Contactor vs Relay

To turn things on and off, we need devices that are switchable by the application of a current or voltage. Electrically, we have transistors and integrated circuits. Mechanically, we have relays and contactors. The main difference between contactors and relays is the loads that they are meant to handle. Contactors are used for loads that have high voltages, high currents, or both. Contactors are used for devices that pass more than 15 amps or loads of more than 3kW. For lower amounts, ordinary relays are used.

In terms of features, a contactor has some than ties in directly with the previous difference. A contactor is equipped with arc suppression mechanisms while relays typically aren’t. At very high power loads, it is very possible that currents will arc across contacts while the switch is in transition. Arcing can cause major damage to the contact points causing it to fail much earlier than its expected lifetime. Arcing is much less likely to occur at lower voltages where relays are typically used.

Another difference between contactors and relays is the amount of power that they consume. Contactors need to switch larger contacts, thus they also have much larger electromagnets that draw significant amounts of power. In comparison, the smaller electromagnets in relays are much easier to switch and doesn’t require as much power.

The previous difference is very important when you consider that the circuitry used to decide the switching is electronic in nature. These circuits are not capable of supplying the power needed to switch contactors; on the other hand, can be switched by electronic circuits with relative ease. Because of this, relays are often used as a middleman between the electronic circuit and the contactor. The electronic circuit provides the power to turn the relay on, which in turn switches a larger voltage source needed to turn on a contactor.

Choosing between a relay and a contactor isn’t really difficult. You just need to look at your intended application. For most cases, relays can do the job without any problem. But for high power applications, using a contactor may be necessary.

Summary:

1. A contactor handles much higher current flow than relays
2. A contactor is equipped with arc suppression mechanisms while relays are not
3. A contactor draws significantly more power than relays
4. A relays is used as a middleman between electronics and a contactor

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