im trying to get two compressors to work of a single pressure switch?thanks a lot!
AC motors normally have a starting current of 5 to 7 times the normal running current. Hence for longer contact life, you should have at least 63 Amps rated switch. Also, it is not advisable to operate the motors directly from the pressure switch. Use a contactor rated 63Amps (or higher) and wire the pressure switch in series with the coil of the contactor. Connect both the AC motors via the contactor. This way both the motors wil work on a single pressure switch and the pressure switch will have a long life.
Assuming both these compressors are supplying the same reservoir, you can use a common pressure switch. But starting current will be well in excess of your 30A. contacts. A better way would be to have the pressure switch supply a heavier current rated contactor, and use the contactor to switch the motors.
At a time one in service it can be ok, other should be off .Keep Individual 30 Amps p switch for each compressor .If it is 1 30A switch If accidentally started both compressor it will weld the 30Amps p switch. Unless you should make Interlock using with Individual Power contactor.If you need both in service you have to modify the circuit with (programmable) timer circuit.
The starting current for the two motors would be near 100 amps surge. The motors would need to be on their own circuit breaker. As for the pressure switch controlling both motors, pressure switches are usually designed to operate a single motor. Going through a contactor would be your best solution with the pressure switch controlling the contactor coil.
