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Thermal Overload Relay

As an overload protection element for motors, thermal relays are widely used in production due to their small size, simple structure, and low cost.


Theory:Thermal Relay
Usage:General Purpose
Protect Feature:Sealed
Contact Load:High Power
Type:General Purpose Power Relays
Condition:100% Original
Application:Electrical Appliance
Color:Gray White
Contact material:AgCdO


The working principle of the thermal relay is that the current flowing into the heating element generates heat, causing the bimetallic plates with different expansion coefficients to deform. When the deformation reaches a certain distance, the connecting rod is pushed to move, the control circuit is disconnected, and the contactor When the power is lost, the main circuit is disconnected to realize the overload protection of the motor.


1, When the thermal overload relay tripped, the trip indicator will go up 2-3mm; when the thermal overload relay on the mode of manual reset, you can put on the reset button to reset.

2, Automatic reset: put on the reset button and turn 90 anticlockwise

3, Main circuit terminal and control circuit terminal is clearly distinguished to avoid wrong wiring by manual.

Function and role

It is mainly used for overload protection of asynchronous motors. His working principle is that after the overload current passes through the thermal element, the bimetallic sheet is heated and bent to push the action mechanism to drive the contact action, thereby disconnecting the motor control circuit to realize the motor power off , Play the role of overload protection. In view of the fact that during the bending process of the bimetal, the heat transfer takes a long time. Therefore, the thermal relay cannot be used for short-circuit protection, but can only be used as overload protection for the overload protection thermal relay.


It consists of heating elements, bimetallic strips, contacts and a set of transmission and adjustment mechanisms. The heating element is a piece of resistance wire with little resistance, which is connected in series in the main circuit of the protected motor. The bimetallic sheet is formed by rolling two metal sheets with different thermal expansion coefficients.


It is mainly used in the electric system with AC 50HZ/60HZ, it is used to protect AC 3phase asynchronous motor against overload and open-phase. This products can be properly combinaed with contactors and installed in an encloser as motor starter to protect the motor from overload and open phase.





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