The ZH037 K series is a tripping device intended to provide a fail-safe thermal output protection to prevent overheating specifically in electric air heaters used in rail vehicles and other heating systems. The ZH037 K series is an ideal device for fire safety and operate without the aid of heater control purposes. It has to be coiled unto the heater load circuit for it to release energy. The device must also be fitted with a fusible link which are available with certain number of temperatures for the user to acquire the single fusible link to meet the exact requirements of the application. This is also one of the reasons why fusible links are not included unto any deliveries of the product or in any over-temperature protection and tripping device.