The Siemens 3RU2126-4AC0-ZX95 is a SIRIUS thermal overload relay in size S0, designed for motor protection with Trip Class 10. It mounts directly to a contactor and accepts spring-loaded terminals for the main circuit, accepting 2x (0.5 to 2.5 mm²) solid or stranded wire. The relay provides thermal overload protection with temperature compensation from -40 to +60 °C, and carries a rated insulation voltage of 690 V for AC-3e duty.
What the ratings mean for fit
Trip Class 10 means the relay trips within 10 seconds at 7.2× the current setting — standard for protecting standard induction motors during start-up. The 690 V rated insulation voltage (AC-3e) covers 400 V and 480 V line-to-line systems common in European and North American panels. The auxiliary contact ratings span 24 V at 2 A up to 400 V at 1 A, so the N/O or N/C signal can switch a PLC input or a contactor coil directly at those voltages without an interposing relay. The S0 frame size and 45 mm width mean it fits standard SIRIUS contactor mounting rails. Mounting position is any, which simplifies panel layout when space is tight. The spring-loaded terminals (cage clamp) accept up to 2.5 mm² — no screw torque to verify, just strip to 8–10 mm and push in.