Is there any other way to operate a 3 phase air compressor pressure switch other than using a starter? Am looking for an inexpensive way to wire the unit by just using a 3 pole fused disconnect. Can't think of any way to have the motor drop out when the switch reaches the desired pressure other than de energizing a coil on a starter. Thanks
Sure just use a shunt trip breaker so that the pressure switch trips out the breaker everytime is reaches the set pressure, but I don't think thats what you want, and I agree with Cow without overloads this motor would not last long as the first time it dead heads into a full pressurized cylinder someone will be replacing the motor.
You could get a two pole pressure switch (depending upon the HP rating) but I would still at least use a manual motor starter ahead of it to protect the motor.
Keep in mind that not any pressure switch will work, as one for an air compressor will have a head bleed off line to remove the head pressure so the motor does not dead head in to a locked load.
The best setup I like is the motor starter that has the bleed off valve built into the contactor, the reason is, I have had many who like to turn off their compressor at night and then try to turn it back on in the morning, if the system is tight and holds pressure then since it was turned off before the bleed off valve was activated it will trip on over loads or breaker when they try to turn it back on, with bleed off done with the contactor then it will bleed off when they kill the power.