What it is and what it does
The Siemens 3RU1116-1AC1 is a SIRIUS thermal overload relay — the device that sits between a contactor and a motor, protecting against overload by monitoring current and heating a bimetal strip. Its CLASS 10 trip class means it will open the circuit within 10 seconds at 7.2× the set current, which is the standard for standard induction motor starting (covers most pump, fan, and conveyor starts without nuisance tripping). Rated for AC-3 duty up to 690 V, this relay handles the switching of squirrel-cage motors during starting and running. The size S00 footprint (45 mm wide, 92 mm high, 78 mm deep) is the smallest in the SIRIUS modular system, designed for direct mounting to a matching contactor or as a stand-alone unit.
Key ratings and what they mean for fit
Trip class CLASS 10 is the deciding factor for motor protection: it coordinates with most IEC standard motors up to 10 seconds of locked-rotor time. If your motor has a longer acceleration curve (high-inertia loads like centrifuges), you would need CLASS 20 or 30 — but for general-purpose three-phase motors this is the correct match. The main circuit uses Cage Clamp terminals accepting 2x (0.5... 2.5 mm²) solid or 2x (0.5... 1.5 mm²) finely stranded with ferrule. That covers the typical control wiring range for motor circuits up to around 7 A (depending on the contactor partner). The auxiliary contact block is not included (0 auxiliary contacts as standard), so plan for a separate 3RU1900-.. series block if you need N/O or N/C signaling. Power dissipation is 5.7 W total at AC hot operating state (1.9 W per pole). In a densely packed panel, that heat adds up — the S00 frame is small, so ensure ventilation or spacing per the derating guidelines if ambient exceeds 40 °C. Surge voltage resistance is rated at 6 kV, which aligns with IEC 60947-1 overvoltage category III for industrial control panels. The IP20 front protection means it is touch-safe on the front face but not sealed against dust or moisture — install inside an enclosure rated for the environment.
Where it is used
This relay is deployed in motor control centers (MCCs), distribution boards, and standalone starter assemblies across manufacturing, water treatment, HVAC, and material handling. The ATEX certification (DMT 98 ATEX G 001) permits installation in potentially explosive gas atmospheres (Zone 1 or 2) when paired with an appropriate contactor and enclosure — a common requirement in chemical, oil and gas, and grain handling facilities. Mounting position is flexible: vertical surface with ±135° rotation and ±45° tilt front/back, which helps when fitting into tight or angled panel layouts. The stand-alone installation style means it can be snapped onto a DIN rail or screw-mounted directly, not only paired with a contactor.