Contactor wiring diagram

Motor: on

Open the control and watch the power contact spring open with the coil — a milliamp of control current drops tens of amps of load. That separation is the whole reason a contactor exists. The copper highlight is the live path, not a wire colour.

A contactor lets a small control current switch a large load: the coil is an electromagnet, and energizing it pulls the power contacts closed. Here a maintained control switch feeds the coil; the coil pulls the power contact shut and the motor runs. Open the control and the contact springs open with the coil.

How this circuit works

There are two separate circuits sharing one device. The control circuit is the small one: a switch feeding the coil. The power circuit is the big one: the supply, the power contact, and the motor. They are electrically apart — the only thing linking them is the mechanical pull of the coil on the contact. Close the control switch and the coil energizes; the moment it does, it drags the power contact closed and the motor gets its supply.

Take the control away and it all lets go at once — coil de-energizes, spring opens the contact, motor stops. That clean separation between a light control signal and a heavy load is the entire reason contactors exist. A real one gangs three power poles for a three-phase motor; this is that same coil-and-contact trick, shown once.

Questions people ask

What is the difference between a contactor and a relay?

Same idea, different scale. Both use a coil to pull contacts closed. A relay switches small control or signal loads; a contactor is built for the heavy power contacts and arc suppression that switching a motor or a bank of heaters demands. When people say contactor they mean the big one.

Why switch a big load with a small coil?

So the thing you press, or the thermostat that closes, only has to handle a trickle of coil current, while the tens of amps go through robust power contacts nearby. It keeps the control wiring small and safe, and it lets a low-voltage or remote signal command a large load.

What happens when the coil loses power?

A spring pulls the contacts open again the instant the coil de-energizes. Open the control switch in the diagram and the power contact springs open with the coil, and the motor stops. There is no memory here — no power to the coil means open contacts.

Motor start/stop station — add a seal-in and pushbuttons.
Occupancy sensor wiring — another small signal commanding a load.
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