Feeder Size

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Alwayslearningelec

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So one normal feed and one EM to the same ATS just about same distance each.
The normal feed has an shunt trip breaker in the run.
The engineer calls for (3) sets of 500's for the normal feed but only (2) sets of 600's for the EM feed. Not sure why different, should be the same right?
Even so the (2) of 600's aren't enough as the fuse size is 1000A.
 

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horsegoer said:
So one normal feed and one EM to the same ATS just about same distance each.
The normal feed has an shunt trip breaker in the run.
The engineer calls for (3) sets of 500's for the normal feed but only (2) sets of 600's for the EM feed. Not sure why different, should be the same right?
Even so the (2) of 600's aren't enough as the fuse size is 1000A.
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I’ve actually seen smaller size EM feeders done before. It seems counterintuitive but load reduction via load shedding might be part of the design. Also, make sure you use the design ampacity as stated in the project drawings and not necessary the NEC table ampacity. There might be adjustment/correction factors applied or calculated ampacity as determined under engineering supervision. This may allow 2 sets of 600’s to be protected by a 1000A OCPD.
 
We have had designs where elevator EM switchboards were fed with fewer sets of EM feeders because not all of the cars were designed to run at once when on EM power.
 
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