ezdrocks
Member
- Location
- Houston, Texas, USA
- Occupation
- I&E Designer, Industrial Electrical and Instrumentation design (NOT an engineer but close)
I've searched online but am having a hard time with this one.
I have a 7,500kva, 12,470x4,160 transformer that I need to feed to two separate locations.
Originally, the secondary was to feed a set of MV MCC gear inside an MCC building. This gear was going to have a breaker to feed out to a 1500kva 4,160x480 transformer. However, the company that specified the MCC gear, did not put in this breaker, and didn't leave room in the building to add one. So now I am trying to figure out how to feed a) The original incoming main on the 4,160 MV MCC Switchgear, and b) The primary side of the 4,160x480 transformer, from the secondary of the first transformer.
I would like to feed both directly off the secondary side of the 12,470x4,160 transformer, but I need to protect the incoming primary on the smaller transformer. I was going to put something like a Square D Mini-Break with a 250A Fused disconnect in line between the first and secondary transformer, but NEC 240.21(C)(3)(3) says "All overcurrent devices are grouped".
The transformers would be next to each-other, and the incoming main inside the MCC building would be within the 25' length, but the overcurrent devices are not grouped.
I looked at 240.21(C)(4) "Outside secondary Conductors", and this seems like a viable option, except I'm questioning point (2), "The conductors terminate at a single circuit breaker of a single set of fuses...". Is this statement saying that there can only be one fuse (or other OCPD) total, or for each set of conductors leaving the transformer secondary?
Thanks for your help.
I have a 7,500kva, 12,470x4,160 transformer that I need to feed to two separate locations.
Originally, the secondary was to feed a set of MV MCC gear inside an MCC building. This gear was going to have a breaker to feed out to a 1500kva 4,160x480 transformer. However, the company that specified the MCC gear, did not put in this breaker, and didn't leave room in the building to add one. So now I am trying to figure out how to feed a) The original incoming main on the 4,160 MV MCC Switchgear, and b) The primary side of the 4,160x480 transformer, from the secondary of the first transformer.
I would like to feed both directly off the secondary side of the 12,470x4,160 transformer, but I need to protect the incoming primary on the smaller transformer. I was going to put something like a Square D Mini-Break with a 250A Fused disconnect in line between the first and secondary transformer, but NEC 240.21(C)(3)(3) says "All overcurrent devices are grouped".
The transformers would be next to each-other, and the incoming main inside the MCC building would be within the 25' length, but the overcurrent devices are not grouped.
I looked at 240.21(C)(4) "Outside secondary Conductors", and this seems like a viable option, except I'm questioning point (2), "The conductors terminate at a single circuit breaker of a single set of fuses...". Is this statement saying that there can only be one fuse (or other OCPD) total, or for each set of conductors leaving the transformer secondary?
Thanks for your help.