The Siemens 3RU2116-0BJ0 is a SIRIUS thermal overload relay in size S00, Trip Class 10, designed to protect motors against overload and phase failure by monitoring current and tripping the contactor. The relay mounts directly to the contactor (fastening method: contactor mounting), keeping the panel layout tight and the power loop short. Main circuit connections use ring cable lugs (M3 screw size), so expect to crimp rings on your motor leads — no fork terminals here. Auxiliary switch is integrated, giving you a single changeover contact for the control circuit. The auxiliary contact ratings span the control voltages you'll actually find in a panel: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V. That 1 A at 400 V is your signal back to the PLC over a longer run without voltage drop issues.
Built for the environment it lives in
This relay shrugs off the vibration and dust you get in a mill or conveyor gallery. Temperature compensation is active from -40 to +60 °C, so the trip curve stays accurate even when the panel is sitting next to a hot motor or in a frozen yard. The screwdriver spec (Pozidriv PZ2, shaft diameter 5–6 mm) is what every panel wireman carries; no special tools needed.