# Transformer conductor sizing calculations



## SteveBayshore (Apr 7, 2013)

Am I missing something?
Why are you using a 45kVA transformer for a machine that draws 12 kW, or am I missunderstanding you? Secondary side of 45kVA transformer is rated at 125 amps at 208 volts. 45,000/(208x1.73)=125 amps Can you get a transformer that has the secondary voltage rated for 220 volts, to match the machine? A transformer with a 230 volt secondary will output a closer secondary voltage to match the machine. If the transformer has taps, you should be able to get pretty close to 220 volts. Don't forget to change your calculations if you change voltages.


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## Pacific81 (Feb 19, 2010)

It is the transformer my manager got for the machine, the machine has been moved so the original scope has changed he had got a 200A disconnect 2/0 cable for the secondary side, I didn't know weather to calculate the power of the machine or the kva of the transformer. I am just trying to understand how to perform the calculations correctly. I've got my code book out and Mike Holt book.... time for some studying I think


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## wildleg (Apr 12, 2009)

most of what you need to know is in table 450.3 B


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## BBQ (Nov 16, 2010)

wildleg said:


> most of what you need to know is in table 450.3 B


Does that apply in Manchester England?


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## wildleg (Apr 12, 2009)

BBQ said:


> Does that apply in Manchester England?


heck if I know. hehehe

does Mike Holt write for the code books in England ?



Pacific81 said:


> It is the transformer my manager got for the machine, the machine has been moved so the original scope has changed he had got a 200A disconnect 2/0 cable for the secondary side, I didn't know weather to calculate the power of the machine or the kva of the transformer. I am just trying to understand how to perform the calculations correctly. I've got my code book out and* Mike Holt book*.... time for some studying I think


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## BBQ (Nov 16, 2010)

wildleg said:


> heck if I know. hehehe
> 
> does Mike Holt write for the code books in England ?


:laughing: I did not see that.


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## Pacific81 (Feb 19, 2010)

This has cleared things up a bit! http://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/TransformerInstallation~20020516.htm 

I live in San Diego now.... need to change my details.


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