I am trying to figure out how this would work.
You have an outside step down transformer. 4160 primary Delta, 460 Delta secondary, pad mount, 75KVA They want to feed out of the secondary lugs of this transformer, go a ways, and then fed another transformer, 480 delta primary,3 wire ,208/120 wye secondary, 75KVA, pad mount. We are debating about the OCPD?s that are needed and where they would be at. One of the guys says you don?t need OCPD protection at all. My thought is that you need OCPD in accordance with 450.3B and then go to the table, 450.3(B). I say we need a fused disconnect before the 2nd transformer and fuse it at 125% of the load. Also, it is ringing a bell, that if you have a 4 wire secondary, you need over current protection for the secondary side. Your overcurrent protection won?t see your phase to neutral loads correctly and will overload. I don?t work with transformers much, so I am digging around. However, the 2nd transformer needs to be protected.
You have an outside step down transformer. 4160 primary Delta, 460 Delta secondary, pad mount, 75KVA They want to feed out of the secondary lugs of this transformer, go a ways, and then fed another transformer, 480 delta primary,3 wire ,208/120 wye secondary, 75KVA, pad mount. We are debating about the OCPD?s that are needed and where they would be at. One of the guys says you don?t need OCPD protection at all. My thought is that you need OCPD in accordance with 450.3B and then go to the table, 450.3(B). I say we need a fused disconnect before the 2nd transformer and fuse it at 125% of the load. Also, it is ringing a bell, that if you have a 4 wire secondary, you need over current protection for the secondary side. Your overcurrent protection won?t see your phase to neutral loads correctly and will overload. I don?t work with transformers much, so I am digging around. However, the 2nd transformer needs to be protected.