You may be confusing Contactor Heaters which are often called Fuses but both are esssentially misnomers.
Contactor Heaters actually do not heat anything, they mimic the heating profile of electric motors. They are often called shunts but they are really set up in series so that all the power going to the motor runs through them. This makes them heat up, and the sizing of these is suppose to match the "heating up" that the motor is experiencing. At a certain point they warp like a thermostat and push open the main contactor.
Then they are suppose to cool the same way as the motor does, and at the point where they are cool they can be manually reset (some are auto reset).
So these are very mis-named as Motor Shunts, Motor Shunt Breakers, Contactor Heaters etc.... They are simply a thermal overload device that is not part of the motor itself.
Contactor Heaters actually do not heat anything, they mimic the heating profile of electric motors. They are often called shunts but they are really set up in series so that all the power going to the motor runs through them. This makes them heat up, and the sizing of these is suppose to match the "heating up" that the motor is experiencing. At a certain point they warp like a thermostat and push open the main contactor.
Then they are suppose to cool the same way as the motor does, and at the point where they are cool they can be manually reset (some are auto reset).
So these are very mis-named as Motor Shunts, Motor Shunt Breakers, Contactor Heaters etc.... They are simply a thermal overload device that is not part of the motor itself.