1600A Service to MCC

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nhee

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An existing MCC w/1600A main is fed with 4 #500 per phase. Originally (site is 1970's vintage), the site motor loads (I assume) would have allowed the breaker to be sized per 430.63. Many of the original larger motor loads have since been removed, so that using 430.63 now gives an overcurrent device rating less than 1600A. Other electrical system upgrade work is now being performed on site. Would code now require either increasing service conductor size or a new breaker that does not exceed the ampacity of the existing conductors?
 
Re: 1600A Service to MCC

Are you talking about a main breaker in the MCC, or the breaker at the supply end of the 500KCM wires?

STeve
 
Re: 1600A Service to MCC

Based on drawings (I have not been to the site) the #500s feed a 1600A MCB within the MCC. A 1200 KVA (480/277 sec) utility transformer feeds the site.
 
Re: 1600A Service to MCC

Ron -

The 1600A MCB is the service disconnect/OCP for the site, based on the drawings I have. The 500's are the service conductors.
 
Re: 1600A Service to MCC

Article 430 can not be used to size service conductors.

My guess is that they went to the next size breaker above the 1520 A capacity of the 500KCM conductors, but that is only allowed for 800 amps or under.

I think the breaker setting should either be reduced like Ron suggested, or the conductors upsized. (Of course, Ron's solution is much cheaper if possible).
 
Re: 1600A Service to MCC

Agreed that Article 430 can't be used to size service conductors. But 230.90(A) Exception 1 would allow the overcurrent protection to be sized according to 430.63. Maybe they originally used this exception, if it existed back then.

Thanks for the input.
 
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