Well Pump Pressure Switch Wiring Guide

Pressure Switch Safety Warning

What Is a Pressure Switch?

The pressure switch is the gray box mounted near your pressure tank that controls when the pump turns on and off. It contains a pressure-sensing diaphragm connected to electrical contacts. When pressure drops to the cut-in setting, the contacts close and start the pump. When pressure reaches cut-off, the contacts open and stop the pump.

Identifying the Terminals

Open the pressure switch cover. You will see a set of terminals inside:

• LINE terminals — incoming power from the breaker panel (2 wires)
• LOAD terminals — outgoing power to the pump (2 wires)
• Ground terminal — green screw, connects to ground wire

LINE and LOAD terminals are usually labeled on the switch body. If not, the LINE wires typically enter from the bottom conduit and the LOAD wires exit toward the pump.

Step-by-Step Wiring

1. Turn off breaker. Verify with voltage tester.
2. Photograph all existing wiring before disconnecting.
3. Loosen terminal screws and remove wires from old switch.
4. Mount new switch on the pipe fitting.
5. Connect LINE wires to LINE terminals — tighten firmly.
6. Connect LOAD wires to LOAD terminals — tighten firmly.
7. Connect ground wire to ground screw.
8. Replace cover, restore power, test.

Setting the Pressure

Most residential pressure switches come pre-set for 30/50 PSI. To change to 40/60: remove the cover and turn the large adjustment nut clockwise (increases both cut-in and cut-off together). Make small quarter-turn adjustments and test with the pump running. After changing the switch setting, always adjust the tank pre-charge to 2 PSI below the new cut-in pressure.

When to Replace vs Adjust

Replace the pressure switch when: contacts are burnt or blackened, the switch fails to shut the pump off at cut-out pressure, the switch fails to start the pump at cut-in pressure, or the switch is physically damaged. A new pressure switch costs $15-35 at most hardware stores.