What is the difference between a contactor and a relay?

Forums Common electrical queries What is the difference between a contactor and a relay?


This topic contains 2 replies, has 2 voices, and was last updated by  Chezhi 1 year, 10 months ago.

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    I think I’m a bit confused between a contactor and a relay. The only difference I know between them is that a contactor is used for 3 phase circuits and a relay is used for single phase circuit. Is this difference correct or have I misunderstood?

    I would like to know the difference between a contactor and a relay.

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    Profile photo of Dnyanesh
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    Yeah,  you misunderstood Relays. First of all there are several types of relays. Few of them are mentioned below:


    1. Voltage Suppression Relays.

    2. De-Spiking Diode Relays.

    3. De-Spiking Resistor Relays.


    1. LATCHING RELAYS: This relays are also known as Impulse Relay or Electromechanical Relay. They operate under low current ratings like 5A to 20A. These relays are always kept ON as they are used for switching between different circuit paths. And this is the same relay you mentioned in your query (I guessed so).

    2. REED RELAYS: Its contacts are important so these relays are kept under inert gas.  They are well known for their switching speed.

    3. POLARIZED RELAY: These relays are used for their sensitivity property. They are too sensitive to operate even under small change in rated conditions.

    4. BUCHHOLZ RELAYS: You may well known about Buchholz relay,  if not let me introduced it to you.  These relay is used in http://Transformer to detect gas produced from oil in the oil tank. It alarms if gas is produced slow or fast than rated.

    5. OVERLOAD PROTECTION RELAYS: As name suggest they are used to protect Motors from overload current or short circuit current which can harm to winding.

    6. MERCURY WETTED RELAYS: These relays are similar to those REED RELAYS mentioned above. The only difference is its contacts are wetted in mercury instead of inert gas. These relays are used where time factor is important i.e. They operate with time.

    7. MACHINE TOOL RELAYS:  These relays are used in machine control in the industries.

    8. CONTACTOR RELAYS: This relays are famous for their heavy load operations they operates from 9A to several hundred of Amps. This relays are used for switching motors ON/OFF. They can work under 440 volts, so yes these relays are 3 phase relays as you mentioned above.

    9. SOLID STATE RELAYS: As name suggests this relays do not have any moving parts. These relays are highly reliable.

    10. SOLID STATE CONTACTOR RELAYS: These relays contain the property of both the contactor as well as solid state relays. These relays are controlled with help of PLCs, Micro processors or Micro Controllers.

    So the conclusion is there is no difference between Contactor and relay. Contactor is itself a Relay. 


    0 votes


    contactor is nothing but what you’ve  seen in starter a 3-phase supply is directly given to the contactor and then through the motor terminal…one link is present between the contactor and the motor terminal…if the link touches with the contactor motor will run(suppy flow through the terminal)..if the starter is opened the link doesn’t touch with the contactor….

    but in relay ciruit is opened when there is fault occurs


    • This reply was modified 1 year, 10 months ago by Profile photo of Dnyanesh Dnyanesh. Reason: Grammatical errors
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