I'd imagine that the situation I am about to explain is code compliant. However, since I can make no sense of it myself, I am hoping somebody can explain it to me.
Print info:
110A breaker, feeding #3 Thhn conductors, feeding 80A fuses, feeding an elevator
The #3 in only good for 100A (75 deg. terminals). I realize that OCP is upsized beyond the ampacity of the wire it feeds all the time for motor loads. However, since 80 amp fuses are installed downstream, how can that be the case here? Is there ever going to be a time when a smaller, 100A breaker would prove problematic? Aren't the 80A fuses going to let go long before the breaker? More to the point, does the code allow the breaker to be "oversized" in this case? If motor loading is the engineer's reason behind requiring a 110A breaker, then how will the 80A fuses work? It seems to me that if the 80A fuses are sized correctly for their load then the breaker upstream should be sized for the conductor ampacity. Is a person allowed to have an infinite number of undersized feeders and fused disconnects in series even if the last disconnect is actually fused at less than the ampacity of the conductors?
This type of situation occurs throughout the project I am on right now and I have been told it is done all the time. I’m not sure if I have explained my position very well so let me know if you don’t understand.
