Contactor or Motor Starter – What is the Difference?

Making choices in a contactor or motor starter

Its a question we hear often – “Is it a contactor or motor starter”? This question is understandable since contactors and starters both control electric motors and many people use the two terms interchangeably, which can lead to a little confusion. The mechanical elements of starters and contactors are identical. Coil, contacts, arc chutes…and both devices typically use a lower control voltage to electromagnetically pull contacts together. So what’s the difference? It’s simple.

A contactor is really just an overgrown relay. It is but one component of a starter and is rated by voltage. The contactor applies voltage to a contactor coil to close the contacts and to supply and interrupt power to the circuit.

A motor starter is simply a contactor PLUS an overload relay and is rated by motor HP or amperage. If there is no overload relay it is not a starter any longer. It’s back to being just a contactor. The starter employs overload relays to protect the motor from load surges by shutting it down to prevent overheating. The term ‘motor starter’ usually refers to the complete assembly. This includes but is not limited to: the enclosure, contactor, control transformer (if any), overloads and fuses (if any).

Making choices in a contactor or motor starter

Contactors and motor starters are available with either NEMA or IEC ratings.