I have a shredder that cuts out when it overheats too. It's a PTC thermistor controlling a relay, the thermistor is glued to the motor housing and the relay coi

I have a shredder that cuts out when it overheats too. It's a PTC thermistor controlling a relay, the thermistor is glued to the motor housing and the relay coil contact is wired through it. When it heats up too much, the resistance increases to the point that the relay is no longer receiving enough current, and it de-energizes and opens its contacts, breaking the motor's power supply.