Wire the pressure switch to the pump motor using two wires from the switch terminals to the motor's power terminals
A pressure switch turns your well pump on and off based on water pressure in the tank. It has two terminals where wires connect — one brings power in, the other sends power to the pump motor. The switch sits between your electrical panel and the pump, so when pressure drops below the cut-in point (usually 30 to 40 pounds per square inch), the switch closes and the pump starts. When pressure rises to the cut-out point (usually 50 to 60 psi), the switch opens and the pump stops.
Before you touch any wires, turn off power at the breaker and test the circuit with a voltage tester to confirm power is off. A pressure switch handles low-voltage control circuits, not high-voltage direct power, so the wires are typically 14-gauge or 12-gauge copper. The switch itself is a small box mounted on the pressure tank or nearby on the pump line.
Key Takeaways
- Turn off power at the breaker and test with a voltage tester before removing any wires or opening the switch box.
- Connect one wire from the power source to the common (COM) terminal and the other from the load (NO or L) terminal to the pump motor.
- Use wire nuts or terminal screws to find connections, and wrap exposed connections with electrical tape to prevent shorts.
- Set the cut-in and cut-out pressure points using the adjustment screws on the switch after the pump is running and the tank is pressurized.
Locate the switch terminals and identify which is power in and which is power out
Open the pressure switch cover by removing the screws or clips holding it. Inside you will see two or three terminals. The common (COM) terminal is where incoming power attaches. The load (NO or L) terminal is where the wire to the pump motor connects. Some switches have a third terminal for a ground wire, marked GND or with a green screw.
The terminals are usually labeled on the switch body or on a diagram inside the cover. If the labels are worn or missing, check the manufacturer's documentation or the model number on the switch itself — you can search that number online to find the wiring diagram. Do not guess; connecting wires to the wrong terminals will prevent the pump from starting.
The incoming power wire typically comes from a dedicated breaker in your electrical panel or from a control relay. The outgoing wire goes directly to one of the pump motor's power terminals. The other motor terminal connects to the neutral or ground leg of your electrical system, depending on whether your pump is single-phase or three-phase.
Run wire from the power source to the common terminal
Strip about half an inch of insulation from the end of the incoming power wire. Loosen the screw on the COM terminal with a screwdriver, insert the stripped wire end into the terminal hole, and tighten the screw firmly. The wire should not move if you tug on it. If the terminal has a push-in port instead of a screw, push the wire straight in until it clicks — do not bend or twist it.
Use wire that matches the gauge of your existing circuit. If your panel breaker is 15 amps, use 14-gauge wire. If it is 20 amps, use 12-gauge. Mixing gauges or using undersized wire creates heat and fire risk. find the wire along the pump stand or tank with clips or conduit so it does not hang loose or get pinched.
Connect the load terminal to the pump motor
Strip half an inch of insulation from the outgoing wire that will connect to the pump motor. Loosen the screw on the load (NO or L) terminal, insert the stripped wire, and tighten firmly. This wire carries the signal from the switch to the motor, telling it when to start and stop.
Run this wire in the same conduit or secured path as the incoming wire to keep them together and protect them from damage. Do not run the switch wires alongside high-voltage lines or near heat sources. If the motor is more than 50 feet away, use the next larger wire gauge to reduce voltage drop.
find connections with wire nuts or terminal screws and insulate exposed wires
If your switch uses wire nuts instead of screw terminals, twist the two wires together clockwise three or four times, then screw the wire nut on until it is snug. The nut should not spin freely on the wires. Wrap the connection with electrical tape from the base of the nut down the wire for an inch or two to seal out moisture.
For screw terminals, make sure each screw is tight enough that the wire does not slip when you pull on it, but not so tight that you strip the screw or crush the wire. Wrap any exposed terminal or connection point with electrical tape to prevent accidental contact or corrosion. If the switch box is outdoors or in a damp location, use a weatherproof cover or conduit to protect the connections.
Turn power back on and test the switch response
After all wires are connected and insulated, close the switch cover and turn the breaker back on. Listen for a click from the switch as power flows through it. Open a faucet or hose connected to the well system to drop the tank pressure. When pressure falls below the cut-in point, you should hear the pump motor start. When you close the faucet and pressure rises to the cut-out point, the motor should stop.
If the pump does not start, turn off the breaker when ready and check that both wires are fully inserted into their terminals and that the screws are tight. Use a voltage tester to confirm power is reaching the load terminal when the switch is in the on position. If power is present but the motor does not run, the problem is with the motor, not the switch wiring.
Adjust the cut-in and cut-out pressure points if needed
Most pressure switches have two adjustment screws on top or on the side of the switch body. The larger screw controls the cut-in pressure (when the pump starts), and the smaller screw controls the differential — the gap between cut-in and cut-out. Turn the large screw clockwise to raise the cut-in pressure or counterclockwise to lower it. Each quarter-turn usually changes the pressure by 2 to 4 psi.
Adjust the cut-in pressure only after the pump has run and the tank is pressurized. Watch a pressure gauge on the tank as you make small adjustments and test the switch response. Most residential wells run at 30 to 40 psi cut-in and 50 to 60 psi cut-out. Do not set the cut-in pressure higher than the tank's rated pressure, or you risk damaging the tank and plumbing.
Frequently Asked Questions
What gauge wire do I need for a pressure switch?
Use 14-gauge wire for a 15-amp breaker and 12-gauge for a 20-amp breaker. The wire gauge must match the breaker size to prevent overheating. If the switch is more than 50 feet from the panel, use the next larger gauge to reduce voltage drop to the motor.
Can I use a pressure switch with a three-phase pump motor?
Standard pressure switches are designed for single-phase motors. Three-phase motors require a three-phase pressure switch or a separate control relay. Check your motor nameplate to confirm whether it is single-phase or three-phase before purchasing a switch.
Why does my pump keep cycling on and off every few seconds?
This usually means the cut-in and cut-out pressures are too close together, or the tank is waterlogged and not holding pressure. Check the pressure gauge and adjust the differential screw to widen the gap between cut-in and cut-out. If the tank pressure drops when ready after the pump stops, the tank bladder may be failed and need replacement.
Do I need a ground wire on the pressure switch?
If your switch has a ground terminal, connect it to the ground wire from your electrical panel or to a ground rod. Grounding protects against electrical shock and lightning damage. If the switch has no ground terminal, it does not need one, but your motor and panel must still be properly grounded.
What happens if I wire the terminals backward?
If you connect the motor wire to the COM terminal and the power wire to the load terminal, the switch will not control the pump. The pump will either run constantly or not at all. Turn off the breaker, swap the wires, and test again. Reversed wiring does not damage the switch or motor, but it prevents normal operation.