PTC thermistor relay is a type of relay that uses a positive temperature coefficient (PTC) thermistor as its sensing element. PTC thermistors are resistive devices that have a positive temperature coefficient, meaning that their resistance increases as their temperature rises.
In a PTC thermistor relay, the PTC thermistor is connected in series with the load (such as a motor or heater) and the power source. When the load is switched on, the PTC thermistor heats up along with the load, causing its resistance to increase. As the resistance of the PTC thermistor increases, it limits the current flow through the load and prevents it from drawing too much current.
PTC thermistor relays are commonly used for overload protection in motors and heaters, as they provide a simple and reliable way to protect the load from excessive current. They are also used in automotive applications for temperature sensing and control.