I got a machine that requires a 3phase 480 V power supply in addition to a 277 single phase for control purpose. The nearst supply available is out of a motor control center that is supplied from a distant switchgear (supplied from a transformer). The transformer neutral is grounded through a grounding electrode in the substation yard, it is bonded to the grounding bus from which all the loads supplied out of the switchgear get their grounding conductor(including our MCC). This sytem based on article 250.184, B, is a single point grounded system. The question I got is:Can I use the grounding conductor drawn from teh MCC grounding bus as my neutral for the equipment that requires the 277 V after I install a new electrode? or I must install a new transformer to derive teh neutral from?
A question Regarding NEC Article 250
- Thread starter abusaleh
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kentirwin
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- Norfolk, VA
Re: A question Regarding NEC Article 250
I'm not sure if I fully understand what you have. Is the MCC a four wire board? Doesn't sound like it as you would merely pull a neutral to your machine in the run from the MCC. Even if the board is 4 wire it may be more economical to use a control transformer at the machine.
Control circuits from my experience are very small loads necessitating just a small control transformer. Also, 250.184 falls under Grounding of Systems and circuits - 1 kv - and OVER (High Votage).
I'm not sure if I fully understand what you have. Is the MCC a four wire board? Doesn't sound like it as you would merely pull a neutral to your machine in the run from the MCC. Even if the board is 4 wire it may be more economical to use a control transformer at the machine.
Control circuits from my experience are very small loads necessitating just a small control transformer. Also, 250.184 falls under Grounding of Systems and circuits - 1 kv - and OVER (High Votage). - Status