480 240/120 transformer

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220wire

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I have a single phase 480v primary 240/120 secondary. If I do not install a grounded conductor with the primary, would I bond the transformer case to the center tap (sized to the secondary conductors)?
 
this still doesnt make sense. I have two #4's for the primary with a #6 egc. If the transformer case is bonded to the center tap of the transformer than the way I am looking at it is the #6 is carrying the unbalance and possibly the fault current. Am I way overthinking this?
 
When all is done , the center tap , the #6 egc, the transformer case, and the egc's of your primary will all be bonded at the same place electrically. There will be no unbalanced current in your primary. The egcs in the primary do not carry unbalanced current. They are for fault current. The grounded conductor in the secondary carries unbalanced current. Bonding all this stuff together is only for safety.
 
The primary and secondary windings are isolated from each other. Your EGC with your primary is bonded to the case for a ground path should the primary fault to the case.
The secondary XO bond is there to protect in case of a fault on the secondary to case.
Each serves it's own purpose and there should be no current flow under normal conditions.
 
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