The 8329-028 Thermoswitch is a tubular devices featuring an outer shell made of high-expanding metal and internal struts made of low-expanding metal, with a pair of electrical contacts between them. The unit prevents possible damage from accidental
power overloading from the transmitter or equipment malfunction. The thermoswitch is normally closed and opens at a maximum safe temperature of +200°C (+392°F). Since the thermoswitch is connected in series with the transmitter interlock, it cuts off the transmitter power if the coolant temperature exceeds this value.