The Siemens 3RB3143-4XX1 is a SIRIUS solid-state overload relay in Size S3, designed to protect motors against overload and phase failure. It carries a rated thermal current of 115 A at both 480 V and 600 V, with a maximum operating voltage of 1 000 V. The trip class is field-adjustable among CLASS 5E, 10E, 20E, and 30E, letting you match the relay to the motor's starting characteristics — useful when the same panel builds see different load profiles.
Mounts in any position via stand-alone installation — no DIN-rail adapter required, though the 70 mm width and 106 mm height fit standard backpanel layouts. Depth is 124 mm, so account for that when spacing the enclosure door or adjacent components. The main current circuit uses straight-through transformers, meaning the motor leads pass directly through the relay body without looping. Screw terminals accept 2x (0.25... 1.5 mm²) solid or stranded wire; use a Pozidriv PZ 2 tip with a 5 to 6 mm shaft diameter.
The auxiliary switch is integrated into the relay body, with contact ratings spanning 24 V at 2 A, 120 V at 4 A, and 230 V at 3 A — enough to drive a PLC input or a contactor coil directly. The relay also provides a dedicated "tripped" message output (the Note on the order code references this), so the control system sees a distinct signal when the relay has operated, not just a generic fault.
The overload relay's trip threshold is set by the motor full-load current: the minimum trip occurs when IMotor is greater than the lower current setting value, and the maximum trip occurs when IMotor is less than the upper current setting value multiplied by 3.5. This gives a wide adjustment band for matching the relay to the motor nameplate. The S3 frame size covers the 115 A thermal current class, suitable for medium-horsepower motors in the 30–75 kW range depending on voltage and duty cycle.