3 phase to single phase

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aftershock

aftershock

Senior Member
Location
Memphis, TN
120/208 3 phase from the city transformer to a 3 phase meter base then to a 100 amp 3 phase disconnect and then just 2 hots off the load side of the disconnect a neutral and ground to a 100 amp single phase panel.

Anyone see a problem with this?
 
Other than possibly creating an unbalanced load for the transformer, you should be fine, I would use the lightest loaded two of the three phases and watch what gets put on this panel.
 
hillbilly1 said:
Other than possibly creating an unbalanced load for the transformer, you should be fine, I would use the lightest loaded two of the three phases and watch what gets put on this panel.
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There isn't a code violation with this setup?
The reason I asked is I have never had to do anything like this before, but my boss says we will do it this way and we will be fine with the inspection.

I doubt the load would reach even 40 amps across both phases. 5 - 110 circuits if I remember correctly.
 
Why the extra step then? I don't understand the reasoning for two panels. You can just as easily take the 5 circuits out of the 3-phase panel.
 
Not any violation that I know of, many computer rooms use single phase UPS units to power a single phase panel from a three phase service. It's just like adding a large single phase load, such as single phase motor or oven or the like. You just have to keep the load relatively balanced on all three phases to avoid other power problems.
 
Not a problem. The only thing would be if you were feeding three phase equipment and then feed the single phase panel as stated you would need to watch the phase balance.
 
480sparky said:
Why the extra step then? I don't understand the reasoning for two panels. You can just as easily take the 5 circuits out of the 3-phase panel.
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It's a drive up ATM. Building is prefab and prewired, panel included. It sits in the middle of a parking lot. Those "above me" have done all the paperwork and had us come from a current transformer somewhere near this install.
Once the building arrived and was errected, I opened the access door and noticed the 14 1/2" high by 12 1/2" wide single phase panel. Keep in mind, this after everything else was done,, the boring, the piping, even the 4' deep concrete.
I called the POCO to see if I could get just single phase from the transformer. No I cant,, Im getting 3 phase. OK, I asked the boss to find me a 3 phase panel to replace the one in the structure. Cant find one that small and we have to have this thing up and running by friday.
So,, this is how I was told I am going to do this.
 
Don't know why the POCO couldn't run single phase from the three phase transformer, unless their single phase meters will not work with it, somebody on here probably works for a POCO and could answer that question. I know they do it in South Carolina, because they screwed me on a pylon sign, they tapped off of a 120/208 three phase pad mount to a single phase meter, well I needed 277 for sign the anchor store for the shopping center put up. Used a 3KVA transformer 240 volt to 277, Had to change the taps to 120 to 277 because the 208 left me a little shy on voltage. Doubled the size of the primary wire and breaker.
 
The only additional problem I can see will not likely apply to your installation. The problem would come into play if the customer needed 220 to 240 volts for a single phase load. You could only supply 208, and that is not likely to be adequate. But it sounds like all your loads will be 120 volts.
 
charlie b said:
The only additional problem I can see will not likely apply to your installation. The problem would come into play if the customer needed 220 to 240 volts for a single phase load. You could only supply 208, and that is not likely to be adequate. But it sounds like all your loads will be 120 volts.
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I do hope I get no more suprises. I got the service equipment mounted and all the wire pulled today. I hope to get my service release insp tomorrow so the POCO will hook it up at the transformer and issue the meter. I got 2 22' high pole lights to install next to this thing. These are the only 2 things that could be 208v. I was told the heater/ac unit is 110v but that access door is blocked by one of the ballords <sp>. This thing is suppose to be all prewired, all I have to do is get a circuit to the atm and wire the pole lights.
 
Sound fine to me, I wouldn't worry to much about the POCO transformer balancing as this is not the only load off there transformer, the balance will come in from other users on the same Xfmr.
 
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