What it is and what it does
The Siemens 3RU2116-1KC0 is a SIRIUS thermal overload relay, Size S00, designed to protect motors against overload and phase failure. It uses a thermal bimetallic release that tracks the motor's heating curve, tripping the connected contactor when current exceeds the set threshold for too long. Rated for 690 V and Trip Class 10, meaning it will trip within 10 seconds at 7.2× the set current — standard for general-purpose induction motor starting where the inrush decays fast. This keeps nuisance trips off your line while still catching a locked rotor. Mounts directly onto a SIRIUS contactor (contactor mounting), saving DIN rail space and simplifying the power bus between the two devices. Any mounting position is permitted, so panel layout is flexible.
Key ratings and what they mean for fit
Motor power ratings: 5.5 kW at 400 V, 7.5 kW at 500 V, and 7.5 kW at 690 V — these are the AC-3e (squirrel-cage motor) values that govern real-world motor sizing. Also carries a 12.5 A rating at both 480 V and 600 V for North American installations. Switching capacity at various control voltages: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V, 0.75 A at 690 V. These are the auxiliary contact ratings — the relay's internal integrated auxiliary switch handles the contactor coil or PLC input, not the motor power. Temperature compensation is active from -40 to +60 °C, so the trip curve stays accurate across the panel's ambient range. The relay itself operates from -40 to +70 °C and can be stored or transported from -55 to +80 °C. Power dissipation per pole is 2.2 W — relevant for enclosure heat calculations when multiple relays are ganged in a small panel.
Wiring and integration
Main current circuit uses spring-loaded terminals, accepting 2x (0.5 to 2.5 mm²) solid or stranded wire. No screw torque to verify — just strip 8–10 mm and push in. The auxiliary switch is integrated, so no separate block to order. Dimensions: 45 mm wide, 87 mm high, 70 mm deep — fits the standard S00 footprint. The depth is the critical dimension when the relay is mounted on the contactor, as it projects forward from the contactor face. The note on this unit reads "for message 'Tripped'" — meaning the auxiliary contacts are configured to signal a tripped state back to the PLC or annunciator, not just drop out the contactor. Useful for remote fault indication.
Lifecycle and sourcing
Substance prohibitance date of 10/01/2009 aligns with RoHS compliance (RoHS took effect 2006, with some exemptions). The relay is part of the SIRIUS family, widely used in European and global panel designs. MTTF with high demand rate is 2,280 years — a reliability figure for safety-related applications, indicating very low random failure rate under continuous cycling.