What it is and what it does
The Siemens 3RU2126-1JB0-ZX95 is a SIRIUS thermal overload relay — S0 frame size, Class 10 trip curve, rated 690 V. It's the part that sits between a contactor and the motor, watching current and tripping on overload before the winding insulation gives up. The thermal bimetallic release means it tracks the motor's heating curve naturally, no electronics to fail in a vibration-heavy panel. It's built for contactor mounting (bolts straight onto the contactor's output side) with screw-type terminals for the main circuit. The auxiliary switch is integrated — no add-on block needed — and carries the 'Tripped' signal back to the PLC or indicator lamp.
What the ratings mean on site
Class 10 trip class means it'll open within 10 seconds at 7.2× the set current — fast enough to protect a standard squirrel-cage motor starting a pump or conveyor, but not so fast it nuisance-trips on a normal start. The S0 frame is the mid-size in the SIRIUS family; it handles motor power up to 7.5 kW at 690 V. The auxiliary contact ratings cover most control voltages you'll find in a panel: 2 A at 24 V and 230 V, 3 A at 120 V, 1 A at 400 V. That's enough to drive a PLC input or a small relay directly without an interposer. Temperature compensation is active from -40 to +60 °C, so the trip point doesn't drift when the panel heats up in summer or the line runs near a furnace. Operating range is -40 to +70 °C; storage and transport handle -55 to +80 °C.
Mounting and wiring
Mounts directly to the contactor — no DIN rail bracket needed, no extra hardware. Accepts 2× (0.5 to 1.5 mm²) or 2× (0.75 to 2.5 mm²) solid or stranded wire per terminal. Screw terminals take a Pozidriv PZ2 bit, shaft diameter 5 to 6 mm. Main circuit connections use M4 screws. Dimensions are 45 mm wide, 85 mm deep, 85 mm tall — fits the standard S0 footprint. Mounting position is any, so you can lay it sideways in a shallow enclosure if needed.
Lifecycle and sourcing
This is a current-production part in the SIRIUS portfolio. No end-of-life notice, no last-time-buy deadline — it's the standard thermal overload relay for S0 contactors and will be for the foreseeable future. Quoted to order against an RFQ for BOM-line commitments.