Main Differences between a Relay and a Contactor

by Stephen Ellison
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Without a doubt, there is confusion when it comes to stating the noticeable differences between contactors and relays. All too often, the two terms are used interchangeably. The defining differences are often not apparent to users of contactors, especially. In this article, you will find relevant answers to your questions.

According to experts at the prestigious Institute of Electrical Engineers, a relay is referred to as a device with a single contact circuit, which is often operated by a viable change in the conditions within the same circuit or other associated units.

A contactor, on the other hand, refers to a device used repeatedly to establish and interrupt an electric circuit in the normal conditions.

What are the unique features between contactors and relays?

There are unique textbook definitions that seem to be similar enough, even though not so helpful.  From these excerpts, both devices perform the same task, which entails switching the circuit.

So, what really is the difference really?

The load capacity

A relay is generally classified as a device that can carry a load of about 10A. On the other hand, a contactor is defined as a device that can carry a rather higher load than the standard 10A.

While this definition may look simple, it gives an accurate picture of the picture ultimately.

At the same time, it does not capture the standards and physical differences of the devices like in the next paragraph.  

Auxiliary contacts

For those who feel a bit confused about the operating mechanisms of a contactor, the device is often fitted using an auxiliary contact, which may be NO or NC.

But these are often utilized in performing various additional functions that are related to the control of the contactor.

For instance, the DC contactor can transmit power to a motor, even though the auxiliary contact is situated in the motor’s control circuit.

Safety Features- The Spring-Loaded Contacts

The arc suppression is another safety feature found in multiple contactor types. Magnetic arc suppression extends the path a DC contactor’s arc is suppressed.

Because relays are not tailored for high loads, the arcing is not really a concern. So the suppression is somewhat less common on these relays.

Safety Features- Overloads

Contactors are most of the time linked to overloads, which can interfere with the operations of the circuit precisely if the currents exceed a threshold for some time.

This plays a significant role in protecting the downstream of the equipment from damage. On the contrary, relays do not have overloads.

Applications of Relays vs. Contactors

When it comes to their applications, contactors are built and then used in about 3-phase applications. Relays, on the other hand, are commonly used in 1-phase applications.

A contactor will join two poles without a circuit in between. A relay comes with a common contact which connects to the neutral position. Besides, contactors are rated for about 1000V. 

On the other hand, relays are rated to about 250V only.

Final Thoughts

In practice, you need to look at the functionalities of the two devices too. For circuits with an overload condition, a contactor could be the best option. In cases where there is a need for lower switching to power, then a relay is more of an economical choice.

 

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