The Siemens 3RU7146-4LB0 is a SIRIUS S3 thermal overload relay, rated for 90 A operational current in the main circuit with a Trip Class 10 characteristic. It mounts directly onto a matching S3 contactor — no separate base or DIN-rail adapter needed, which keeps the panel footprint tight and the wiring loom short.
The 90 A rated current sets the motor FLA ceiling this relay can protect. If your motor has a longer acceleration ramp (high-inertia loads like centrifuges), you'd want a Class 20 or 30 relay instead; this one would nuisance-trip. The IP20 rating on the front means the operator interface is finger-safe; the IP00 terminal area expects the panel builder to provide the enclosure protection. Screw-type terminals on both main and auxiliary circuits accept 2x (0.5…1.5 mm²) solid or stranded, or 2x (0.75…2.5 mm²) — torque the main contacts to 4–6 N·m, aux contacts to 0.8–1.2 N·m.
Fastens directly to a SIRIUS S3 contactor — no DIN rail required, though the relay itself can be mounted on a vertical surface with ±135° rotation or ±45° tilt front-to-back. Side spacing to grounded parts: 6 mm minimum. Operating temperature range –20 to +55 °C; storage/transport –25 to +70 °C. Installation altitude limited to 2000 m. Dimensions: 120 mm high × 70 mm wide × 140 mm deep. The depth is the dimension that extends behind the panel face when contactor-mounted — check your enclosure depth if retrofitting into a shallow cabinet. Total typical power loss at rated current: 21 W.