What Would Be The Right Size Transformer.

Power Coming In Would Be Single Phase 480

Output Is 120v , About 4.2a

I Figure About 1kva Would Be Plenty

Since VA (AC Power) is volts times amps:
120 VAC X 4.2 Amps= 504 VA
So the 1.0 KVA xfer is almost double what is needed, offering plenty to spare, if the load is resistive. If the load is inductive, such as a motor, it is just about the correct size.

Quote:

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Originally Posted by MRCHAD

What Would Be The Right Size Transformer.

Power Coming In Would Be Single Phase 480

Output Is 120v , About 4.2a

I Figure About 1kva Would Be Plenty

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I think you'll probably be OK. I think you just need to multiply your 120*4.2 and w/ a 1 KVA rated supply you would have a safety factor of 2.