Contactors and relays both use an electromagnetic coil to open and close electrical contacts, but they serve different roles in a control circuit. A contactor is built to switch higher current loads directly to motors and other heavy equipment, with contacts rated for the repeated switching and inrush current that motor starting demands. A relay, by contrast, typically handles lower-current signaling and control functions, often used to isolate a control circuit from a separate power circuit or to add logic between sensors and larger switching devices like contactors. Because contactors and relays are foundational to most motor control panels, they’re closely related to other components in our electric motor starters line, where a contactor is typically paired with an overload relay to form a complete starter assembly. 3BG Supply Co. stocks contactors and relays across a range of coil voltages and current ratings for industrial control panel repairs and new builds.
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FAQs
What is the difference between a contactor and a relay?
A contactor is designed to switch higher current loads, typically to motors and other heavy equipment, with contacts built to handle repeated switching and motor inrush current. A relay generally handles lower-current control and signaling functions, often used to isolate circuits or add logic between smaller components.
How does a contactor work?
A contactor uses an electromagnetic coil that, when energized, pulls a set of contacts closed to complete a circuit to the connected load. When the coil is de-energized, a spring returns the contacts to their open position, disconnecting power.
What role do contactors play in a motor starter?
In a motor starter, a contactor provides the switching function that connects and disconnects power to the motor, while a paired overload relay monitors current draw and opens the control circuit if the motor is overloaded. Together, they form the core components of a combination motor starter.
How do I select the right coil voltage for a contactor or relay?
The coil voltage needs to match the control circuit voltage that will energize it, which is often lower than the load voltage the contactor switches — for example, a contactor might switch 480V power to a motor while its coil operates on 120V control voltage. Check your control panel's schematic or the existing component's nameplate to confirm the correct coil voltage.
What causes contactors and relays to fail?
Common failure causes include contact pitting or welding from repeated switching and inrush current, coil burnout from overvoltage or continuous duty beyond its rating, and mechanical wear in the moving armature assembly. Regular inspection for contact wear, unusual chattering, and coil overheating helps catch failures before they take down connected equipment.
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