it is fused at 40 amps (225%)in this illustration #12THHN wire is used, but somewhere down the line there is a panel for sure where the number 12 THHN is protected by a 20 amp Circuit breaker.
Maybe because I am not a big student of fuses and all their characteristics, but I cannot see the sense in this because the 20 amp breaker will, in my understanding will always over ride the 40 amp fuses. so why even bother fusing that high?
