What is the Difference Between Relay vs Contactor

Relay vs contactor – If we are working in the industry sector especially in the utility or maintenance division related to machines and electricity, we will find a lot of relay and contactor. Even though those two have different names, it still confuses people the difference contactors vs relays. Let us read the explanation below to clear this confusing matter.

What is the Difference Between Relay vs Contactor

Both relays and contactors are operated by electrical switches controlled by the coil. When the coil is energized when we apply voltage to it, the NO contact can change into NC contact and vice versa.

Even contactors and relays have the same working principle, they are different electrical switches. While both of them control and switch loads in the circuit, they have basic differences between contactor and relay. We will find their differences in load capacity, safety plan, application, current rating, and many more.

In short,

Electrical relay is a device that has contacts to control a circuit using the same circuit or separated circuit operated by a change of condition (coil).

Electrical contactor is a device to establish or interrupt an electrical circuit under normal and specific conditions.

The brief explanation above does not help much analyzing the differences between relays and contactors. Hence, let us continue to the next section.

relay vs contactor

Relay vs Contactor: Types of Device

Electrical switching is necessary for controlling electrical circuits. Its automation and fast switching can accurately open and close circuits when condition is met. Of course we don’t have to get panicked everytime we need to switch the contact, leave that matter to the relay or contactor.

Other things we need to give attention is the power of the circuit. Of course we want to use the best switches for our purpose, either relay or contactor.

Since the relay has a smaller coil, contact, and other components, we use this when we are dealing with a low power device.

Contactor has larger components so it is suitable for high power device.

Relay vs Contactor: Load Rating

Both relay and contactor have different load ratings on them. Load rating is connected to their respective current rating.

Relay is suitable for low power circuits with maximum current rating 10A or less.

Contactor is suitable for high power circuits with current rating 10A or more.

Relay vs Contactor: Contacts

Both relay and contactor have the same NO and NC contacts but their application depends on their purpose in controlling the circuit.

Relay is often used for NO and NC evenly for many applications. When the coil is not energized, it still can be connected again. Relay can be NO and NC depends on its purpose.

Contactor is often used with NO contact (form a contact). When the coil is not energized, the connection in the circuit is lost. Contactor has the majority of NO contact to disconnect the circuit when the coil is not energized.

Relay vs Contactor: Auxiliary Contacts

Auxiliary contacts are used to provide additional contact for the main contact. It is used to provide additional NO or NC contacts to perform a specific sequence operation.

Relay doesn’t have auxiliary contacts since it contains multiple NO and NC combinations for a single relay. We can use every combination to make complex commands.

Contactors are often equipped with auxiliary contacts NO or NC which serve another purpose in the circuit. The example of this auxiliary contact is controlling the break or start motor while the main contact delivers the current to the motor.

Relay vs Contactor: Safety Plan

Safety plan on relay and contactor is crucial to protect the circuit if something severe happens, like overloads, voltage or current in the circuit exceed the limit, or broken components.

Because relays are used for low power circuits and it has spring to pull the contact when the coil is not energized, safety plans are not really needed.

On the other hand, contactors are used in high power circuits so safety plans are a must. It is often to use spring-loaded contact to cut the circuit when the coil is de-energized. It is a dangerous situation if the circuit is energized when it is supposed to be off.

Relay vs Contactor: Arc Suppression

High power circuits often produce sparks when the circuit is energized or de-energized. Arc suppression is used to lengthen the arc travel path to suppress the arc.

Relays which are operated for low power circuits do not produce big sparks or even not at all.

Contactors on the other hand are operated for high power circuits which produces sparks when its contact is switching.

Relay vs Contactor: Overload Safety Plan

Overload safety plan is designed to minimize damage and protect the circuit when the load inside a circuit exceeds the limit.

Relays have low risk from overload incidents so it is common to not use overload safety plans.

Contactors are connected to overload that will disrupt the circuit if the current exceeds the maximum current rating for a period time (10-30 seconds). It is connected to ensure equipment safety when the current is too high.

Relay vs Contactor: Size

The physical size of relay and contactor depend on their components.

Relay has smaller components so its overall size is smaller than a contactor.

Contactor has bigger components so its overall size is larger than relay.

Relay vs Contactor: Switching Speed

Switching speed is important for controlling circuits, even a second is crucial to connect or disconnect the current path.

Relay can switch contacts much faster than a contactor.

Contactor can switch contacts much slower than relay.

Relay vs Contactor: Connection

Not only NO and NC connection, both relay and contactor are connected to additional points to serve specific purposes.

Relay has a common contact to connect to the neutral point.

Contactor is connected to the overload to interrupt the circuit if the power surpassed the limit.

Relay vs Contactor: Power Consumption

When designing relay and contactor control circuits, we need to calculate their power consumption first, to make sure they can be operated very well.

Relay has small electromagnet components that consume smaller power.

Contactor has large electromagnet components that consume higher power.

Relay vs Contactor: Application and Voltage Rating

Just like load rating, both relay and contactor have maximum voltage rating. This will give us help when choosing between relay or contactor and make sure we use the best one. 

Relays are mainly used for single phase circuit application. Relays are commonly rated up to 250V.

Contactors are mainly used for three phase circuit application. Contactors are commonly rated up to 1000V.

Relay vs Contactor: Functions

Because the load rating, voltage rating, and switching speed, both relay and contactor serve different functions.

Relay is mainly used for signal transmission, conversion, control and automation circuit, protection and small switching electronic circuit, and detection. Its operating current in the circuit is low. It is commonly used to control low signal in the circuit.

Contactor is mainly used to connect or disconnect the main circuit where the current is higher than the control circuit and switching power circuit (transformer, motor starter, capacitor bank).

Relay vs Contactor: Cost

Cost is one of the basic decision makers when designing a control circuit. We don’t want to use inefficient components to build a circuit. It is obvious that:

Relay has less cost.

Contactor has more cost.

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