480V primary to 208V secondary

[nchrist2]

I have a project where we are pulling power from a 480V 3 phase panel and feeding it through a transformer to make it 208V 3 phase. However, the breaker that is before the transformer is a 50A breaker. After the transformer we feed into a panel with a 100A breaker on the secondary side. I was told that because the primary side is 480V that it should be able to handle the 100A secondary side without tripping. Is this true?

 

[Buck Parrish]

False................

 

[charlie b]

I would say "true." If the secondary current is 100 amps, then the primary current will be 100 times 208 divided by 480, or 43 amps. That would not trip a 50 amp primary breaker.

 

[jrannis]

Sounds right. What size is the transformer?