Main parts

1) Insulating paper  2) Conductive housing  3) bimetal disc 

4) movable contact  5) stationary silver contact  6) base  7) iron nails

Construction

The stationary silver contact is welded on the base, the movable 

contact is welded to one end of the bimetal disc, the other end is 

welded to the housing by iron nails. The movable contact is in close 

contact with the stationary silver contact under the pre-pressure of

the bimetal disc, the base and the housing are isolated by insulating

paper. The current first passes through the movable contacts 

connected to the housing and bimetal disc, and then through the 

stationary silver contacts on the base to form a loop.

Function

When the circuit works normally,  the contact is in a closed state. 

When the rated operating temperature is reached, the bimetal disc 

is deformed by heat and snap rapidly, cut off the circuit. After that, 

the device begins to cool down. When it reaches the defined reset 

temperature, the bimetal disc and the spring disc snaps back into 

its start position, the contacts will close again, and the device starts 

working again.