What it is and what it does
The Siemens 3RT1023-1BF40 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads in industrial control panels. It carries a 110 V DC coil that draws 5.4 W during both closing and holding — the DC hold is the same as the pull-in power, so the coil driver sees a constant load once picked. The contactor is rated for AC-2 duty at 400 V at 4 kW and AC-4 at 400 V at 8.5 A, which covers reversing and inching applications where the load is switched under full motor current. For AC-12 resistive loads it handles 10 A maximum. Motor power ratings are 4.5 kW at 500 V and 5.5 kW at 690 V, making it suitable for 400 V class motors in the 4 kW range with headroom.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022. The 45 mm width and 85 mm height fit standard S0 panel layouts. Side-by-side mounting is permitted, which saves rail space in multi-contactor groups. Screw-type terminals on both main and auxiliary circuits accept 2x (0.5...1.5 mm²) solid or 2x (0.75...2.5 mm²) stranded for control wiring, and up to 2x 10 mm² on the main poles. AWG equivalents are 2x (16...12) solid and 2x (14...10) stranded for mains.
Protection and environment
IP20 on the front face protects against finger contact; the terminal area is IP00, so the contactor must be installed inside an enclosure. Operating temperature range is -25 to +60 °C, with pollution degree 3 rating for industrial atmospheres with conductive contamination. Type 1 coordination requires a 63 A gL/gG fuse; Type 2 coordination needs a 25 A gL/gG fuse. This lets the designer choose between simpler coordination (Type 1) or reduced downstream damage after a fault (Type 2).
Lifecycle and sourcing
RoHS compliance is confirmed with a substance prohibition date of 01.07.2006, covering the original EU RoHS directive.