What it is and what it does
The Siemens 3RT1023-1BP40 is a SIRIUS S0-frame power contactor for switching motor loads in control panels. It carries a 4 kW rating at 400 V in AC-2 duty (slip-ring motors, reversing) and 8.5 A in AC-4 (plugging, inching). The 24 VDC coil draws 5.4 W on pick-up and hold — no economizer needed, but verify free-wheel diode polarity on the DC side before energizing inductive loads downstream.
Mounting and integration
Snap-on mounting onto 35 mm DIN rail per EN 50022. The S0 frame footprint is 45 mm wide, 85 mm tall, 101 mm deep — fits standard panel layouts. Side-by-side mounting is permitted with 6 mm spacing to adjacent devices. Pollution degree 3 environment rated, so it handles conductive dust and humidity typical of industrial enclosures without conformal coating.
Termination and coordination
Screw-type terminals on the main circuit accept 2x (1–2.5 mm²) solid or 2x (2.5–6 mm²) stranded, up to 2x 10 mm² max. For type 2 coordination (no weld), use gL/gG fuses at 25 A; type 1 coordination allows 63 A fuses. The auxiliary contact block is rated for 10 A AC-12 (resistive) and switches down to 0.3 A at 220 V DC — useful for PLC-level signal isolation.