Time- delay fuses and Motor Load Calculations
Time- delay fuses and Motor Load Calculations
(OP)
We Recently have a disagremment with the enginers of Ingersoll-Rand when in a installation of a new compressor, our calculations take place for a 25 HP/3ph/208 V Design B Motor; need Time-Delay Fuses of 70 A and #4 THHN AWG Copper Conductor to feed this compresor; when they came with #6 AWG size conductors. What do you think about it?





RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
Did you take into the account of allowable voltage drop and other derating factors when you reach your cable sizing?
It is difficult to comment who is correct as information given is limited. What is the cable length and cable installation method?
RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
If your fuse ratings are larger than the capacity of your conductors, then the fuses won't be able to protect your conductors.
RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
RE: Time- delay fuses and Motor Load Calculations
If this is a "package system" with motor starter and controls provided by I-R then you will have to use whatever overcurrent protection they have obtained their UL listing based on. This is a common "feature" of HVAC equipment where the UL listing is based on the use of an upstream fuse. In these cases, a fuse MUST be used to meet NEC/UL requirements, regardless of any technical issues. There are thousands of HVAC packages fed from a circuit breaker in a switchboard that also have a *fused* disconnect at the equipment.