What the part is
The ABB 1SAZ721201R1049 is a thermal overload heater element in the company's AF thermal overload family — a snap-on resistive element that defines the motor full-load-amp trip curve when seated in the matching thermal overload relay base. It sits in the starters and contactor-protection class, one tier under the circuit-protection umbrella, and its job is purely to set the current band for the overload relay it pairs with; the relay body, not the heater, carries the trip mechanism and auxiliary contacts.