I would temporarily hook up the compressor to see how the exposed fans move air. Which direction is it pushing out of, or if the fans are opposed pushing air thru the motor, or drawing it out.
Is there a threaded boss on the compressor, or some place you can hook the ground wire to?
I can find a way to ground it I am sure. As far as the original issue with the correct breaker based on the motor plate, what would you recommend?
Dave
With a PSC motor, I would not go heavy on the trip curve as inrush current is rather low. UL-489 rated 6 amp with a "C" trip curve should work well.
6A CB Would be nice to get a 5.5A, but they don't make them. This will instantly trip if it sees 30 amps, then in less than one second the curve kicks in, which is time-temp dependent.
Circuit/device protection is fairly complicated to explain due to the myriad of devices and laws in place and available.
A customer had a brand new 1/4hp 115V single phase motor on a rig. They tried to start it and smoke was coming out, so they shut it off quick. It had built in thermal protection, which by design should have tripped within 10 seconds, as with all thermal protection by law. Went there and hooked up meters. Kicked it on for a couple seconds, saw smoke, meter said it was eating 32 amps. If we waited for the thermal protection to wake up and kick in, motor would have been melted. Motor was way too small for what they wanted it to do. Temporarily hooked up the correct CB to it to show them, and every time they tried to start it under the overload conditions it instantly tripped. Pulled the motor off the load and all was cool. I can stop/stall a 1/4 hp motor with my hand like I'm sure most can, but wear leather gloves. Put the squeeze on it and had them watch the meter on how the amps climb way over SF (Service Factor), but the thermal overloads were still sleeping. Should have tripped, but they didn't. CB caught it way before damaging overload and tripped.
Carry On...
