Corner Grounding?

[jimdavis]

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?

 

[ActionDave]

Yes, you would need a corner ground or ground detector. Buying a tanning bed that runs on 208V is a much better solution, or get a transformer with a center tap on the delta side.

 

[texie]

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]

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]

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]

But, if you do, be sure to leave the now-primary neutral terminal floating, as if it was a delta.

 

[jimdavis]

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.