What it is and what it does
The Siemens 3RU7146-4HB0 is a SIRIUS S3 thermal overload relay rated for 50 A operational current, designed to protect three-phase AC/DC motor circuits against overload and phase failure. The thermal bimetallic release follows a Class 10 trip characteristic, meaning it must trip within 10 seconds at 7.2× the set current — the standard for standard-start induction motors on conveyors, pumps, and fans where the start-up time is under 10 seconds.
Mounting and integration
Fastens directly onto a S3-size contactor (no DIN rail bracket needed), which saves panel width. The relay itself is 70 mm wide, 120 mm tall, and 140 mm deep — dimensions that matter when you're swapping into an existing panel layout. Mounting position allows ±135° rotation and ±45° tilt from vertical, giving flexibility in tight enclosures. Screw terminals on both main and auxiliary circuits: main terminals torque to 4–6 N·m, auxiliary to 0.8–1.2 N·m. Accepts 2× (0.5–1.5 mm²) or 2× (0.75–2.5 mm²) solid/stranded wire.
Environmental and electrical limits
Operates from -20 to +55 °C, with 0–90% relative humidity. Installation altitude max 2 000 m. Rated insulation voltage 1 000 V AC (pollution degree 3), surge voltage resistance 8 kV. Front face is IP20 (finger-safe), terminals are IP00 (no protection) — so the relay needs to be inside a panel or enclosure. Total typical power loss at rated current is 15.3 W, with 5.1 W per pole — factor that into your enclosure thermal budget.