Thermal Overload Relay for Contactor-Mounted Motor Protection
The Siemens 3RU1146-4LB0-ZX95 is a SIRIUS-brand thermal overload relay in Size S3, designed for contactor mounting to protect three-phase motors against overload and phase failure.
ATEX and Environmental Ratings
The front face is IP20, meaning finger-safe once installed in a panel. Shock resistance is 8g for 10 ms, adequate for most industrial machinery but not heavy-crane applications.
Mounts directly onto the matching SIRIUS contactor via the contactor-mounting fastening method — no separate base required. The mounting position allows rotation ±135° on a vertical surface and tilting ±45° front-to-back, giving flexibility in tight panels. Main circuit terminals accept screw-type connections: stranded 10–70 mm² (2x 10–50 mm²), or AWG 2x (10–1/0) and 1x (10–2/0). Auxiliary and control circuit terminals accept solid 2x (0.5–1.5 mm²) or 2x (0.75–2.5 mm²), and AWG 2x (20–16) or 2x (18–14). Dimensions: 70 mm wide, 120 mm high, 140 mm deep.
Auxiliary Contact Ratings and Coordination
The built-in auxiliary contacts (typically one N/C + one N/O for the trip/alarm) are rated: 1 A at 24 V, 3 A at 120 V, 2 A at 230 V, 1 A at 400 V, and 0.22 A at 110/125 V, 0.11 A at 220 V. For short-circuit coordination, with Type of Assignment 2 the required upstream fuse is gG 160 A; with Type of Coordination 1 it is gG 250 A. Per-pole power dissipation is 7 W — factor that into panel thermal calculations if the relay is enclosed without ventilation.
For a BOM-frozen design, this part is a qualified, stable choice. No official successor has been issued, so this remains the direct drop-in for any panel originally specified with the 3RU1146-4LB0-ZX95.