Contactors vs Relays: Uses & Differences

Ed Combs
By Ed Combs
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Electrical contactor vs relay: do you know the differences? There is much confusion around these two components, which are often (mistakenly) referred to interchangeably in the electrical industry. Although electrical contactors and relays are both essential components of modern electrical systems that help control electrical current flow, significant differences between the two devices can impact their suitability for specific applications. 

In today’s post, we are clearing up any lingering confusion around the two by examining each component separately, followed by more in-depth details about how the relay vs contactor function differently within electrical applications.

Electrical Relays

Let’s begin with the electrical relay, which is used to control contacts of an electrical circuit when there is a change of parameters or conditions in the same circuit or any other associated circuit. The electrical relay plays a critical role in controlling and safeguarding circuits, and it is commonly used in single-phase applications with low-voltage control circuits, such as household appliances, traffic signal lights, and HVAC systems.

What is an Electrical Relay?

An electrical relay is a switch that can be turned on or off with a low voltage and used to control multiple circuits. Relays allow complete electrical isolation between the power (supply) circuit and the control circuit and can be used to switch large electrical loads by only using a small electrical current.

Electrical relays feature a coil that creates a magnetic field and contacts that open and close the circuit. Some relays also have additional features, such as diodes or resistors, that help protect the switch from voltage spikes.

Electrical Relay Uses

Electrical relays are used for a variety of reasons, including controlling large electrical loads with a small level of current, creating electrical isolation, or controlling more than one electrical circuit using one supply. Relays can be used in everyday applications as well as industrial applications.

For example, as mentioned earlier, you can find electrical relays in action in everyday applications, such as traffic lights, air conditioning systems, household appliances (washing machines, dishwashers, etc.), cars, or computers.

In industrial applications, relays are used with safety circuits (safety relays), motor control, temperature control systems, circuit protection such as short circuits, overvoltages, and under voltages, and control circuits. For example, a small electrical current can be used to control the larger electrical load of a motor during operation by incorporating a relay with push buttons that start or stop machinery or conveyor belts.

Electrical Contactors

Like relays, the electrical contactor separates the control circuit from all main circuits with higher power ratings and repeatedly establishes and interrupts the electric circuit under normal conditions, i.e., an electronic switch.

What is an Electrical Contactor?

Electrical contactors are electromechanical control devices used to make or break the connection between the load and power supply - again, similar to electrical relays. However, a contactor is used for applications or in circuits that require more current.

A contactor is comprised of three main components, including a coil, enclosure or frame, and contacts. Basically, when a control circuit is powered, the electromagnetic coils of the contactor get energized and pull the connector, which closes the main circuit - and power flows through the contactor.

Electrical Contactor Uses

Contactors are used for a number of different applications across a range of industries. Some applications include an electrical motor starter, lighting control, evaporator control, capacitor banks, or heating systems.

Main Differences Between Relays and Contactors

Although operationally, both devices help control electrical current flow, the contactor vs relay difference includes specific distinctions between the features and the application, making one or the other more suitable in certain circumstances. Let’s review.

Load Capacity

When it comes to an electrical contactor vs relay, the load-carrying capacities are very different, as contactors have a much greater load-carrying capacity. Although both include three ratings, i.e., voltage, ampere, and horsepower, these ratings will be higher in a contactor than a relay.

For example, the electrical relays typically have an ampere rating of less than 10 A and a horsepower rating of less than 0.5 HP. However, electrical contactors are rated for higher amperes and horsepower. In the case of voltage ratings, relays are generally less than 250 V, and contactors are up to 1000 V.

Symbols

The electrical symbols for these devices are also different, as you can see by the diagram below.

AC/DC Loads

Although an electrical relay works well for both AC (alternating current) and DC (direct current) power when the horsepower and amperage ratings are suitable, the electrical contactor is better suited for AC power than DC because the large inductive loads on typical contactors can generate dangerous reverse ‘flyback’ arcs.

Open/Closed Contact Standards

Electrical contactors are typically designed to operate with normally open (NO) contacts, which means the main circuit is open when the control circuit is not powered and closes when the control circuit is powered. Therefore, the main circuits will always open and load operation will halt during a control power failure.

On the other hand, electrical relays can be both Normally Open (NO) or Normally Closed (NC), depending on the function the application requires. With NO relays, the main circuit is open when the control circuit is not energized and closes when the control circuit is energized or powered. Alternatively, with NC relays, the main circuit is closed when the control circuit is not energized and opens when the control circuit is powered.

Multiple Circuits

Typically, electrical contactors are only used to control a single main load circuit, either 1-phase or 3-phase. However, while electrical relays can also control a single main circuit, they can also be used to control multiple main circuits by relaying information to each.

Auxiliary Contacts

Another contactor vs relay difference is auxiliary contacts. Whereas electrical contactors have auxiliary contacts to verify the operation of three-phase power input and output circuits, electrical relays typically do not have auxiliary contacts since they are most often used with smaller power circuits.

Physical Size

Electrical contactors are larger in size than relays because they have to accommodate multiple phases at a higher power rating, as well as space for the necessary additional safety and auxiliary features (which are explained next).

Safety Features

Since electrical contactors operate with a larger power rating, there are chances for electric arc formation during switching. Therefore, contactors typically include built-in ‘arc chutes’ for suppressing this formation.

Multi-Phase

Contactors are compatible with both three-phase and single-phase circuits, but they are used most often in three-phase circuits - perhaps because relays only support single-phase circuits. If no contactors are available and relays have to be used in a three-phase circuit, then three main relay contacts will be required, i.e., one for each phase. However, this makes the wiring cumbersome and the circuit more complex. Furthermore, the maximum power ratings must always be observed.

Choosing Contactors and Relays for Your Needs

Although both the contactor and the relay have the same core functionality in modern electrical systems, their significant differences can impact their suitability for specific applications. Hopefully, this information has helped to better understand the distinctions between these two devices to make choosing the right one for your needs much easier. 

Generally, contactors are applicable for 9 A or more current, up to 1000 VAC, and 1 or 3 phase circuits. For relays, however, the general rules of thumb are 10 A or less current, up to 250VAC, and 1 phase circuits.

The function and application needed for the system are also critical in deciding which component to use. Basically, electrical relays are more common with control automation and protection circuits, and electrical contactors are commonly used for switching high-power equipment like motors, lights, and capacitors. 

No matter which component is needed, you can find a wide variety of both contactors and relays in stock at Peerless Electronics. We are the largest stocking distributor for leading manufacturers of these devices - and our custom-tailored technical support and numerous other value-add services back every purchase.  Conveniently shop for the components you need online at Peerless Electronics website today!

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