480V /240V Single Phase Feeding 3 Phase Panel

[Sean.Day72]

I'm having an issue on a construction project where the contractor purchased a 480/240V single phase transformer to feed a 120/208V, 3 Phase Panel. I'm making the contractor change out transformers, but has anyone seen this in the field before. All the loads are 120V. Basically if the 3 phase panel were to remain just 1 of the 3 phases would be energized, the other 2 would not be used. Is there a code violation with that? besides it just looking silly.

 

[Jraef]

I'm having an issue on a construction project where the contractor purchased a 480/240V single phase transformer to feed a 120/208V, 3 Phase Panel. I'm making the contractor change out transformers, but has anyone seen this in the field before. All the loads are 120V. Basically if the 3 phase panel were to remain just 1 of the 3 phases would be energized, the other 2 would not be used. Is there a code violation with that? besides it just looking silly.

No, TWO of the bus bars would be energized, only one would not (unless they jumped it to one of the others). So long as nobody wants 3 phase power it's functionally OK and quite frankly, done quite a bit on temporary construction site power setups (i.e. "use what you've got handy"). Technically though, it's a violation of the basic "suitable for the intended use" clause of the NEC, but one which, again for temporary site power situations, is often overlooked by inspectors...

 

[Sean.Day72]

You’re right two bus bars would be used with one unenergized. It was an error on the contractors end so he is switching them out . Just wondering if there was a code issue . Also my fault because I didn’t catch it in the submital review . Lesson learned


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[kingpb]

I'm having an issue on a construction project where the contractor purchased a 480/240V single phase transformer to feed a 120/208V, 3 Phase Panel. I'm making the contractor change out transformers, but has anyone seen this in the field before. All the loads are 120V. Basically if the 3 phase panel were to remain just 1 of the 3 phases would be energized, the other 2 would not be used. Is there a code violation with that? besides it just looking silly.

Ironically, when you stated the voltage as 120/208V, you actually stated a single phase service that would be derived from a 3 phase source for use as single phase, 3-wire, open wye application. The proper way to state would be 208Y/120V, however, this is often not the case.

What is on the panel that 3-phase is needed? I can see if the construction power is going to be used later for start-up or testing then you would need it to be 3ph if you have 3ph permanent loads and it was going to be used for this purpose.

 

[kwired]

I'm having an issue on a construction project where the contractor purchased a 480/240V single phase transformer to feed a 120/208V, 3 Phase Panel. I'm making the contractor change out transformers, but has anyone seen this in the field before. All the loads are 120V. Basically if the 3 phase panel were to remain just 1 of the 3 phases would be energized, the other 2 would not be used. Is there a code violation with that? besides it just looking silly.

Some conflicting information in here. 480/240 source but all the load is 120 volts? My guess is source is 480 x 120/240 single phase and you would utilize two of the three buses if using the three phase panel.

If you configured the transformer secondary for 120 only, because you are not supplying anything but 120 volt loads you could tie all three bus panels together and then all spaces would be available to use, you would likely do same thing with two bus single phase panel if only supplying with 120 volts.