Motor Thermal Overload Switch

For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor.

Motor thermal overload switch.

External motor overload switches ol switches do not include thermal protection there are external overload switches that can be wired into a motor circuit. A single use device that cannot be reset and must be replaced when it fails or is triggered a thermal fuse is used when the overheating is a result of a rare occurrence such as failure requiring. In that way all three phases are in contact with a thermal switch. As the rotating magnetic current intersects each bar conductor of the rotor there will be a rotating current of induction flowing through the bar conductor.

In single phase motors one single thermal switch is used. Due to such symmetrical distribution when three phase power supply. It is placed in the motor circuit in such a way that the current to the motor flows through its poles. A thermal fuse is a cutoff which uses a one time fusible link unlike a thermal switch which may automatically reset itself when the temperature drops the thermal fuse is more like an electrical fuse.

Diyhz thermal circuit breaker 30a 125 250v ac 32v dc push button reset thermal overload circuit breaker with quick connect terminals waterproof button cover 98 series 4 6 out of 5 stars 20 9 99 9. There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator. They are suitable for use with small machine tools pumps fans and conveyors. Square d type k manual motor switches provide manual on off control of single or three phase ac motors where overload protection is not required or is provided separately.

A thermal overload relay works in the principle of electro thermal properties in a bimetallic strip. At start up the rotor is stationary and the stator field rotates at synchronous speed the relative speed between the rotating field and the rotor is maximum. In three phase motors 2 thermal switches connected in series are placed between the phases of the motor.