Siemens 3RU1146-4FD0 — SIRIUS Thermal Overload Relay, CLASS 10, Size S3
It mounts directly onto a contactor (contactor mounting per), making it a compact, integrated solution for a motor starter in a control panel. The front face carries IP20 protection, meaning it is finger-safe when installed in an enclosure, and the unit is ATEX approved (DMT 98 ATEX G 001,) for use in potentially explosive atmospheres.
This is the standard for standard-duty motor starting — it lets the motor accelerate through inrush without nuisance tripping, but clears fast enough on a locked rotor. For a pump or fan on a normal start, CLASS 10 is the default; if you have a high-inertia load (centrifuge, long conveyor), you would step up to CLASS 20 or 30 — this part is not that. The auxiliary contact ratings are given for multiple control voltages: 1 A at 24 V, 3 A at 120 V, 2 A at 230 V, and 1 A at 400 V. These are the switching currents the built-in N/O and N/C aux contacts can handle. For a 24 VDC PLC input, the 1 A rating is generous; for a 120 VAC control circuit, the 3 A rating handles multiple contactor coils in parallel. The surge voltage resistance is 8 kV, which gives solid margin for industrial line transients. Power dissipation is 4.5 W per pole. In a dense panel with three relays, that is 13.5 W of heat to manage — not a showstopper, but worth noting if the enclosure is tightly packed and poorly ventilated.
Integration and Mounting — Panel Fit
Fastening method is contactor mounting, meaning it clips onto the front of a matching SIRIUS contactor (e.g., 3RT50 series). This saves DIN rail space and reduces wiring between the relay and contactor coil. Dimensions: 70 mm wide, 120 mm high, 140 mm deep. The depth of 140 mm is the protrusion from the contactor face — check your enclosure depth if you are retrofitting into an existing panel that was tight on clearance. Mounting position is flexible: the relay can be rotated ±135° on a vertical surface, or tilted ±45° front-to-back. This is useful for angled sub-panels or when the contactor is mounted on a swing frame. Side clearance of 6 mm is required; no clearance needed upwards, forwards, backwards, or downwards. Main circuit terminals are screw-type accepting 2x (10…50 mm²) stranded or 1x (10…70 mm²). Auxiliary and control circuit terminals are Cage Clamp for 2x (0.5…2.5 mm²) solid. The mixed terminal types mean you need both a screwdriver for the power side and a small cage-clamp tool for the control wiring — common on SIRIUS gear, but worth flagging to the panel builder.
For type of coordination 2 (short-circuit protection with minimal damage to the starter), a gG fuse of 80 A is required. For type 1 coordination (starter may be damaged but no hazard), a gG fuse of 160 A is specified. These are the fuse ratings for the main circuit; the relay itself must be set to the motor FLA. The part carries ATEX approval (DMT 98 ATEX G 001,) for gas atmospheres. Substance prohibitance date is listed as 07/01/2006, which aligns with RoHS compliance timing.