feeding two transformers by one circuit breaker

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123rashab

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project manager
I have this installation where we cannot shutdown the maingear or do any changes to existing wirings.

the client wants to install two 75kva delta-Y 480v-208v transformers. the existing gear has (1) 225A (#2/0 conductors) CB and (1) 200A CB (#250MCM conductors) that are spares/unused.

1. can I use one of the two CBs to feed the two 75kva transformers?
2. if I must use both CBs for this installation, how can i work around not being able to change the CBs/Wire sizes. i.e, if we decide to use the 225A (#2/0 conductors) CB, can I run those to a 175A fused disconnect then continue with the installation as normal?
and, if i use the 200A CB (250MCM) shall I run the wires into a 125A fused disconnect and then reduce the wire size based on the disconnect rating then continue with the installation normally?

thanks!!
 
If you will also provide secondary protection per Table 450.3(B), then you are permitted to make the primary protection up to 250% of FLA, so 225A breaker would be ok with 225A wire. You may have to be creative for startup and/or an outage/restart because the inrush may trip the 225A breaker.
 
Is this equipment fed by an uninterruptible power source? If not, it can be shut down as happens every time there is a utility outage.

But yes, one feeder breaker can be used to feed multiple transformers. Your option #2 makes sense.
 
ron said:
If you will also provide secondary protection per Table 450.3(B), then you are permitted to make the primary protection up to 250% of FLA, so 225A breaker would be ok with 225A wire. You may have to be creative for startup and/or an outage/restart because the inrush may trip the 225A breaker.
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understood. but the 225A breaker has #2/0 wires which are rated up to 175A only at 75deg.
that is where my dilemma lies. cant cahnge the breakers or the wires and have to use what is avaiable to me as above.
 
jim dungar said:
Is this equipment fed by an uninterruptible power source? If not, it can be shut down as happens every time there is a utility outage.

But yes, one feeder breaker can be used to feed multiple transformers. Your option #2 makes sense.
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shutdown IS possible, however the client refuses to do so.

how can i use one breaker to feed two transformers? run the feed into two separate 100/125A disconnects and then to the transformers?
 
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