25kv delta/480v wye trans

[TWCCElec]

At our coal mine, we use 25kv/480v trans for our dewatering fields. When recently wiring up a new panel attached to the secondary on said transformer, my boss told me to wire from the secondary tap to the 400A main with parallel 2/0. Coming from construction, I know 2/0 is only good for 200A on residential service entrances. I don't feel comfortable doing this because, 1) I don't feel the paralleled wire sizes are big enough, 2) to do this it must be double lugged to back feed said breaker, 3) he also told me to grnd with just a number 2, which I know is nowhere near the circular mills required to feed a proper 400A service. Anyone got any opinions, code references to help me out?

 

[alehman]

Your boss needs some help. It's time to hire a competent engineer. Take a look at NEC tables 310.16 and observe required derating factors, and table 250.122.

I'm not sure where the panel is with respect to the source, but the feeder must have proper overcurrent protection at the source or must be installed per appropriate tap rules.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[TWCCElec]

He said something about the secondary tap of a trans you could drop wire size by 10%, which didn't make much since to me considering that wire from the tap to the main brkr is technically nothing more than a fuse link. Thanks for the nec references, that's just what I needed.

 

[waross]

He said something about the secondary tap of a trans you could drop wire size by 10%,

He may have misunderstood something that he didn't didn't hear properly in the first place.
There was a rule that mentioned taps and 10%. That was back in the 1972 edition of the CEC. That rule does not apply and has been repealed.

Bill
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"Why not the best?"
Jimmy Carter