Xfrmr Size

mstrlucky74

Senior Member
Approx what size xfrmr for 125a 480v panel on primary side and 120/208 60A panel on secondary side? Thanks.

Sorry 50A 3P breaker feeding the transformer. I get 45kva.
 
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tw1156

Senior Member
30kVA, and in reality you could make that a 100A panel on a 30kVA on the secondary side, but 60A CB is not a problem.
 

S'mise

Senior Member
If you need 60 amps at 208 3phase to feed your load. 208 x 1.733 x 60= about 22kva or more.

Using panel size or breaker sizes is not the best way to size it.
 

WA_Sparky

Member
Approx what size xfrmr for 125a 480v panel on primary side and 120/208 60A panel on secondary side? Thanks.

Sorry 50A 3P breaker feeding the transformer. I get 45kva.
If you're only trying to provide power to a 60A panel on secondary side
30KVA transformer
Primary side = rated max = 36A 480 3Ø, 50A/3p breaker for protection,
Secondary side = rated max 83.3A available at 208 3Ø, 100A/3p protection

You could always drop your secondary OCP to 60A/3p and call it a day.
 

S'mise

Senior Member
If you need 60 amps at 208 3phase to feed your load. 208 x 1.733 x 60= about 22kva or more,Using panel size or breaker sizes is not the best way to size it.
I misunderstood that you were trying to figure out the size of an existing x former by looking at the 50a breaker feeding it.

30kva would use a standard 40a breaker. You have a 50a.
45kva would draw more than 50a breaker protecting it.

Base on 480, 3 phase using a 50a breaker feeding the primary, it could be anywhere from 38 to 41kva.
Although oversized for a 60a loaded secondary.
 
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