Difference between Contactor and Relay

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When browsing catalogues and online stores and comparing product specifications, it is not always clear what the difference between contactor and relay is.

First, what contactors and relays have in common

In fact, contactors and relays are two closely related terms. Both of them are electrically operated switches used for control and switching of loads. Also, they are constructed in a similar way: 1) both have an external envelope to protect all the internal parts from the external environment 2) an electromagnetic coil is provided for opening and closing of contacts and 3) the contacts in these devices are opened and closed by exciting this electromagnetic coil.

Now, difference between contactor and relay

However, on the one hand, a contactor is used for switching of motors, capacitors, lights and other devices that drain very high current. It has at least a single pair of three phase input and output contacts.

Difference between Contactor and Relay
Example of Schneider Electric magnetic contactor

Furthermore, some contactors come with additional auxiliary contacts that may be either NO or NC. These auxiliary contacts get activated along with the main contacts. Switching is achieved by energization and de-energization of the contactor coils. Contactors are also chosen upon the ampere ratings of the load and require an additional supply (either AC or DC depending upon the type of contactor we use) for excitation. Finally, they are used for power switching and are usually open.

difference between contactor and relay
Example of power relay from Schneider Electric

On the other hand, a relay consists of at least two contacts and an excitation coil. These contacts may be open or closed and they become closed or opened by exciting the coil. Moreover, relays are usually used for switching of control circuits and cannot be used for power switching with relatively higher ampacity. Instead, they can be used for switching of small lights, sirens, indication lamps and others.

For a more graphic representation of the difference between contactor and relay, please refer to the table below

Relay

Contactor

  • Relatively smaller in size
  • Larger when compared to relays
  • Used in circuits with lower ampacity. (Max 20A)
  • Used in circuits with low and higher ampacity up to 12500A
  • Mainly used in control and automation circuits, protection circuits and for switching small electronic circuits.
  • Used in the switching of motors, capacitors, lights etc.
  • Consists of at least two NO/NC contacts
  • Consists of a minimum one set of three phase power contacts and in some cases additional auxiliary contacts are also provided.

In other words, contactors work in much the same way as relays do. The working principle of contactors and relays is the same; however, contactors can handle much larger currents, they are usually bulkier than relays, and they could be specially designed to work with 3-phase AC currents.

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Explanations courtesy of Electrical Classroom and Pediaa