generator feeder

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jbolen

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I have 175 KVA genrator 120/208 3 phase.....There is a 400 amp bkr on genrator.
We are feeding a 225AMP main circuit board panel

Question.....What size wire to the 225 amp main
 
Unless the feeder to the 225 amp OCPD meets one of the tap rules in 240.21(B) you will need cable with an ampacity of 400 amps.
 
You would have to size the conductors by the overcurrent device protecting them. 400 amp UNLESS you can qualify for one of the tap rules
in 240. Look at 240.21(C)(5) and see if your install meets those parameters.

sorry Don, stepped on you (slow typing this morning) ..but same advice
 
jbolen said:
I have 175 KVA genrator 120/208 3 phase.....There is a 400 amp bkr on genrator.
We are feeding a 225AMP main circuit board panel

Question.....What size wire to the 225 amp main
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As don and gus said, of course - except I think gus meant 240.21.B.5.

Your CB is an odd size for your gen. Maybe it is aftermarket, add-on, or separately provided. If so, if the 225A panel board is the only load, an option is to change the cb trip unit to 225A and use 225A conductors.

That amswered your question, so now my question: Why the odd gen CB size?

I'm surprised the Gen CB is only 400A. 208V, 3ph, 175kva, .8pf is 607A. Conductors from the gen to the first OCP are required to be 115%, which is 698A. I would have expected a 700A or 800A cb for a package installation. So I'm wondering, how come the CB on the gen is 400A ?

cf
 
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