Overload Relays

A motor is often one of the most integral components in industrial and commercial machinery. It performs a significant role in controlling automated processes and production lines. And it means you must take the proper steps to ensure the safe and reliable operation of any motor. With heat being one of the major concerns with a motor, overload relays offer an effective solution.

To find the right device for your application, RS supplies a comprehensive range of overload relays for domestic and commercial use throughout North America. We're committed to offering the highest quality motor overload protection products available. Choose from renowned manufacturers such as ABB, Schneider Electric, Siemens, and more – all available to order now.

What are overload relays?

An overload relay – sometimes called a contactor overload relay – is an electromechanical device that protects motors from an overload or overheating. This can happen when the motor draws or uses too much current. The result can be a buildup of heat, which can damage the motor and its windings. With an overload relay, however, this can be prevented to ensure continued operation.

The different types of overload relays

Not all overload relays operate in the same way – though each type will still deliver valuable and much-needed protection for your motor(s). The first type that we can provide are called thermal overload relays and incorporate bi-metallic strips. If the current is resulting in overheating, both strips expand and open the contact to interrupt the power supply to the motor.

Unlike thermal overload relays, the electronic variant doesn't include bi-metallic strips to protect the motor. Instead, this type of motor overload protection uses sensors or transformers to work out how much current is being passed through to the motor. When this amount is too much, the relay will then trip the circuit and stop the motor.

How does an overload relay work?

For overload relays to offer protection, they must be wired in series with the motor. When the current flows to the motor, this configuration means it must also first pass through the relay. If the amount of current reaches an excessive level, the relay will trip. This will break the circuit – stopping power from reaching the motor until the relay is reset or the problem resolved.

Each contactor, electrical or thermal overload relay can be determined by their "class". This is a number that shows how long in seconds the relay takes to trip. The three most common classes available are 10, 20, and 30 – though there is also a Class 5 option for specific applications. The NEEMA Standard MG-1 defines these classes, which trip at 600% of motor full load amps (FLA).

In addition, motor overload settings should be set at 125% of a motor's full-load current. Some of the leading manufacturers that we stock build this into their relays as standard. Otherwise, it can be set at the motor's nameplate current plus 25%

Motor overload protection: Why is it important?

Motor overload protection is essential to ensure the safe, reliable, and long-lasting operation of machinery and equipment that include an electric motor. An overload relay stops a motor from overheating, which can cause damage to the controller, motor, or branch circuit conductors.

An overload relay can also reduce the risk of severe failures that result in electrical fire.

Do you still need a circuit breaker when using an overload relay?

Yes – it is important to use both an overload relay and a circuit breaker where an electric motor is used. The relay is designed to provide motor overload protection if overheating occurs. But it isn't designed to protect the circuit itself if too much current is passing through. This is why you need to use a circuit breaker or fuse too.

Overload Relays: Uses and applications

Electric motors are now commonly found in many different modern machines and equipment. It means that overload relays can have various domestic and commercial uses and applications.

In most – if not all cases – the role of the overload relay is the same: to protect the motor from overloading and overheating. If this occurs, the relay then deactivates the motor until the issue can be resolved. Some overload relays can also be developed into microprocessor systems.

Industries where motor overload relays feature include:

• Construction and civil engineering
• Assembly lines and production
• Heating, ventilation, and air conditioning
• Production lines and machinery
• Craftmanship: Metal, plastic, or woodwork

Why you can trust RS for your overload relays

Overload relays are a critical component in the care and protection of electric motors. So, you'll need to be completely satisfied with your product choice. It makes all the difference in terms of the safety and reliability of your equipment. At RS, we're committed to supplying the very best motor overload protection products and offer an extensive range to choose from.

As the largest authorized distributor in North America, we stock all the leading manufacturers – from ABB and Siemens, to Eaton and Schneider Electric. You can also refine your search further by using the filters on this page. It's a fast and convenient way to find the exact overload relay you need. Filters include required power rating, control voltage, terminal type, and more.

Of course, there's also the option to locate the motor overload protection you need by entering the product name and/or number in our search bar if you've already made your choice.

If you would benefit from additional assistance when it comes to overload relays, please get in touch with our friendly team. We're here to answer any questions you have about the products we supply. We also offer a free expert content hub. It's full of articles designed to provide you with any support or advice you need to get the most out of your RS purchases.