Xfrmr Size

mstrlucky74

Senior Member
Location
NJ
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.
 
Last edited:

tw1156

Senior Member
Location
Texas
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
Location
Michigan
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.
 
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
Location
Michigan
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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