# Grounding transformer 208 to 480



## RePhase277 (Feb 5, 2008)

The way it is now, the delta side has no equipment grounding path. Personally, I'd ground one of the phases of the delta. This is called a "corner grounded delta". The grounded phase has to be identified white just like a neutral. And like a neutral, you can't put a fuse in line with it. Circuit breakers are OK if all the phases open simultaneously.

The other compliant but more difficult and costly options are to use fault indicators or a zig zag grounding transformer.


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## eddy current (Feb 28, 2009)

Can u not ground the secondary and install ground fault indicating lights? Like an old ungrounded service.


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## RePhase277 (Feb 5, 2008)

eddy current said:


> Can u not ground the secondary and install ground fault indicating lights? Like an old ungrounded service.



Why install the indicators if it is grounded?


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## eddy current (Feb 28, 2009)

InPhase277 said:


> Why install the indicators if it is grounded?


Sorry,
Don't ground the secondary and install the indicating lights is what I was trying to say.


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## WEGI (Dec 27, 2015)

Thanks for all the advise,
Would the indicator lights still meet the intent of the code there are no full time electricians on the site. and would it still be safe.
I am trying to make my mind up about having to eating the cost and replacing the 6 x 45 KVA transformers for the delta wye 208 480. (Unfortunately I allowed myself to listen to the supply house (Which is all my fault) when purchasing these instead of doing my own due diligence first. Like they say you can't buy experience but in most cases you can get charged for the lack of it.)
I'm not sure if I can do the corner ground delta as it becomes a grounded conductor as the compressors are required by the manufacturer to have a fused disconnect with 100 amp JKS fuses in front of them. This seems to be problematic as it appears that the grounded corner conductor can not be fused.
I am open to any ideas anyone may have. Especially if it costs less than replacing said transformers. (I am naturally tight to begin with, but I also need to do the right thing by my customer and his employees)
Thanks again


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## RePhase277 (Feb 5, 2008)

WEGI said:


> Thanks for all the advise,
> Would the indicator lights still meet the intent of the code there are no full time electricians on the site. and would it still be safe.
> I am trying to make my mind up about having to eating the cost and replacing the 6 x 45 KVA transformers for the delta wye 208 480. (Unfortunately I allowed myself to listen to the supply house (Which is all my fault) when purchasing these instead of doing my own due diligence first. Like they say you can't buy experience but in most cases you can get charged for the lack of it.)
> I'm not sure if I can do the corner ground delta as it becomes a grounded conductor as the compressors are required by the manufacturer to have a fused disconnect with 100 amp JKS fuses in front of them. This seems to be problematic as it appears that the grounded corner conductor can not be fused.
> ...


Use a double pole fused disconnect with an insulated neutral kit. I know for a fact that both Siemens and Square D NEMA 1 fused safety switches are listed for use on corner grounded deltas, and the other manufacturers likely are too. 

Inside of a 3 phase motor controller with fuses, the grounded phase IS allowed to be fused.

You can install a corner grounded circuit for the same price you could a single phase 120/240 volt feeder.... or you can spend more changing the transformers and eating incident costs. I know what I'd do.


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## WEGI (Dec 27, 2015)

Thanks for your response,
Just want to clarify, 
If the existing 3 phase 600 volt fused disconnect is accepted as a motor controller, which I believe it is looking at article 100 definitions,
Can I corner ground the B Phase in the transformer then tape the B phase white and fuse it in the existing disconnect if,
I install the 2 pole disconnect with isolated neutral in front of it per the attached drawing I found on line.
Does the neutral have to be isolated as it looks as if the drawing shows it being grounded in the 2 pole disconnect?
Being that there are 6 transformers of these transformers I am guessing that I have to be very careful that everyone is on the same page it is the B phase that is grounded every time on the secondary and that the primary side are all phased the same in all of the transformers. Which of course they should be anyway.
Sorry for what may sound like stupid questions but I have never come across this before. 

I found this on line, is this what you are thinking.

http://iaeimagazine.org/images/2002_01/02ajohnston_fig3_551727403.jpg

Thanks Paul


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## RePhase277 (Feb 5, 2008)

I believe that pic is actually inaccurate or drawn for an edition of the code that previously allowed the grounded conductor to be grounded twice. You can have your system bonding jumper in either the transformer or the disconnect, but not both. Your grounding electrode conductor needs to connect where ever the bonding jumper is installed.

I personally would hit building steel with a GEC at each transformer, connected directly to the grounded phase lug. Use a 4-port lug on the B phase. Terminate your GEC to one of the ports, your transformer case ground to another, and your white phase conductor and derived secondary EGC to the last two. If there is a disconnect required before the motor controller, use a double pole with an insulated neutral kit and a separate ground lug.

If you have a fused motor controller, use it as you normally would, fuse and all. But the white grounded phase still needs to be white. I have made stickers for the transformer and disconnect identifying it to be a ground B phase system.


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## WEGI (Dec 27, 2015)

Awesome,

Think it finally makes sense to me. Wish I had listened more when I was in class but unless I have a specific application I have a terrible time making sense of these, for me little used installations, first time I have ever needed it in 34 years in the trade. One of the things that keeps me in the trade is that the more I know or think I know the more there is to know.
It would appear that you have saved me a butt load of money and brain damage on replacing these transformers. If I am ever in you neck of the woods I owe you a pint or three.

Thank you sir


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## RePhase277 (Feb 5, 2008)

I see that I missed where you had already taken the GEC to the disconnect, which is OK as well, just don't ground the B phase inside the transformer in that case.

Also, don't connect anything to the X0 terminal on the primary side. Leave it unconnected.


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## WEGI (Dec 27, 2015)

Hey, One more quick question. 
If I take my system bonded jumper from the building steel as you advised earlier to the transformer and tie equipment grounding conductor, case of the transformer and the B phase Grounded conductor together on the 4 pot lug, can I still use my existing 3 pole fused service disconnect and fuse the grounded conductor per NEC 430.36
Thanks again for you time.
Paul


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## RePhase277 (Feb 5, 2008)

Are the fuses the sole overload protection for the motor? Or are there OL heaters in a separate OL relay? If the fuses also serve as OL protection, then you must fuse the grounded phase. But for short circuit and disconnecting only, no fuse in the white conductor.


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## WEGI (Dec 27, 2015)

The manufacturer requires 100amp JKS fuses for overload protection. they won't even do a start up without them.


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## micromind (Aug 11, 2007)

InPhase277 said:


> Also, don't connect anything to the X0 terminal on the primary side. Leave it unconnected.


This is really important. If X0 is connected to anything (even the factory installed bonding jumper) it's a guaranteed burn-up. I don't know why, but I do that it is. Seen it happen more than once.


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## WEGI (Dec 27, 2015)

Thanks, Ill check that XO is totally isolated from everything.


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## inspphild (Dec 31, 2015)

Corner ground Delta, A higher line to ground voltage exists on the other two phase in a neutral - grounded system along with fault switching (opening) is much more severe for cleaning devices and ratings may be greatly reduced, and stabilizing voltages of the ungrounded phases to ground .


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