Single phase 240V loads on 240V 3 phase transformer.

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Raventai

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Alachua Florida
I maintain a mid sized factory here in Florida, we have two mail electric suplies from the electric utility, 3 phase 480/277 and the other 3 phase 208/120, we have no native 240V supply.

this has been a bit of a problem with contractors equipment, especially now as we are doing a renovation, some 240v tools will run on the 208, some contractors not comfortable hooking their equipment to it. and I don't not have 208 handy in many places, it is generally distributed as 120v oultets. for instance today I have floor grinders here polishing the floor, the closest 208 pannel is 200' from where they are working,

What do I have throughout the facility is 60 amp 3 phase 480 volt outlets for our welders.

I also have a 75 KVA 3 phase transformer, 3p 480v to 3p 240, Square D style 3439-28212-016

what I would like to do is bolt this transformer to a pallet with a cord and the same 480v plug as our welders and feed the 240v output to a breaker box also mounted on the pallet with 240v outlets, what i envision is being able to fork this thing to where contractors are working and provide 240v outlets they can plug into, the 60 amp of our welder outlets is a bit small to fully power the transformer (90 amp input for 180 amps output) but I should still be able to get 100-120 amps out with 60 in. my plan is to set this up and then have our electrical contractor look it over before use,

problem is I am not sure how well this transformer will like the unbalanced load of picking off one phase, if i have 3 identical tools running I may get some balance, but that would be rare, would that be a problem? what else should I look out for?
 
The transformer will not mind an imbalance as long as the load on each winding is always less than the rated maximum.
For example if the transformer can power a three phase load with line current on each line being 20A, then it could power a single phase line-to-line load of 20A with no problem.
It could also handle an unbalanced single phase load of somewhat more than 20A, but you do not need to go there!
 
What are you going to do about the required grounding electrode for the secondary side? Are you going to operate it as a corner grounded system? If not, then you need a ground detector on the secondary side.
 
Gold digger, thank you for the info about unbalanced load.

Don, I am not that familiar with corner grounding, the three phase we use here is 4 wire, 3 phases and a ground, sometimes a neutral,

I was planning on just passing on the ground from the 480 plug to the 240 side, bonding the case of the transformer, and the 240 panel, emt outlets, etc

would that not be correct? Do I need corner grounding?
 
Yes, the secondary windings will need a ground reference. If there is no center tapped winding (to provide 120 services) then corner grounded is all you can do. An odd concept the first time you see it, but you are required to ground the secondary for safety. Unless you are on an old Navy vessel...
 
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