Feed thru Lugs to Supply Step-Down Transformer

[Npstewart]

Im working on a shell warehouse building where a lot of the equipment may end up being 208v in certain areas so the transformer may end up handling the entire load. The incoming voltage is 480/3.

For a 150 kVA transformer, would it be permissible to feed a 480v panel from the MDP, then use feed thru lugs to feed the transformer right from the lugs within the panel provided the conductors were the same size from the MDP, thru the panel, to the transformer primary? Or, would I need to use a 200A sub-feed breaker within the 200A panel?

Normally I would provided primary protection for the xfrmr within the 480v panel but because the entire load may be 208v, im having an issue with this.

Thanks

 

[beanland]

One OCPD, two loads

One OCPD, two loads

This could get tricky. A 150kVA is 180AFL. You could use a 400A breaker to protect the primary on the transformer and 500A breaker on the 208V. But, that same 400A breaker has to be rated for the panel bus and feeder. Seems you could use a 400A panel and 400A feeder. The panel, feeder and transformer are all protected to NEC. Seems all reasonable. I welcome debate and clarification from others with more experience.

 

[Npstewart]

I think im going to go with the sub-feed breaker kit for the panels. The 400A panel would work but I think it may be more expensive in the end.

 

[charlie b]

Good choice. If I correctly understood your initial description, I think it would have violated 240.21(C)(2)(2).

 

[Npstewart]

Thank You both. Have a great weekend!