Primary input

[nizak]

I have a grinding machine that requires 480V 50A 3phase input. I am deriving this from a 240V 3phase system supplying a step up transformer. With the existing load center that I have I am limited to a 3 pole plug in QO breaker rated at 100A. The distance to the disconnect supplying the transformer is approx. 50 feet, does this input sound realistic for what is trying to be accomplished. Thanks.

 

[bkludecke]

Yeah, sounds right to me. As long as the wire is sized right. There will be a bit of loss through the xfrmr but most machines don't operate at FLA anyway and overloads are generally sized @ 125%. Yeah I'd go for it. I assume that there is adequate capacity in the 240 volt panel board to add the load, right?

 

[coulter]

I have a grinding machine that requires 480V 50A 3phase input. ...

If the 50A is nameplate FLA and the load is mostly the one drive motor - 100A on the 240V feeding the xfm sounds way too small. Try this:
What 480V CB would you normally use to feed the grinder? Take into account all the 430 stuff.

Multiply that times two and that would be a good starting place for the 240 CB.

carl