Temperature fuse 5x20mm Temperature fuses are components designed to switch off a device by automatically opening the circuit if the permissible operating temperature of the device is exceeded. The nominal switch-off temperature can only be set by the manufacturer. To restore the circuit, the temperature fuse must be replaced as a whole. The temperature fuses have a rigid housing in a dust and dirt-proof design. They react to the ambient temperature and are conditionally sensitive to current at nominal load.