What it is and what it does
The Siemens 3RU2126-1KB0-ZX95 is a SIRIUS thermal overload relay in the S0 frame size, designed to protect motors against overload and phase failure by monitoring the motor current and tripping the associated contactor when the thermal model reaches the threshold. It is a CLASS 10 trip class device, meaning it will trip within 10 seconds at 7.2× the set current — a standard protection class for most general-purpose induction motors where a fast trip is needed to prevent winding damage during a stall or jam. The relay mounts directly onto a contactor (fastening method: contactor mounting), so it shares the same DIN-rail or screw-panel footprint as the contactor it pairs with, keeping the panel layout compact.
Auxiliary contact ratings — what they mean for your control circuit
The integrated auxiliary switch provides a signal output — a 'Tripped' message — that can be wired into the PLC or annunciator. Its contact ratings vary by voltage: 2 A at 24 V, 3 A at 120 V, 2 A at 230 V, and 1 A at 400 V. These are the maximum continuous currents the auxiliary contacts can switch at those voltages; for DC applications the ratings drop significantly (0.3 A at 60 V, 0.22 A at 110 V, 0.11 A at 220 V). The auxiliary switch is designed as an integrated part of the relay — no separate add-on module needed — which simplifies ordering and panel wiring.
Environmental and mounting details
The relay is temperature-compensated over -40 to +60 °C, so the trip curve stays accurate across the typical panel ambient range. It can be mounted in any position, which gives flexibility in dense enclosures. Dimensions are 85 mm depth, 45 mm width, 85 mm height — the S0 footprint common to this Siemens series. Screw terminals accept 2× (0.5 to 1.5 mm²) or 2× (0.75 to 2.5 mm²) solid or stranded wire, with a Pozidriv PZ2 screwdriver tip. Storage and transport temperature range is -55 to +80 °C; operating range is -40 to +70 °C. The substance prohibitance date of 10/01/2009 indicates RoHS compliance per the EU directive.