It is placed in the motor circuit in such a way that the current to the motor flows through its poles.
Motor thermal overload switch.
Due to such symmetrical distribution when three phase power supply.
In single phase motors one single thermal switch is used.
That switch would monitor current draw amps and properly sized for the motor s specifications it could turn off the motor if the current draw is excessive as can happen with a bad.
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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.
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 that way all three phases are in contact with a thermal switch.
They are suitable for use with small machine tools pumps fans and conveyors.
There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator.
Thermal switches can be retrofitted on the coil end but the result is an increased reaction time.
For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor.
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.
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.
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