Volta
Senior Member
- Location
- Columbus, Ohio
A customer has an occasional problem. In a MCC, a 5kva, single phase, 480:120 transformer sometimes trips a 2 pole 20 amp din rail mounted breaker.
Secondary load is a resistive (oil) heater, 12 amps. Primary reads 3 amps or so when it holds (usually).
I assume this is an inrush issue. What are suggested ways to overcome this problem?
I see in a good post from templdl in 2007 that the smaller transformers can allow a greater percentage of inrush current. Can a time delay fuse handle this where an (inverse time?) breaker doesn't? I am ok with the manufacturer protecting the x-former with a (primary only) 20 breaker, but it wouldn't meet 450.3(B) if I did it.
Any ideas?
Secondary load is a resistive (oil) heater, 12 amps. Primary reads 3 amps or so when it holds (usually).
I assume this is an inrush issue. What are suggested ways to overcome this problem?
I see in a good post from templdl in 2007 that the smaller transformers can allow a greater percentage of inrush current. Can a time delay fuse handle this where an (inverse time?) breaker doesn't? I am ok with the manufacturer protecting the x-former with a (primary only) 20 breaker, but it wouldn't meet 450.3(B) if I did it.
Any ideas?