DIY Wiring for a Square D Pressure Switch

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If you're trying to control pressure in an air compressor or a water pump, using a Square D pressure switch will do the trick. A water pump pressure switch tends to operate at a lower pressure, while an air compressor operates at a higher pressure. That being said, the wiring of any Square D pressure is basically the same.


How to Test a Square D Pressure Switch

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A Square D pressure switch, which is what controls the pump, will likely be mounted on the outside of your pressure tank. Over time, a Square D pressure switch can become worn out. An older pressure switch can lead to issues with your pump. If your pump isn't switching on or off properly, it may well be to do with your Square D pressure switch.


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To test your switch:

  1. Gently tap it with the power on and listen for a click. If that happens, the switch may have been stuck and may work now.
  2. If the same problem recurs, it's time to replace the switch.

How to Choose the Right Pressure Switch Replacement

If you decide to remove and replace your Square D pressure switch, check the pressure range of your old switch — it will be either 20-40, 30-50 or 40-60 PSI. You can find this information under the cover, which can be pulled off. Always replace your pressure switch with one of the same pressure.

There may also be information on the amperage rating and information on whether the switch can be used for water systems or air compressors. The value of your motors amperage capacity should be lower than the amperage rating of your new pressure switch.

How to Install a Square D Pressure Switch

  1. Make sure your pump is switched off. Before starting your Square D pressure switch installation, double check for safety.
  2. Begin to disconnect the old wiring.
  3. Close the pressure tank's valve, then safely drain the pressure tank.
  4. Remove the old pressure switch.
  5. There will be two sets of wires, one set from the power source and one set from the pump motor. Make a note of how these connected to your old pressure switch as the new wiring will likely be very similar.
  6. When you purchase a new Square D pressure switch, it will come with instructions for installation. Although the general requirements for wiring are the same, it's highly recommended you fully read these instructions before attempting installation to get the most tailored information for you.



When working with electricity, it’s paramount you follow adequate safety procedures. Always check (and double check) that your power is off, wear the correct safety equipment and have someone nearby in case of an emergency.

How to Rewire A Square D Pressure Switch

For a 120-volt circuit, there will be four wires to connect. These are two line-in wires and two line-out wires — a hot and a neutral of each. A 240-volt circuit is much the same, but both of the line-in and line-out wires will be hot.

  1. Strip the wires so an inch of bare copper is exposed.
  2. Connect the wires of the same color.
  3. Twist these exposed wires using pliers.
  4. Cover the wire twist with an insulating nut.


How to Make a Square D Pressure Switch Adjustment

If your pressure switch is not broken but is not working to the best of its ability, you can perform a Square D pressure switch adjustment yourself.

  1. Take the switch cover off and you'll see a pressure adjusting nut.
  2. You can turn this clockwise to increase the pressure and anticlockwise to decrease — one full turn is about 2.5 PSI.



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