The Siemens 3RU2126-4BB0-ZW96 is a SIRIUS thermal overload relay, size S0, with a Class 10 trip characteristic. It's the part that sits between the contactor and the motor on a DIN-rail panel, watching current draw and tripping if the motor starts cooking. The note on this variant reads "Tripped" — a clear signal that the relay has done its job and the load needs a look before a reset.
What the Ratings Mean for Fit
The Class 10 trip class means this relay will open the circuit within 10 seconds at a 600% overload — fast enough to protect a standard motor winding from a locked-rotor event. The S0 frame size (45 mm wide, 85 mm deep) tells you it mates with the S0 contactor footprint; it mounts directly onto the contactor via the fastening method listed, no extra bracket needed. Rated insulation voltage of 690 V covers most 400 V and 480 V systems with headroom. The auxiliary switch is integrated into the housing, so you don't need a separate add-on block for a status signal back to the PLC. The screw-type terminals on the main circuit accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire — a Pozidriv PZ 2 screwdriver tip is what you want in the panel-build kit. Operating temperature range of -40 to +70 °C means it will survive a hot motor control center in summer and a cold start in an unheated pump house. Temperature compensation is active from -40 to +60 °C, so the trip curve stays accurate even when the panel is sweating or freezing.