What it is and what it does
The Siemens SIRIUS 3RT1015-2BP42 is a size S00 power contactor, the smallest frame in the SIRIUS family, built for switching loads in control panels. It's rated for 10 A in AC-12 duty, which is the resistive-load category — think heaters, incandescent lamps, or transformer primaries where inrush is modest. The 230 V AC coil is a standard industrial control voltage across Europe and much of Asia. The AC-12 rating is the headline number that governs the fit: 10 A at the rated insulation voltage. That's not a motor-switching figure — for motor loads you'd look at the AC-3 or AC-4 ratings, which are lower for this frame size. At 230 V the contactor is rated for 6 A (AC-1), and at 400 V for 3 A (AC-1). The AC-4 rating at 400 V is 6.5 A, which covers reversing or inching duty on smaller motors.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022 — standard for any European-style panel. The 45 mm width (one HP, or horizontal pitch) means it occupies a single 9 mm module space on the rail. Depth is 73 mm, height 60 mm, so it clears most shallow enclosures. Side-by-side mounting is permitted, which is useful when packing multiple contactors into a tight gland plate layout. Main circuit connections are spring-loaded terminals, accepting 2x (0.25 to 2.5 mm²) solid or stranded wire, or 2x (24 to 14 AWG). Spring-cage terminations are faster to wire than screw clamps and hold well under vibration — worth noting if the panel sees transport or machine-mounted duty. The IP20 rating on the front and at the terminals means it's protected against finger contact but not against moisture; keep it inside a sealed enclosure. Degree of pollution 3 means the contactor is rated for conductive pollution environments — typical of industrial control panels where dust, moisture, or condensation may be present. It's not a clean-room part, but it's not meant for outdoor exposure either.
What the ratings mean for fit
The AC-12 rating of 10 A sets the thermal current limit for resistive loads — don't exceed that. For motor loads, the relevant figure is the AC-3 rating (not explicitly listed here but typically around 4 kW at 400 V for S00 frame). The AC-4 rating of 6.5 A at 400 V is the one to watch for plugging or jogging duty, where the contactor makes and breaks stalled rotor current. The coil draw is 3.3 W both closing and holding — a DC-operated coil that stays cool in continuous service. The mechanical life is rated at 30 million operating cycles typical. That's a high figure — for a contactor switching once per minute, that's about 57 years of continuous operation. Electrical life will be lower and depends on the switched load; the AC-12 figure is the best case. For the main circuit, the recommended fuse for type 2 coordination (no damage to the contactor) is a gL/gG 20 A; for type 1 (contactor may need replacement) it's 35 A.