In the electrical industry, overload relays play a crucial role in safeguarding motors from potential damage by managing risks associated with phase failure, excessive temperatures, and electrical overloads.
Typically installed in series with a contactor or switching device, these relays are vital for preventing issues that arise when a motor draws excessive current, which can lead to overheating and damage to its windings. Ensuring the protection of motors is essential for maintaining efficient and safe operations in various applications.
Understanding Overload Relay Types
There are distinct types of overload relays available, each designed to function optimally under specific conditions. The choice between different relay designs greatly influences the efficacy of motor overload protection. Overload relays are generally categorized into two main types: bimetallic and solid-state (or electronic) overload relays.
The bimetallic overload relay, also known as a thermal overload relay, operates by cutting power when prolonged excessive current is detected. As a more cost-effective option, it utilizes a bimetallic strip and heating element, which can lead to less accuracy, especially at elevated temperatures.
Conversely, solid-state or electronic overload relays offer greater precision as they rely solely on an electrical circuit to identify overloads, eliminating the need for a bimetallic component.
Choosing the Right Overload Trip Class
Class 20 is fitting for general-purpose applications, balancing protection with reduced maintenance needs
For effective motor overload protection, it is vital to match the motor with an appropriate overload relay trip class. Overload relays typically operate on an inverse time curve, where the tripping time decreases as the current increases. This timing is represented by the overload trip class, indicating the seconds it takes for the relay to activate once an overload state is reached.
Commonly used overload trip classes include 5, 10, 20, and 30, each suited for specific applications. Class 5 is ideal for situations requiring rapid response, while Class 10 suits most artificially cooled motors like submersible pumps with low thermal capacities.
Class 20 is fitting for general-purpose applications, balancing protection with reduced maintenance needs. Class 30 is best for equipment with high inertial loads to avoid unnecessary tripping.
Motor Overload Protection Solutions from NOARK Electric
The reliability of motorized equipment hinges on robust protection from unpredicted shocks and overloads. NOARK Electric emphasizes the importance of choosing the correct thermal or electronic overload relay tailored to a device’s specific requirements.
Their Ex9R thermal overload relay and Ex9RE electronic overload relay offerings are crafted by their in-house engineers, who leverage deep industry knowledge to provide top-tier solutions across various market segments.
Organizations worldwide trust NOARK to guide them in selecting the most appropriate overload relays and other low-voltage electrical components to meet their unique needs.
Overload relays provide reliable motor overload protection by preventing damage caused by phase failure, high temperatures, or electrical overload.
They’re usually connected in series to the contactor (or switching device) to protect the motor from problems associated with the motor drawing excess current that could lead to overheating and damage to windings. When operations depend on the safe and efficient function of a motor, it’s essential to keep it protected from as many potential sources of damage as possible.
What are the Main Types of Overload Relays?
When comparing overload relays, it’s important to understand differences in design. Each type of overload relay bears a significant impact on how efficiently the overload relay functions, and under which use cases one is more appropriate. Generally, motor overload protection will depend on one of two types of overload relays:
- Bimetallic Overload Relay: A bimetallic or thermal overload relay cuts power when it detects that the motor has drawn excessive current for a long duration. They are the more cost-effective option, but they use a bimetallic strip and heating element and, as such, store more heat. This makes them less accurate, particularly at higher temperatures.
- Solid State or Electronic Overload Relay: Electronic overload relays are more accurate than thermal relays. This is partly because electronic overload relays don’t have a bimetallic strip. Instead, electronic overload relays rely exclusively on an electrical circuit to detect when the overload conditions are met, making them more precise.
Which Overload Trip Class Should They Consider for Application?
Proper motor overload protection requires carefully matching the motor to the right overload relay. Most overhead relays function on an inverse time curve, where the tripping time decreases as the current increases. This is denoted by the overload trip class, a number that designates the duration, in seconds, before the relay opens after reaching its overload state.
The most common overload trip classes are 5, 10, 20, and 30, which trip after the same number of seconds. Typically, each trip class is appropriate for the following applications:
- Class 5 is considered extremely fast and used when motor overload protection depends on quick reaction speeds.
- Class 10 overload relays have a more moderate effect, making them a good choice for most artificially cooled motors (e.g., submersible pump motors with low thermal capacities).
- Class 20 is usually suitable for general-purpose applications, such as consumer goods. The slower trip speed provides an adequate balance between protection and reduced need for servicing or troubleshooting.
- Class 30 relays are the best choice for devices with high inertial loads. This prevents nuisance tripping, where an overload relay trips in the absence of a detectable fault.
Reliable Motor Overload Protection from NOARK Electric
However valuable the motorized equipment is, that’s how important it is to protect it from unexpected shocks and other causes of overload. Selecting the right thermal or electronic overload relay for the device depends equally on quality and industry knowledge.
With the Ex9R (thermal overload relay) and Ex9RE (electronic overload relay) offerings, they support the clients in the different market segments. The in-house engineers develop the most effective overload relays on the market for a wide range of motor applications. With global reach, clients across numerous industries count on them to help them select the right overload relays and other low-voltage electrical components for their exact needs.
