A11.0 | Schneider Electric Thermal Unit

Thermal units serve the purpose of safeguarding motors, controllers, and branch circuit conductors against excessive heating resulting from prolonged motor overcurrents, including locked rotor currents. The protection of the motor and other branch circuit components from higher currents, stemming from short circuits or grounds, is primarily facilitated by branch circuit fuses or circuit breakers. Class 20 thermal units are designed to react to overload current conditions in accordance with trip curves. These thermal units are engineered to trip in 20 seconds or less upon detecting overload conditions. 

Constructed as single-piece units, these thermal units feature a compact design. Within these thermal units, the motor current traverses a small heater winding. In the event of overload conditions, the generated heat leads to the melting of a special solder, which, in turn, permits a ratchet wheel to spin freely. This action results in the opening of the control circuit contacts and subsequently, the motor contacts, thus interrupting the circuit and mitigating the risk posed by overload currents.