What Does A Motor Overload Relay Do?

You’ll find motors at the heart of all industries, from food processing to manufacturing and everything in between. Industrial motors drive all types of machinery and equipment, including conveyor belts, sorting and packing machines, robotic arms, and more.

They are essential to the processes your business relies on but are often at risk of current overload and other issues. That’s where a relay comes in. What does a motor overload relay do? It protects a motor from damage that such overload issues can cause.

Learn more about motor overload relays in the short guide below.

What Is A Motor Overload Relay?

The humble motor is one of the most important components of industrial motor control systems. And the motor overload relay is the device designed to protect motors from overloads that damage the motor windings and cause phase failure.

Relays are essential to the industrial environment, where overload issues can lead to machinery failure, downtime, repairs, and decreased productivity. Motor overhead relays are an affordable and practical method to protect machinery from damage, reduce maintenance/repair bills, and boost efficiency.

How Does A Motor Overload Relay Work?

The motor overload relay is wired in series with the motor. When the motor is in operation, the current that flows through it flows through the relay, too.

Should that electrical current exceed the maximum recommended limit (the threshold determined by the manufacturer or industry guidelines), the relay kicks in. It interrupts the power supply and effectively stops the motor.

Most overhead relays function on an inverse time curve where the trip time decreases as the current increases. Put more simply, the more critical the overload, the faster it trips. The ‘overload trip class’ is the number that designates the time lapse ( in seconds) after reaching overload before the relay opens.

Types Of Motor Overload Relays

A conventional relay will shut the motor down when excess current is detected. But it will not necessarily detect other issues that can lead to motor failure and is a reactive solution rather than a proactive one.

Because there are different reasons and ways motors fail, there are different types of motor overload relays. The overload relays you choose depend on several criteria such as the type of motor, work environment conditions, and budget.

Thermal Overload Relays

A thermal overload relay relies on a metallic strip that will heat up and melt or bend when exposed to excessive current. This triggers the relay to trip and cut power to the motor. Thermal overload relays are typically not as accurate as electronic ones but are often more affordable.

Bimetallic

A bimetallic overload relay relies on a bimetallic strip with electro-thermal properties. This strip heats and bends when the current exceeds the predetermined threshold. When this happens, the trip contact is activated, cutting off the power supply and instantly stopping the current flow to the motor.

A bimetallic overload relay is a simple and cost-effective option but may be less accurate when it experiences extremely high temperatures.

Eutectic

In this type of relay, an eutectic alloy is housed in a tube connected to a heater winding. When current flows through the heater winding, it heats the alloy. And when the current exceeds the predetermined threshold, the alloy melts and trips the power. The relay can be reset once the eutectic alloy has cooled.

Electronic Overload Relays

An electronic overload relay monitors current for potential overload through electronic components. Electronic overload relays typically allow for adjustable trip settings. This type of relay relies solely on an electrical circuit to detect overload conditions and is often more accurate than a thermal overload relay.

Solid-State

A solid-state relay does not rely on mechanical components to work, but rather semiconductor devices like transistors. Its lack of moving parts makes it impervious to vibration which ensures a longer lifespan. This type of relay is common in industrial automation systems.

Smart

A smart overload relay is a modern version of the electronic overload relay, designed to monitor motor operation and predict potential overloads, in real-time. It does this thanks to predictive analytics of data provided via Ethernet/IP communication. Thresholds can be set according to your specific needs.

Conclusion

What does a motor overload relay do and do you really need it? Motor overload relays protect the motors they’re connected to from damaging current overloads. They save you the time and money in repairs or replacement that the motor failure would otherwise lead to.

No industrial site can operate efficiently and safely without motor overload relays. At Automation Electric & Controls, you won’t just find top-quality standard and custom control panels. We also stock motors, relays, contactors, and all the other parts you need to keep an industrial business running smoothly.

Contact us today and get what you need.