How to Wire a Contactor

A guide to safely routing and connecting electrical wires to a contactor

Co-authored by Ricardo Mitchell

Last Updated: June 7, 2024

Many large pieces of equipment are powered directly from high voltage lines. These lines far exceed the 120 volts AC standard in most homes. 240 volts AC and 480 volts AC are commonly used for these large pieces of equipment, such as motors, industrial machines, and large household appliances like washers and dryers. These voltages must be electrically isolated from the standard 120 volts AC. Contactors are used to provide this isolation. Contactors use 120 volt standard power to energize a magnetic coil, which causes a set of internal contacts to close and provide higher power to the equipment. Use these tips to learn how to wire a contactor.

How to Do Contactor Wiring

Look over the contactor manufacturer information to identify the input and output pins.
Determine if the contactor has an auxiliary output contact.
Strip the wires.
Run all input and output wires to the contactor.

Steps

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Make sure that the contacts of the contactor are rated in both voltage and current to handle the expected load that will be required by the equipment being powered. Contactors are available from building and construction supply stores, as well as some larger hardware stores.
The manufacturer information will identify the 2 input pins for 120 volts AC control. The may be 2 or more sets of output contacts identified. These contacts may be indicated on the label as normally open (NO) and normally closed (NC). These contacts also may be shown as a drawing of a line from 1 contact ending in a dot (the NC contact) and another line from another contact that is near the dot, but does not touch the dot (the NO contact.)^{[1]
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Expert Source

Ricardo Mitchell
Electrician, CN Coterie

Expert Interview. 6 May 2020.}

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Some contactors provide an auxiliary output contact as a signal to the isolated part of the circuit that the contactor has been energized. This auxiliary contact will not be rated at the higher voltage. Instead, it should be rated at 120 volts AC.
Remove all power to the wires. Run all input and output wires to the contactor. These wires should be rated in the manufacturer information. Use wire strippers to cut excess length off of the ends of the wire, making sure that the wires are long enough to reach the intended contact. Wire strippers are available at hardware stores and electric supply stores.
Use the wire strippers to strip a half inch (13 mm) from the ends of each wire. If the wire is stranded, twist the exposed wire to ensure that no strands are left hanging. Stray strands may make unintended contact with a piece of the equipment and cause damage.
Use a screwdriver to loosen the holding screws in the contact blocks for the wires. Insert the wires only so far that no insulation is pushed into the contact area of the block. Make sure that no stray strands are jutting out from the contact block. Tighten the screws on the contact blocks.
Apply the control voltage to the input. Listen for the contactor to click as it engages. De-energize the contactor.
Put the stripped end of each wire into the appropriate contact block after loosening the screw of the block. Make sure that no stray strands of wire are jutting from the contact blocks. Tighten down the screws of the contact blocks.

Expert Q&A

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Question

My contactor doesn't really match up with the illustrations? Will this still work?

Ricardo Mitchell
Electrician & Construction Professional, CN Coterie
Ricardo Mitchell is the CEO of CN Coterie, a fully licensed and insured Lead EPA (Environmental Protection Agency) Certified construction company located in Manhattan, New York. CN Coterie specializes in full home renovation, electrical, plumbing, carpentry, cabinetry, furniture restoration, OATH/ECB (Office of Administrative Trials and Hearings/Environmental Control Board) violations removal, and DOB (Department of Buildings) violations removal. Ricardo has over 10 years of electrical and construction experience and his partners have over 30 years of relevant experience.

Ricardo Mitchell

Electrician & Construction Professional, CN Coterie

Expert Answer

There are all different kinds of contactors out there, and they're all wired differently. Consult the diagram that came with your contactor and follow their instructions.

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Question

What are the letters on the conductor?

Ricardo Mitchell
Electrician & Construction Professional, CN Coterie
Ricardo Mitchell is the CEO of CN Coterie, a fully licensed and insured Lead EPA (Environmental Protection Agency) Certified construction company located in Manhattan, New York. CN Coterie specializes in full home renovation, electrical, plumbing, carpentry, cabinetry, furniture restoration, OATH/ECB (Office of Administrative Trials and Hearings/Environmental Control Board) violations removal, and DOB (Department of Buildings) violations removal. Ricardo has over 10 years of electrical and construction experience and his partners have over 30 years of relevant experience.

Ricardo Mitchell

Electrician & Construction Professional, CN Coterie

Expert Answer

Most conductors label the terminals with letters like L, N, E, A1, A2, L, and P. Those correspond with the letters on the diagram that came with your contactor. It should make it a lot easier to wire everything together.

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What does 'loop' mean?

Community Answer

A loop is a fastener consisting of a ring that protects the inside surface of a small hole.

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Warnings

All voltages used for a contactor, including the 120 volts AC control voltage, are potentially fatal. Make sure that all power is turned off before any work is done on a contactor.

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