What it is and what it does
The Siemens 3RU2116-1FB1 is a SIRIUS thermal overload relay — size S00, Class 10 trip curve, with a thermal bimetallic release for motor protection. Rated for main circuits up to 690 V, it's the go-to for protecting S00-frame contactors in motor starter assemblies. The integrated auxiliary switch signals a tripped state, and the standalone fastening means it mounts independently, not ganged to a contactor base.
Key ratings and what they mean for fit
Class 10 trip class means it will trip within 10 seconds at 7.2× the current setting — fast enough to protect standard induction motors during a locked-rotor event, but not so fast it nuisance-trips on normal start-up. The S00 frame size keeps the footprint compact: 45 mm wide, 89 mm tall, 80 mm deep, so it fits in tight panel layouts. Power dissipation is 2.2 W per pole, which adds up to 6.6 W on a three-phase motor — not negligible in a sealed enclosure; plan for some airflow if you're stacking multiple starters. The auxiliary contact ratings cover a wide control voltage range: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, and 1 A at 400 V — so it can drive a PLC input or a contactor coil directly across common control voltages without an interposing relay.
Where it's used
This relay is the overload protection half of a motor starter pair — mate it with a SIRIUS S00 contactor (like the 3RT1015) and you've got a coordinated motor start/stop and protection block for conveyors, pumps, fans, and compressors. The temperature compensation from -40 to +60 °C means it holds its trip curve accuracy in unconditioned enclosures or outdoor cabinets.