Contactor Overload Relays

Contactor overload relays are indispensable safety devices that protect electric motors from the damaging effects of overcurrents. Often referred to as thermal overload relays or simply overload relays, these devices safeguard against motor thermal overload.

At the heart of their operation is a bi-metallic strip, which bends when excessive current flows through the motor, triggering a mechanism within the thermal overload contactor. This action disconnects the motor from the power supply, providing vital thermal overload protection. Once the motor cools, the contactor with overload relay resets, allowing normal operation to resume.

By preventing costly motor damage and ensuring operational safety, these relays offer substantial value, and their overload relay price is a worthwhile investment for any industrial or commercial setting relying on electric motors.

What is Overload Protection?

Overload is where a motor draws a high current above its rated value for an extended amount of time. Overload causes overheating of the motor causing damage. To prevent this from happening, devices such as contactor relays are specifically designed for industrial control motor protection. They are used with contactors as part of a motor starter or in a control panel or centre.

What Are the Different Types of Contactor Overload Relays?

Motor protection devices can be classified into two main types which are thermal types and electronic types.

Thermal Overload Relays

Utilise a bi-metallic plate located near a heating element. When excessive current is passed through the heating element N/C (Normally Closed) contacts switch over and open contacts. This interrupts power from flowing to the contactor's control circuit. Thermal overloads usually offer an adjustable current range as well as a manual or automatic reset option.

Electronic Relays

Electronic overload relays don't have a bi-metallic mechanism. Instead, they work by using components such as temperature sensors to measure the load current. They are generally more accurate than thermal devices, and they usually have a wider current range. A selectable trip provides enhanced trip protection against single phasing against the motor.

Thermal Overload Relay vs Thermal Fuses

While both thermal overload relays and fuses protect motors from excessive current, they differ in their operation and applications.

• Thermal Overload Relays: Offer adjustable protection, tripping at a specific current level and automatically resetting once the motor cools down. Ideal for frequent starts and stops, as well as motors prone to temporary overloads.
• Thermal Fuses: Provide one-time protection, melting and permanently opening the circuit when a specific temperature is reached. Best suited for situations where a single overload could cause catastrophic damage.

Standards and Certifications

Look for contactor overload relays that adhere to stringent industry standards and certifications to ensure safety and reliability. These guarantee that the thermal overload relays meet specific performance criteria and provide adequate overload protection for motors.

• IEC 60947-4-1: International Electrotechnical Commission standard for low-voltage switchgear and control gear assemblies, including thermal overload relays.
• UL 508: Underwriters Laboratories standard for industrial control equipment, covering motor overload relays and other protective devices.

Industry Applications

Contactor overload relays are vital for safeguarding electric motors across diverse industries, ensuring smooth operations and preventing costly downtime due to motor thermal overload.

Specific Applications:

• Manufacturing: Contactor overload relays play a critical role in protecting motors driving production machinery, such as conveyor belts, pumps, and fans. By preventing motor burnout from overcurrents, they ensure smooth operation and uninterrupted production processes.
• HVAC Systems: Thermal overload relays safeguard motors in heating, ventilation, and air conditioning systems. They protect blower motors, compressor motors, and other critical components, preventing equipment failure and ensuring comfortable indoor air quality.
• Construction: In construction applications, contactor overload relays shield motors in cranes, hoists, and other equipment from overloads, promoting safety and preventing damage during construction projects.
• Agriculture: Motor overload relays are essential in agricultural equipment like irrigation pumps, grain elevators, and livestock feeding systems, ensuring reliable operation and protecting valuable machinery.
• Transportation: These overload relays find applications in various transportation systems, including escalators, elevators, and conveyor systems, ensuring passenger safety and preventing equipment breakdowns.

Your Trusted Thermal Overload Relay Supplier & Manufacturer

RS is your trusted source for high-quality contactor overload relays and thermal overload relays from leading brands like Siemens, Schneider Electric, ABB, and more. As a reliable overload relay supplier and manufacturer, we offer a wide selection to meet your specific needs at a competitive price.

To buy our contactor or thermal overload relays, simply visit our product page and filter according to your specific requirements. We make it easy to find the perfect match for your system. In addition, we also offer a range of industrial circuit breakers or vfd drives to protect your electrical circuits and motors. Need more information on delivery? Check out our Delivery page for details on services and fees.