What it is and where it lands
The Siemens 3RT1023-1BA40 is a SIRIUS power contactor in the S0 frame size, designed for switching motor loads and resistive circuits in control panels. It snaps onto a 35 mm DIN rail per DIN EN 50022 and takes screw-type terminations on both main and auxiliary circuits. The 12 VDC coil draws 5.4 W on pickup and hold — same figure, so no economizer circuit inside; the coil stays at full power as long as it's energized.
What the ratings mean for fit
Rated operational current varies by voltage and duty. At 24 V it switches 10 A; at 230 V it handles 6 A; at 400 V it's rated 3 A. For motor loads under AC-2 duty (slip-ring motors, starting/stopping under load) at 400 V it's good for 4 kW. Under AC-4 (plugging, inching, reversing) at 400 V it carries 8.5 A — that's the tougher duty cycle, so if your application does frequent reversals, size on the AC-4 number, not the AC-1 or AC-3 line. The 690 V rating is 5.5 kW, which tells you this contactor is built for 400 V class panels but can handle higher-voltage motors at reduced current. Mechanical life is 10 million operations typical — that's the contactor body itself, not the contacts under load. Electrical life will be shorter and depends on switching current and duty. Ambient temperature range is -25 to +60 °C, which covers most indoor panel environments but not direct heat sources near ovens or furnaces. Pollution degree 3 means it's rated for industrial environments with conductive or dry non-conductive pollution — standard for an IP20-front device inside a closed panel. Fuse coordination: with Type 2 coordination (no damage to the contactor under short circuit) use a 25 A gL/gG fuse. With Type 1 coordination (contactor may need replacement after a fault) use a 63 A gL/gG fuse. The IP20 rating on the front means finger-safe; the terminal area is IP00 — bare live parts when the panel door is open, so standard lockout/tagout applies.
Mounting and wiring
Width is 45 mm, height 85 mm, depth 101 mm — fits a standard S0 footprint. Side-by-side mounting is allowed with no derating gap, so you can pack multiple contactors on the same DIN rail. Main circuit terminals accept 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or max 2x (0.75 to 4 mm²) solid or stranded. Auxiliary terminals take 2x (1 to 2.5 mm²) or max 2x 10 mm². AWG equivalents are listed for both main and auxiliary circuits. The screw terminals are the same type throughout — no mix of spring-cage and screw on this variant.