What it is and where it sits
The 1SAZ721201R1055: Legacy mark on the device is ASEA BROWN BOVERI — same 1SAZ721201R10xx family that pairs with ABB contactors in motor-starter assemblies.
Where this class works in a panel
Solid state overload relays of this kind sit downstream of the contactor and upstream of the motor, set to trip on sustained overcurrent from a stalled-rotor or jammed-load condition rather than on a brief inrush — so the relay's current range and trip class, not just its presence in the starter string, decide which contactor frame it can ride on.