What it is and what it does
The Siemens SIRIUS 3RU7146-4JB0 is a Size S3 thermal overload relay for 3-pole motor circuits, rated at 63 A operational current and 1000 V operating voltage (AC/DC). Its CLASS 10 trip characteristic means it will trip within 10 seconds at 7.2× the current setting — the standard for standard-start induction motors where the start time is under 10 seconds. The relay mounts directly onto a SIRIUS S3 contactor (contactor mounting) and is wired via screw-type terminals on both the main and auxiliary circuits.
What the ratings mean for fit
The 63 A rated operational current (AC-1/AC-3) determines the maximum motor FLA you can protect — size the relay so the motor's full-load amps fall within the adjustable range of the relay's thermal element. Front face is IP20 (finger-safe), but the terminal area is IP00 — live parts are exposed below the terminals, so the panel must maintain a minimum 6 mm spacing to grounded parts at the side. Terminals accept 2× (0.5 to 1.5 mm²) solid/stranded or 2× (0.75 to 2.5 mm²) finely stranded with ferrule; torque the main circuit screws to 4–6 N·m and auxiliary screws to 0.8–1.2 N·m. Mounting position is flexible — vertical surface with ±135° rotation and ±45° tilt — but the ambient operating range is -20 to +55 °C; derate above 40 °C if the load is continuous.
Lifecycle and sourcing
It is a standard catalog item from the Siemens SIRIUS line — order to specification, no last-time-buy constraints.