powersupplyguy@netzero.ne
Member
- Location
- Warner, NH
Greetings,
I have selected a 6kVA 480v 3 phase transformer for my design. I am now trying to select primary fuses. Transformer manufacture tells me NEC requires 12Amp. Seems reasonable. I believe he is using 167% for a 6 kVA 480v 3 phase unit. Manufacturer claims inrush current to be 300A @0.01 second.
I am looking at time delay fuse that has some current limiting. I think I might be able to squeek by with a RK1 10 amp fuse. The Cooper Bussman Edison LESRK melting time curve suggests I can get over 1000 Amps for 0.01 second. Looks like 350 Amps for 0.10 second which would satisfy rule of thumb posted here a little while back 12x for 0.1 second under post called "transformer inrush" I believe.
I don't think I can coordinate a breaker, so I will use a disconnect to get the power off locally.
Plan Bravo is to use 3 NTC inrush limiters if I start popping fuses. I've used them before when designing charge circuits for drives and rarely have had any problems.
Do you think I am on the right track here?
Thank you.
regards,
Bob
I have selected a 6kVA 480v 3 phase transformer for my design. I am now trying to select primary fuses. Transformer manufacture tells me NEC requires 12Amp. Seems reasonable. I believe he is using 167% for a 6 kVA 480v 3 phase unit. Manufacturer claims inrush current to be 300A @0.01 second.
I am looking at time delay fuse that has some current limiting. I think I might be able to squeek by with a RK1 10 amp fuse. The Cooper Bussman Edison LESRK melting time curve suggests I can get over 1000 Amps for 0.01 second. Looks like 350 Amps for 0.10 second which would satisfy rule of thumb posted here a little while back 12x for 0.1 second under post called "transformer inrush" I believe.
I don't think I can coordinate a breaker, so I will use a disconnect to get the power off locally.
Plan Bravo is to use 3 NTC inrush limiters if I start popping fuses. I've used them before when designing charge circuits for drives and rarely have had any problems.
Do you think I am on the right track here?
Thank you.
regards,
Bob