What it is
The ABB 1SAZ331201R1004 is a thermal overload heater pack from the thermal-overload-heaters-for-starters class, designed to clip onto a matching ABB contactor and provide the motor-circuit overload element that the contactor alone does not carry.
Where the class sits in the panel
Thermal overload heater packs of this class are the replaceable heat elements that complete a motor-starter assembly: the contactor handles switching, and the heater delivers the inverse-time overload characteristic sized to a specific motor full-load current range. In practice the heater is the component a panel builder reaches for when a motor is being retrofitted, when an existing starter is being re-rated, or when a service truck carries spares for a line that has to be back up before the next shift.
Sourcing and BOM fit
As an ABB catalog entry the 1SAZ331201R1004 is specified into the BOM by part number rather than by electrical parameter, so the safest path is to quote against the exact code on an RFQ and confirm heater setting range against the motor nameplate before release.