Difference Between Relay and Contactor

By May 26, 2020Article

There is a lot of confusion around the industry about the difference between contactors and relays.

Relays are used to control contacts of an electrical circuit due to a change of parameters or conditions in the same circuit or any other associated circuit.

Contactors, on the other hand, are used to interrupt or establish connections in an electrical circuit repeatedly under different conditions.

A relay is a type of electromagnetic switch which is operated based on the current change in a circuit. When an overload condition is detected in a circuit, it will trigger the electromagnetic armature of the relay to close or open depending on the configuration.

The operating principle of the contactor is similar to the relay; the current flowing through the contactor energizes the electromagnet. When an overload is detected in the electrical circuit, the energized electromagnet then creates a magnetic field. This causes the core of the contactor to move the armature to an open position, thus cutting the flow of power in the circuit.

Comparison between Relays and Contactors

There are several differences among relays and contactors, however, some basic and common differences among them are discussed below.

1. Load Capacity

The first difference among a relay and contactor is that both have different load capacities. Relays are used with electrical loads at a range of about 10 amperes or less, while a contactor load capacity is greater than 10 ampere. 

2.Open/Closed Contact Standards

The second difference is that relays are designed to operate in both ways i.e. in normally open or normally closed as per function demand.

While contactors are designed to operate in a normally open configuration. This can be summarized as when the contactor is triggered there is no connection of contactor with circuit while a relay can have a connection or not have a connection with circuit when triggered as per the configuration of the relay in a circuit. 

3.Auxiliary Contacts

In contactors, auxiliary contacts are used to perform a different function that is linked to controlling the contactor. Auxiliary contacts for a contactor can be normally open or normally closed as per requirement.

4.Safety Features

The safety features in relays and contactors are different as per the power of each device. Spring-loaded contacts are used to ensure that the circuit is tripped or opened in case of any over-circuit condition to reduce or prevent damage to electrical devices. Relays are used in circuits that have load capacity equal to or smaller than 10 amperes, so spring load contacts are not commonly seen in relays due to their low load capacity.

On the other hand, contactors have load capacities greater than 10 amperes which means that they can carry higher loads. As higher loads are carried by contactors, spring-loaded contacts are used to ensure the circuit is broken when it is de-energized due to an overload condition. In circuits that have higher loads, the contacts of contactors are welded together, and it can result in a dangerous scenario as in case of an overload condition the circuit will not be opened to eliminate this scenario spring-loaded contacts are using.

Applications of Relay and Contactors

Relays are developed to be used in various single-phase networks thus they have single-phase applications while the contactors are developed to be used in three-phase networks. Different kinds of relays are used in different circuits for different applications while some conventional applications of relays are:

  • Automotive Applications
  • Motor Control
  • Industrial Applications
  • Controlling Power Loads

Contactors have also different categories and while there are numerous applications of contactors, some common applications are listed below:

  • Motor Starters
  • Capacitor Banks Switching
  • Lighting Control
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