Maintenance area with several 240V/1ph and 240V/3ph loads. Should we add a 240V delta transformer? Where or how do we establish ground?

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jcarter0524

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We're designing a new maintenance building where they are moving over existing machinery. Most of the machinery is listed at 120/240V 1ph, 240V 1ph, or 240V 3ph. We already designed for a 120/208V 3ph system. We thought it prudent to add an "Equipment Panel" at 240V/3ph delta, but can't agree on how to ground it. Corner ground? Add "ground fault detectors" in the main circuit breaker? If we design a 240V/3ph panel, establish an earth ground for the ground bus, then there is no ground reference in the 3 hot conductors, right? The equipment ground conductor grounding the metal casing of the equipment does nothing to protect the person leaning on it, right?

Another option is to provide a 120/240V 3ph hi-leg delta panel without a neutral bus. Less expensive transformer. And you'll have 120V to ground on 2 of the 3 phases. I believe 3rd phase will be 208V to ground, but still better than corner ground with 240V to ground.

Any input would be most appreciated.
 
Forgot a point - Any machinery calling for 120/240V 1ph we assume can run on 120/208V 1ph. So do not plan on having 120V available in the delta panel.
 
jcarter0524 said:
... We already designed for a 120/208V 3ph system. We thought it prudent to add an "Equipment Panel" at 240V/3ph delta, but can't agree on how to ground it.

Another option is to provide a 120/240V 3ph hi-leg delta panel without a neutral bus. Less expensive transformer. And you'll have 120V to ground on 2 of the 3 phases. I believe 3rd phase will be 208V to ground, but still better than corner ground with 240V to ground.
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jcarter0524 said:
Forgot a point - Any machinery calling for 120/240V 1ph we assume can run on 120/208V 1ph. So do not plan on having 120V available in the delta panel.
Click to expand...
Here's my take:
You have 120V, 1ph, and 208V, 1 phase covered. The 240V, 3phase panels is only for three phase loads - no 120V loads. The question: How to ground the 240V, 3ph panel?

Consider a 240V/139V, 3phase, 4wire, grounded Wye. A standard 3ph, 240V panel will work fine. Transformers are normal, maybe not off the shelf, but readily available. Ground detectors not required. If there is a concern that someone, sometime will try to use a 1pole line to neutral circuit (JP Stapp, Edward Murphy), put a nice big red placard:
Do not use 1 pole circuits in this panel
It will fry your toenails
And that always smells bad

I don't particularly like corner grounded delta, high leg delta, or ungrounded delta either.
 
I agree with LarryFine, a 4 wire 'high leg' delta.

However since you are already planning on 2 panels, segregate things so that you have a '120/240' panel with the neutral bus, and a 240V panel without the neutral bus. This way you don't have the 'wild leg' and the neutral bus in the same panel.

-Jon
 
---> Grounded 4 wire delta. <---
That is the best choice.
however why have the 208Y120 at all?

@iceworm is on the right track however if you just take the tap changer up all the way on the pad-mount 208V transformer (you presumably alredy have) you get a Brazilian 220Y127.
All your 240V equipment will run great on that and so will the 208.
220Y127 is not out of spec ( ANSI C84.1 whatever it is) its just not caught on here yet.

If you want to skip the 120V altogether and have 100kVA or more in load get a huge savings and consider a 415Y240 also especially if your already using a bolt to buss panel-boards. This is becoming a very common system.
 
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