Optional* The Checkpoint power supply is not needed if you have your own power source. The Power Supplies for the Checkpoint System power up using a 110vac that converts to 24vdc. The 24vdc is used to operate the checkpoint and the coils on the relays that are being switched. The wire colors on the power supply match up color for color to the Checkpoint units, making the hook-up easy and fast. There are either 1, 2, 3, or 4 relays on the power supply depending on the Checkpoint Model you are choosing. The relays are set up with 110vac running through the contacts using the same 110vac circuit which powers the power supply. These 110 switched circuits are intended to drive 110 coil(s) on a contactor that's large enough to operate the pump being used. They are also rated to drive solenoid or motorized valves directly. The Relay contacts are rated 30amps @ 240vac. The relays are a Form C, SPDT relay with both a N.O. and a N.C. set of contacts that are intended to break only the hot leg.