Corner Grounding?

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jimdavis

Senior Member
A colleague of mine is overseeing a new construction tanning salon. The service to the salon will be 208Y/120V. The tanning beds are rated 240V 3 phase. His drawings call out a reverse-fed 240V delta- 208Y/120V transformer feeding a sub-panel to power the beds. I told him he may need to corner-ground the 240V side of the transformer. Looking at 250.20(B)(1) I'm not sure this applies. Any thoughts?
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I agree, Dave. I would go a step further and use a 208 delta primary X 240 delta with center tap (for grounding purposes) secondary. But before I did that I would want to know for sure that these are straight 240 volt and not 120/240 as that would change things.
 

jimdavis

Senior Member
Thanks guys. At this point I'm advising my colleague based on what he has described to me. I believe the transformer has been purchased already. I told him to send me a picture of the nameplate when it arrives so I can be certain of what he is dealing with.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Thanks guys. At this point I'm advising my colleague based on what he has described to me. I believe the transformer has been purchased already. I told him to send me a picture of the nameplate when it arrives so I can be certain of what he is dealing with.

I would not even consider using a
reverse-fed 240V delta- 208Y/120V transformer as proposed for a number of reasons.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
But, if you do, be sure to leave the now-primary neutral terminal floating, as if it was a delta.
 

jimdavis

Senior Member
I would not even consider using a
reverse-fed 240V delta- 208Y/120V transformer as proposed for a number of reasons.

Nor would I. Although we are a design-build EC we didn't do the engineering on this project. As foremen in the field sometimes we are left trying to make code-compliant installs of someone else's poor decisions. Hopefully this guy's transformer turns out to be a 3-phase 4-wire rather than what he's telling me.
 
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