Relays and contactors are both electrically controlled switches, but they are designed for different load levels and duties.
| Feature | Relay | Magnetic contactor |
|---|---|---|
| Typical load | Control and low-power circuits | Motors and higher-power loads |
| Main contacts | Smaller | Larger and more robust |
| Arc control | Limited | Designed for frequent power switching |
| Common contacts | Multiple NO/NC combinations | Main NO poles plus auxiliary contacts |
| Typical application | Logic, alarms, interposing | Motors, pumps, HVAC, heaters |
Use a relay when
- Switching low-current control signals.
- Providing electrical isolation between control circuits.
- Adding logic contacts or interfacing with PLC outputs.
Use a contactor when
- Starting and stopping motors.
- Switching HVAC compressors, pumps or heaters.
- Handling frequent switching of higher currents.
Why both are often used together
A small relay can interface between a controller and a contactor coil, while the contactor switches the power load. Auxiliary contacts provide feedback and interlocking.
Frequently asked questions
Can a relay switch a motor?
Only small loads within its approved rating. For most motors, a properly rated contactor is the safer choice.
Does a contactor replace an overload relay?
No. The contactor switches the load; an overload relay or motor protection device provides overload protection.
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