The Siemens 3RU1146-4HB0 is a SIRIUS thermal overload relay — size S3, CLASS 10 trip curve, designed to protect motors against overload and phase failure by monitoring current and heating a bimetal strip that trips the contactor coil. It mounts directly onto a contactor (fastening method: contactor mounting), saving DIN-rail space and keeping the power wiring short — common in motor control centers and panel builds where every millimeter of width counts.
Trip class and coordination
CLASS 10 means the relay must trip within 10 seconds at 7.2× the current setting — standard for standard-duty induction motors (pumps, fans, compressors) that don't need a slower CLASS 20 or 30 for high-inertia starts. Short-circuit coordination is specified: with type of assignment 2, use a gG fuse rated 125 A; with type of coordination 1, use a gG fuse rated 160 A — this tells the panel builder which upstream fuse to select so the relay survives a fault without damage (coordination 2) or with acceptable damage (coordination 1).
Main circuit terminals are screw-type, accepting solid conductors from 10 to 50 mm² (2×) or stranded up to 70 mm² — sized for motor feeders up to roughly 55 kW at 400 V. Auxiliary and control circuit terminals are also screw-type, accepting solid wire 2× (0.5 to 1.5 mm²) or 2× (0.75 to 2.5 mm²), and AWG equivalents 2× (20–16) or 2× (18–14).
Relative humidity during operation can reach 100 % — suitable for condensing environments inside a sealed panel. ATEX certification (DMT 98 ATEX G 001) means the relay is approved for use in potentially explosive gas atmospheres when paired with an appropriate contactor and upstream protection.