Wire size for 208V Primary to 480v sec y transformer 112.5kva

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petroc

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Location
New Jersey
Occupation
electrician
Was looking for a little help on wire size and primary breaker size for 112.5KVA transformer 208v primary 480V Y sec also grounding size
 
The conductor size is dependent on the over current device protecting it.
Look at you transformer currents and protect the transformer per 450.3
If you elect to go the 125% primary current rule then your 112.5 kva transformer would require a 400 amp breaker and you would size the conductor accordingly.
With properly sized secondary protection you could use a larger primary breaker and if you choose that route you would still size the conductor based on the over-current device.
 
In addition to the conductor size question, just so we are clear, is this a step up application with a 208 volt delta primary and a 480Y secondary?
 
In addition to the conductor size question, just so we are clear, is this a step up application with a 208 volt delta primary and a 480Y secondary?
Yes the main panel has 400A and need to hook this up for Granite saw application.about a 20ft run to shop.
Transformer provided to my customer from the saw manufacturer is a 112.5 KVA 208V PRIMARY 480V y/277 secondary
 
If the panel already has a 400 amp I would check the lugs to see if they accept two conductors and if so I would likely run parallel 3/0s, if not, a 500 kcmil.
Don't forget with a 480/277 secondary you will need to establish a grounding electrode system.
 
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