I would think that the obvious reason the breaker is tripping is that the motor
is drawing more than 40 amps. In the absence of any contrary indicator, I don't
see that anything is necessarily wrong. Ugley's says, in its table headed
"FULL-LOAD CURRENT AND OTHER DATA : THREE PHASE A.C. MOTORS":

10hp 230V 28amps 60A breaker #2 starter 32.2A heaters #10 wire 3/4 EMT

So from that I would conclude that even though the full load amp rating is only
28 amps it can draw a bit more so if I were you, everything else being met, I
would simply replace the 40A breaker with a 60A breaker.

Grant Erwin
Kirkland, Washington

"gtslabs" wrote in message
ups.com...

I picked up a 10 hp compressor, dual heads, 2 stage, 120 gallon tank.
The Pump has a centrifical unloader. The Motor is 3 phase 240 of which
I run on my 10hp rotary phase converter wired with 8-3 With Ground and
a 40 amp breaker.
The compressor starts fine but the breaker trips when the compressor is
near its top end around 160 psi. What are some causes for the breaker
to trip?