What this heater pack does
The ABB 1SAZ721201R1028 is a thermal overload heater pack listed under the Contactors and Starters family, sized to a 1.3-1.7 A setting range so it drops onto a small-frame contactor to protect fractional-horsepower motors in that band. It is a consumable heating element that sits inside the overload relay base and trips the relay once sustained current exceeds the dialed setpoint.