Electro Mechanical Assembly Debate – Relay Vs. Contactor

Today, solid state components and logic circuits are replacing some of the standard electro mechanical assembly devices. However, there is still a need for important parts (like contactors and relays) in control circuits and industrial applications. Yet, many people confuse these two components and believe the terms are interchangeable. The truth is, although they are similar there are major differences that anyone interested in electronics or industrial control circuits should be aware of. Here are ways you can easily tell the difference.


Did you ever watch a relay race? One runner starts out with a baton and passes it to another one, and this may happen several times until the final runner reaches the finish line. This kind of race takes cooperation and working together to win. Electromechanical relays use electric energy instead of batons.

A relay is an electro mechanical assembly that uses a coil of wire to create electromagnetic energy that opens and closes a set of contacts. For example, a normally open (NO) relay has a set of contacts separated by the force of a spring. When they become magnetized (from the flow of electric current), they are attracted together, and this closes the circuit. Once power is removed the spring separates them, and the circuit opens.


A contactor is an electro mechanical assembly that works on the same principles as relays. So what’s the difference? Relays work within control circuits and are used to transfer control circuit power (usually not more than 120 volts AC). Contactors (like an AC compressor contactor) are used to switch high voltages for heavy machinery and are connected directly to motor and compressor power circuits.

Things to Remember

So you don’t confuse the terms, think of relays as low voltage control circuit devices and contactors as high voltage switches. This should help to clear up some of the confusion.


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