Delta panel fed from Wye Transformer

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drmoody

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I am setting up a service for a US company that bought some equipment from a plant in Canada. All of the equipment is 575V 3-phase. Believe it or not, the POCO has a 347/575 transformer on hand. My MDP is 370 feet away and I don?t want to install a neutral conductor due to budget constraints and the fact that it should never be needed.

Questions:
What do I do with the XO tap on the secondary side of the POCO?s transformer...if anything?
Do I install an EGC and if so, to what does it connect?
 
drmoody said:
Questions:
What do I do with the XO tap on the secondary side of the POCO?s transformer...if anything?
Click to expand...

It has to be brought as far as the service disconnect


Do I install an EGC and if so, to what does it connect?
Click to expand...


Yes and at the service disconnect.

You have to treat this as a Wye service, once you get past the service disconnect you can bring your delta feeder from there to the equipment.
 
I was thinking about this exact thing just the other day (not the voltage, but the need for the grounded conductor to the service disconnect.)

My take is from 250.24(C).

If the POCO does not connect the X0 terminal to ground, then the "neutral" does not need to be brought to the service. It would essentially be an ungrounded service with no need for the fourth wire.

Did I miss something?
 
crossman said:
If the POCO does not connect the X0 terminal to ground, then the "neutral" does not need to be brought to the service.
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It is my impression that the POCO will bond XO.

But it certainly seems worth asking them about.
 
Thinking on this more I think that with a pad mount the utility has no choice but to bond XO to protect the public from a secondary winding to case fault.

But I certainly could be mistaken.
 
For safety's sake, I agree that the POCO should ground the X0 and that the neutral should be brought to the service with all the proper grounding, MBJ, all that stuff. Most likely they would.
 
IF the serving electric utility is willing to provide an ungrounded service AND the X0 is not internally case grounded (not likely but the schematic on the nameplate will show it if it is connected), this may be done. In fact, this could actually be done as a corner grounded delta if they grounded a phase. :smile:
 
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