What it is and what it does
The Siemens SIRIUS 3RU2126-1HB0-ZX95 is a thermal overload relay in the S0 frame size, designed to protect motors against overcurrent and phase failure. It's a CLASS 10 device, meaning it will trip within 10 seconds at 7.2x the set current — essential for motors with short starting times, like pumps and compressors, where a slower trip would let the winding overheat before the relay acts. The overload release is thermal, bimetallic, with an integrated auxiliary switch that provides a "Tripped" message output. That integrated switch is what the "ZX95" suffix flags — a factory-fitted auxiliary contact for remote trip indication, not a separate add-on block.
Mounting and integration
Mounts directly onto a contactor via the "Contactor mounting" fastening method — no DIN rail required for the relay itself, though the contactor it sits on will typically snap onto a DIN rail. Mounting position is any, so vertical or horizontal panels are fine. Screw-type terminals on the main circuit accept 2x (0.5 to 1.5 mm²) solid or stranded, or 2x (0.75 to 2.5 mm²); the auxiliary terminals follow the same range. Use a Pozidriv PZ2 screwdriver with a 5 to 6 mm shaft diameter. Dimensions are 45 mm wide, 85 mm deep, and 85 mm high — the S0 frame footprint is compact enough for a 45 mm-wide DIN-rail slot when paired with the matching contactor. The main contact screws are M4.
Sourcing and lifecycle reality
Lifecycle stage is listed as "current" — meaning Siemens still produces this exact order code today, not a phased-out or NRND variant. The "ZX95" suffix is a factory-coded auxiliary contact configuration, so if your BOM calls for this exact code, you're getting the integrated trip-indication switch as a standard production item, not a custom or obsolete option. No successor is listed because none is needed. Sourcing posture: this is a standard catalog item within the SIRIUS family, quoted to order against an RFQ. For a BOM freeze or line-down replacement, the key fit check is the S0 frame size and the CLASS 10 trip curve — those are the specs that decide whether it mates with your existing contactor and protects your motor within the required start time.