280155 - Miller 280155 Thermal Protection Switch, NC 180F/155F

Technical Overview of the Miller 280155 Thermostat

The Miller 280155 is a precision-engineered thermal protection device designed specifically for Miller welding power sources. Functioning as a Normally Closed (NC) thermostat, this component plays a critical role in the safety interlock circuitry of welding equipment. Under normal operating conditions, the switch remains closed, allowing control current to flow and the machine to operate. However, should the internal temperature of the monitored component—typically a rectifier, transformer, or heat sink—rise to the critical threshold of 180°F (approximately 82°C), the bimetallic element within the switch actuates, opening the circuit.

This interruption of the circuit typically triggers the machine's thermal protection mode, stopping the welding output to prevent catastrophic damage to sensitive internal electronics. The device is designed with a specific hysteresis loop; once the component cools down to a safe operating temperature of 155°F (approximately 68°C), the switch automatically resets to its closed position, allowing the machine to resume operation. This automatic reset feature minimizes downtime while ensuring the equipment is never pushed beyond its thermal limits.

Physically, the 280155 features a robust flange mount design, allowing it to be securely bolted directly to the surface being monitored for accurate thermal transfer. Electrical connections are made via standard Faston (spade) terminals, facilitating quick and reliable replacement without the need for soldering. As an OEM part, it meets the exact specifications required for Miller equipment, ensuring proper fitment and reliable actuation temperatures that generic substitutes may not provide.