back feed 30-KVA transformer

[LEADFOOT2]

I have a Sq-D EX30T3H transformer, have a situation that the customer wants to supply the xmer on the secondary with 120 / 208V, to produce 480V on the primary. Are there any pitfalls in doing such ?

The transformer is designed for 480V, delta primary... 120 / 208V WYE secondary.

 

[texie]

I have a Sq-D EX30T3H transformer, have a situation that the customer wants to supply the xmer on the secondary with 120 / 208V, to produce 480V on the primary. Are there any pitfalls in doing such ?

The transformer is designed for 480V, delta primary... 120 / 208V WYE secondary.

Yep, a whole bunch of reasons not to do this. You will have a delta 480 output which in almost all cases is a negative and for some loads is a deal breaker. The correct 208 delta to 480Y transformer is readily available and is a much better choice.

 

[LarryFine]

Are there any pitfalls in doing such ?

The transformer is designed for 480V, delta primary... 120 / 208V WYE secondary.

One caveat: If you do connect a Y secondary as a primary, do not connect the supply neutral to X-0; let it float as if it was a delta primary.

As stated above, your new delta will require corner-grounding, neutral derivation, or ground detection.

The delta-Y transformer Tex mentioned is better, unless you need an ungrounded delta for some reason.

 

[augie47]

If you are under the '17 Code, see 450.11(B). You can only backfeed a transformer provided you have manufacturer's instructions.
There was a recent thread that went into detail as to why but I can't seem to locate it.

 

[infinity]

I've noticed that on many new transformers the nameplate specifically says something like "for step up use only".

 

[norcal]

Another thing to add to the reasons above not to do it, See 450.11(B) this can nix doing a backfed X-former.

 

[LEADFOOT2]

back feed transformer

back feed transformer

Other info that I didn't add was that the owner wanted to use the same transformer as a step up & step down via of xfer switches. As I read the replies ( which joggled my brain cells ) & the deeper I thought about this scenario, it's not going to work. So, I have to come up with another plan.

Thanks all for your inputs.