480V-240V transformer with #10AWG on 480V side....

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Benton

Senior Member
Location
Louisiana
Hey I am planning to install two compressors that are 208V single phase. They each pull 21A. I have access to 480V 3phase circuit that is being fed by #10 wire. I was wondering if a place a 10-15KVA step down tranformer in between that 480 circuit, being that it is consider a separately dirived system (or is it in this case), do I need to worry about the wire size on the 480 side?
 

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
First of all, you can?t supply a machine with 240 volts, if it is rated for 208 volts. If the manufacturer has rated it to handle both voltage levels, then you can use the transformer that you named.

Secondly, regardless of whether a transformer is configured in such a way as to establish a separately derived system, you always have to worry about the sizes of the wires on both sides of the transformer.


Third, I don?t understand what you mean by saying the transformer will go ?in between that 480 volt circuit.? Do you mean that there is an existing circuit that has its own breaker (likely a 30 amp), a #10 wire, and some downstream load, and you intend to connect the primary side of your step-down transformer to that #10 wire, at some point ?in between? the existing breaker and the existing load? If that is what you mean, then yes you can do that, but only if (1) the wire you use as the primary to your transformer is no smaller than #10, and (2) the total load on the combined circuit (i.e., the new transformer and compressors combined with the circuit?s original load) does not exceed a total of 30 amps.

 

Benton

Senior Member
Location
Louisiana
First of all, you can?t supply a machine with 240 volts, if it is rated for 208 volts. If the manufacturer has rated it to handle both voltage levels, then you can use the transformer that you named.

Secondly, regardless of whether a transformer is configured in such a way as to establish a separately derived system, you always have to worry about the sizes of the wires on both sides of the transformer.


Third, I don?t understand what you mean by saying the transformer will go ?in between that 480 volt circuit.? Do you mean that there is an existing circuit that has its own breaker (likely a 30 amp), a #10 wire, and some downstream load, and you intend to connect the primary side of your step-down transformer to that #10 wire, at some point ?in between? the existing breaker and the existing load? If that is what you mean, then yes you can do that, but only if (1) the wire you use as the primary to your transformer is no smaller than #10, and (2) the total load on the combined circuit (i.e., the new transformer and compressors combined with the circuit?s original load) does not exceed a total of 30 amps.



Thanks, this is exactly what I was asking about. and sorry the repeat thread.
 
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