I have an aerator pump in my septic tank that runs continuously. I want to wire a timed septic pump to the same circuit so that the aerator turns off when the septic pump turns on.
1 Answer
You need a double-throw relay. Either a single pole, double throw, or double pole, double throw, relay depending on the voltage of the devices. Well, I guess some folks do switch only one side of a 240V motor, on the USA/Canada system, but I don't. In a 220-250V line to neutral country that makes sense. with 120V line to neutral it's better (IME) to switch off both lines to a 240 motor.
Contacts of the relay will need to be rated for (preferably conservatively far above) the motor load of each motor or you'll end up with them welded one way of the other in short order.
Power from the breaker goes to the common terminal of the relay. Aerator presumably would go to the normally closed contact, pump to the normally open contact, and pump control to the relay coil. In fiddly relay esoterica, the contacts should be "break before make" so the aerator is fully disconnected before the pump is connected.
