Grounding three phase step up transfomer

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qlr

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Hello to all,
I am new to the forum and thanks for having me. I have some concerns regarding grounding/bonding a transformer being used backwards. That is to say we are using a 240v delta to 208v wye transformer to go from 208v to 240v. I have fed the 208wye side as my primary with no neutral- just three ungrounded conductors. Normally I have connected a ufer, or some other GEC to xo and then to case of the transformer, and this is done on the secondary side. In the scenario we are using this transformer in there is no xo connection because it is the 240v delta side of the transformer. I bonded/tied the B phase to case ground and now I have equipment ground at my panel- at least on A & C phases. My main question is do I need to connect the case of the transformer to a grounding electrode ie: water pipe, rod, or other made electrode? I did some searches here on the forum but did not come up with anything related to using a transformer in this fashion. Any help would be greatly appreciated.
Thanks in advance!
 
Rules requiring a grounding electrode are the same whether it is a system with a neutral conductor or a system with a grounded phase. NEC just refers to the "grounded conductor" for those rules and it applies to whatever conductor of the system is grounded.

One other thing I will mention though is if you are on 2014 there was a change regarding reverse feeding such transformers - you can not reverse feed just any transformer it must be "provided that the installation is in accordance with the manufacturer?s instructions" this is found in 450.11(B).
 
Wouldn't the manufacturers "System Bond" on the secondary Y side (now primary) need to be removed also?

Can he operate the Delta side ungrounded with ground detectors?

If he did ground the B phase of the Delta, it would be a wild leg, right?
 
shortcircuit2 said:
Wouldn't the manufacturers "System Bond" on the secondary Y side (now primary) need to be removed also?

Can he operate the Delta side ungrounded with ground detectors?

If he did ground the B phase of the Delta, it would be a wild leg, right?
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What's a manufacturer's system bond, X0 to case? I have never seen a transformer with the X0 factory bonded.

If he corner grounded one side of the Delta it would not be a high leg since it's a 3 wire Delta, not a 4 wire Delta.
 
Thanks for the input!

Thanks for the input!

Really appreciate the quick responses.

kwired- The manufacturer assured me this transformer is made for this purpose. The two voltages (primary 240v and secondary 208v) are so close that their windings are the same size.

GoldDigger- I can run a GEC to the main water pipe- it is exposed for the entire length and the occupancy is commercial.

shortcircuit2- I don't believe the manufacturer installed a system bond on this transformer (on the secondary side or any where else). I am not familiar with ground detectors and will investigate them.

Thanks again for the help.
 
I am in agreement with all of the preceding posts other than having a question on this one:

GoldDigger said:
I believe that the case needs to be bonded to the existing building GES, not just a separate new electrode.
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I'm not saying that is incorrect as so many "grounding" issues change from cycle to cycle, but I would like a Code reference as I have found that.

I would add that it might pay you to investigate any requirements of the equipment you are supplying. Some equipment. especially equipped with drives, does not care for ungrounded or corner grounded systems.
Perhaps a 240/120 transformer would be in order ?
 
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augie47 said:
I am in agreement with all of the preceding posts other than having a question on this one:



I'm not saying that is incorrect as so many "grounding" issues change from cycle to cycle, but I would like a Code reference as I have found that.

I would add that it might pay you to investigate any requirements of the equipment you are supplying. Some equipment. especially equipped with drives, does not care for ungrounded or corner grounded systems.
Perhaps a 240/120 transformer would be in order ?
Click to expand...


Thanks augie47,

I am supplying power to three phase motors so don't believe I should have any problems with corner grounded system.
 
You probably already have the transformer but if not consider properly sized buck boost transformers for your load. They do not need to be sized for the full KVA of the load only for the change of voltage/current and will be much smaller then a transformer sized for total load, and that should equate to less cost.
 
kwired said:
You probably already have the transformer but if not consider properly sized buck boost transformers for your load. They do not need to be sized for the full KVA of the load only for the change of voltage/current and will be much smaller then a transformer sized for total load, and that should equate to less cost.
Click to expand...

Thanks for the input kwired. I am done with the job now and passed inspection, but that doesn't mean much here in in East Bay Area, CA. Many of the inspectors around here know less than I do about electrical, but I believe my installation is safe which is what means most to me. Thanks to all who chipped in with their advice.
 
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