Transformer feed ( One size smaller )

Davebones

Senior Member
Is there a issue if one conductor feeding a 3 phase transformer ( 480 - 120 208v ) is one size smaller than the other two phases as long as it's rated for the primary fuse size ? Is there a code prohibiting this ?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
As long as the condcutors are protected at or below their ampacity there is no issue. Any particular reason why you would do this?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Is there a issue if one conductor feeding a 3 phase transformer ( 480 - 120 208v ) is one size smaller than the other two phases as long as it's rated for the primary fuse size ? Is there a code prohibiting this ?
I don't recall anything in the code would prohibit this, as long as the conductor is properly protected.

A little unusual though.

I suppose it could get small enough that it would not meet the minimum size for the calculated load. That would be a code problem.
 

topgone

Senior Member
Is there a issue if one conductor feeding a 3 phase transformer ( 480 - 120 208v ) is one size smaller than the other two phases as long as it's rated for the primary fuse size ? Is there a code prohibiting this ?
What what are your transformer loads? If you have motor loads, you have to be aware that there are limitations as to the voltage imbalance to prevent excessive motor heating. The motor temperature will increase to twice the square of the voltage percent imbalance (2 degrees C for 1% imbalance; 8 degrees C for 2%, etc).
 
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