Transformer Secondary, Single Piece of Equipment

[Npstewart]

Have a step up 112.5 KW transformer 208-3 primary to 480-3 secondary. The transformer is only for one piece of medical equipment. The medical equipment is required to have a 100A OCPD. So right now we have a 100A fused disconnect protecting the secondary of the transformer, then that disconnect is feeding the 100A disconnect that powers the machine. Can I get rid of one of these or does anyone have a better suggestion on how to do this? It just seems redundant. Thanks.


PS. The Xfrmr is about 40 feet away from the machine

 

[kingpb]

Does your transformer happen to be a delta-delta? If so, 240.4(F) applies and none is required.

Otherwise, 240.21(C1) thru (C6) apply, and with it being more than 25ft (and I doubt outside) you need it at the transformer.

The question is, do you really need one at the machine itself? In which case I'd say probably not, unless something is dictating otherwise.

 

[augie47]

I agree, but caution that with the delta secondary 240.4(F) is not truely a "free ride". In order to omit the secondary disconnect you need to address the ratio as noted in that section.
Also, with an ungrounded secondary, 250.21(B) applies.

 

[Npstewart]

I was just looking at the equipment shop drawings and it looks like the OCPD is actually built into the machine . I think I will stick with the 100A fused disconnect for the 112.5 xfrmr right at the transformer secondary and feed the enclosed breaker. To answer your question though it is a 208Y primary.

Thanks for the advice, I did still learn a couple things.

 

[augie47]

Note that, in this situation, you don't want to connect to your XO on the primary and, unless you ground one phase of the secondary, you still need to address 250.21(B)