NEMA combination starter, Type S, 30A fusible disconnect, Size 0, 18A, 3HP at 240VAC, 3 phase, 3 pole, 120VAC coil, NEMA 1

Thermal units are intended to protect motors, controllers, and branch-circuit conductors against excessive heating due to prolonged motor over-currents up to and including locked rotor currents. Protection of the motor and the other branch circuit components from higher currents, due to short circuits or grounds, is a function of the branch circuit fuses or circuit breakers. Class 20 thermal units respond to overload current conditions according to trip curves. Combination starter has a 30 Amp Class H fuse clip. These thermal units have a one piece construction. The motor current passes through a small heater winding within these thermal units. Under overload conditions, the heat causes a special solder to melt allowing a ratchet wheel to spin free thus opening the control circuit contacts and opening the motor contacts.