Are the motors truly in parallel? As in; all three legs of one motor
connected to all three legs of the other motor? If so, you should see some
3rd leg current between the motors. Is there a separate switch on the 1/2
HP motor? If they are in parallel you should be able to switch on and start
the 1/2 HP motor *after* the 1.5 HP motor is up to speed. The larger motor
will be generating some unbalanced 3-phase power by transformer action. It
is acting like an idler motor in a rotary phase converter configuration.

Bob Swinney
"Charles A. Sherwood" wrote in message
...
With a static phase converter, zero current in the third leg is normal
(after the brief starting interval) when you are running a 3 phase
machine
on single phase current. The third leg is only intergized for starting.

But in this case I have two motors in parallel. The big 1.5HP grinder
motor and the little 1/2 HP blower. The big grinder motor is pretty
much unloaded and the the blower motor which is always loaded because
it is moving lots of air. I expected to see some current in the third
leg but I don't see any.

chuck