What it is and what it does
The Siemens 3RT1015-2BW42 is a SIRIUS power contactor in frame size S00, designed for switching motor loads and resistive loads in control panels. The 48 V DC coil draws 3.3 W during closing and holding, so the control transformer or power supply must be sized for that continuous draw — no inrush peak to worry about with DC coils, but verify the supply can sustain the holding power without droop. Rated operational current at AC-12 (resistive) is 10 A; for motor duty, AC-2 at 400 V delivers 3 kW, and AC-4 at 400 V is rated 6.5 A. That AC-4 figure is the one that governs reversing or plugging applications — if your line cycles the contactor under load, size on AC-4, not AC-3. Mechanical endurance is listed at 30 000 000 cycles typical, which is high for the S00 frame — expect the electrical life to be lower under full load, but the mechanism itself will outlast most panel refreshes.
Mounting and wiring
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022. The 45 mm width and 60 mm height leave room for adjacent devices in a crowded enclosure; side-by-side mounting is permitted without derating if ambient stays within -25 to +60 °C. Main and auxiliary/control circuits use spring-loaded terminals accepting 2x (0.25 to 2.5 mm²) solid or stranded, or 2x (24 to 14 AWG). No screwdriver torque to check — strip to 8 mm, push in. The IP20 rating on the front and terminals means finger-safe for panel builders but not for wet or dusty environments.
Coordination and protection
For type 2 coordination (no damage to the contactor under short circuit), the evidence specifies a gL/gG fuse rated 20 A. For type 1 coordination (contactor may need replacement after fault), use 35 A gL/gG. The degree of pollution is 3, so in dirty or conductive-dust environments, consider a conformal coating or a higher-IP enclosure.