Can a transformer just feed receptacles?

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Bosco

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I have a plant I'm working in has a 3 phase 480 volt panel. The electricain wants me to install a transformer and a 2 pole disconnect to feed receptacles one phase to each receptacles. I looked in 450 and didn't see anything that wouldn't let me have the receptacles as the load (unless I missed it). If it is possible here are some questions......

1-would I just calculate each receptacle at 180 VA? What would be the formula for sizing this situation? OC protection?.

2-Can I use a 3 phase transformer and just use 2 legs with a 2 pole disconnect? Can you buy a single phase 480-208 volt single phase transformer?

Thanks for any input in advance.
 
Bosco said:
I have a plant I'm working in has a 3 phase 480 volt panel. The electricain wants me to install a transformer and a 2 pole disconnect to feed receptacles one phase to each receptacles. I looked in 450 and didn't see anything that wouldn't let me have the receptacles as the load (unless I missed it). If it is possible here are some questions.......
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Art 450 doesn't really address the load. It simply gives you the specifics of how the transformer must be protected after you determine the load
Bosco said:
1-would I just calculate each receptacle at 180 VA? What would be the formula for sizing this situation? OC protection?..
Click to expand...
I would think in this case you best get a pretty good detail of the actual planned load. The actual load and the diversity (how much of the load will operate simultaneously)
Bosco said:
2-Can I use a 3 phase transformer and just use 2 legs with a 2 pole disconnect? Can you buy a single phase 480-208 volt single phase transformer?

Thanks for any input in advance.
Click to expand...
You can connect a single phase transformer to a 3 phase supply by simply using any two phases. Single phase transformers are more common as 480 to 240 or 480 to 240/120. If you actually need 208 you may find it more practical to stay with a 480/208Y120 3 phase transformer.
Your game plan should be (a) determine the exact load (KW), (b) select the transformer, (c) protect it per Art 450, and (d) protect the loads per the appropriate article (210, 430, etc) and, (e) protect the conductors per Art 240./
 
I think Gus pretty well covered it. If you need 208 single ok, but not as common a need as 240 to feed say a 220 or 230 volt load.

If you can't get good info for the loads best to plan for 100% of the device rating(s). Don't forget the grounding requirements of the separately derived system.
 
Charlie, I asked after looking at his profile "contractor" I believe and his past questions. No ill will just trying to gauge who,what w,w,w.
 
Thanks for the help. I couldn't actually find anything in the code that preventing me from doing this. I can get away with 240. They actuall just want two 120 volt outlets for an energy management system so the load will be very little. So I guess I would figure 180 VA per outlet and size the transformer accordingly.

Thanks again
 
As noted in 240.21(C)(1), if the primary is protected per 450.3 and that OCP, when multiplied by the secondary/primary ratio does not exceed the secondary conductor ampacity,
In the OP's situation 480/120 or 4 to 1. So 20 amps secondary conductors, 5 amp primary fuse.
 
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