How to Install a Definite Purpose Contactor

John DeMerceau

A definite purpose contactor is an automatic electrical control device that switches power on whenever it is necessary to start a motor to which it is connected. For example, a definite purpose contactor installed on an air conditioner would respond to an electrical signal that your thermostat sends to turn on the air conditioner motor as soon as your home reaches a certain temperature. These automatic switches, which are also used for controlling swimming pool heaters and filters as well as for industrial use, are easy to install. However, proper wiring procedure must be followed to avoid any safety hazards.

A definite purpose contactor is part of your air conditioning system.

Step 1

Turn off the power to the device or motor for which you are installing a definite purpose contactor. Turn off the circuit breaker for the line that supplies power to the device or motor, if possible. Disconnect the power and motor leads of any existing control switch.

Step 2

Locate an appropriate mounting surface, such as a post or junction box, near the motor to which you want to connect the definite purpose contactor.

Step 3

Position the contactor vertically against the mounting surface, Mark all mounting holes with a marker or grease pencil.

Step 4

Drill pilot holes at the marked points, using a bit that is thinner than your mounting screws. Install anchors in soft wood as necessary.

Step 5

Attach the contactor to the mounting surface with screws. Use nuts behind a metal mounting plate or surface and tighten them by grasping each nut with a wrench as you tighten each screw with a screwdriver.

Step 6

Check the wiring diagram supplied by the contactor manufacturer to determine which set of terminals to connect to the motor. For instance, the pair of terminals on the top or on one side could be the motor terminals.

Step 7

Strip about one-quarter of an inch of insulation off of each end of a cable that is a few inches longer than the distance between the contactor and your motor. Strip about one-eighth of an inch of wire from each of the strands of wire in the cable.

Step 8

Loosen the correct terminal screws on the contactor and either wrap the exposed ends of the wires around the screws or insert them into the quick-connect terminals if your model of contactor has such connectors. Tighten the screws once you securely connect the wire to the terminals.

Step 9

Connect the other end of the wires to the terminals of your motor.

Step 10

Locate the power terminals of your contactor. Prepare a length of cable that is long enough to comfortably connect the contactor to the power source by stripping the insulation according to the instructions in Step 7.

Step 11

Connect the exposed end of the wires on one end of the cable to the proper terminals on the contactor and the other end to the terminals of your power source.

Step 12

Use any remaining terminals to connect accessories to your contactor as necessary.

Step 13

Turn your power on and start your motor or device. Test it as recommended by the manufacturer to make sure it works properly.