A thermal Overload relay is a specialized overload protection component for motors, typically used in conjunction with an AC contactor. It operates on the principle of bimetallic strip thermal expansion to detect overload without electrical contacts, automatically breaking the control circuit when the motor experiences prolonged overload, locked rotor conditions, or abnormal temperature rise, thereby preventing winding burnout due to overheating. It serves as an essential safety component in motor control systems.

product highlights:

Bimetallic precision protection: Utilizes the thermal effect principle of bimetallic strips for overload detection, with a tripping accuracy of ±5% and a set current range of 0.1 A to 500 A covering all scenarios.

Phase failure protection against burnout: An optional phase failure protection function that monitors real-time three-phase current balance, eliminating the risk of motor burnout caused by single-phase operation.

Reliable temperature compensation: Built-in environmental temperature compensation mechanism (-20°C to +55°C) ensures consistent protection performance across various ambient temperatures.

Easy installation and reset: Supports direct plug-in or standalone installation with contactors, offering manual or automatic reset options. Equipped with test and stop buttons for easy maintenance.

The core working principle of the product relies on the thermal effect of bimetallic strips: two metal strips with different coefficients of thermal expansion are tightly bonded together. When motor overload causes an increase in circuit current and temperature, the bimetallic strips bend under heat, driving the mechanical transmission mechanism to open the contacts and cut off power supply to the contactor coil, thereby providing motor shutdown protection.
This principle features strong resistance to electromagnetic interference, stable operation, and low failure rate, making it suitable for long-term operation in complex industrial electromagnetic environments. The equipment supports switching between manual and automatic reset modes, allowing flexible selection based on field maintenance practices and unattended operation requirements.
To address the common phase loss fault in three-phase asynchronous motors, most models are equipped with optional phase-loss protection functionality that continuously monitors the three-phase current balance. Upon detection of a single-phase power outage or current imbalance, the system immediately activates protective measures, effectively preventing motor burnout caused by phase loss operation. The product housing is constructed from flame-retardant insulating material for robust durability and features standard rail mounting, allowing direct parallel installation alongside AC contactors within the cabinet with streamlined wiring and minimal space occupation.

application scenarios:

These devices are widely used in various types of MCC cabinets and motor control cabinets to protect conventional industrial motors such as fans, water pumps, conveyor belts, and mixers; in mechanical processing and automotive manufacturing lines to safeguard motors for machine tools, welding equipment, and conveying robots; in heavy industry sectors like power generation, metallurgy, and chemical processing to protect high-load motors including large fans, crushers, and compressors; as well as in small and medium-sized water pumps and fan motors within building HVAC and water supply/drainage systems.