What it is and what it does
The Siemens 3RT2017-2KB42-0LA0 is a SIRIUS power contactor in the compact Size S00 frame (45 mm wide, 70 mm tall, 121 mm deep). It's designed for switching DC loads up to 10 A at 24 V, with a 24 VDC coil that picks up at 70% of rated voltage. The spring-type terminals on the coil side accept solid or stranded wire up to 4 mm². This contactor is a standard building block for DC control circuits in industrial panels — think conveyor brakes, solenoid valves, or DC motor contactors in a 24 VDC control architecture. The Size S00 footprint means it fits tightly on a 35 mm DIN rail (per DIN EN 60715), saving panel width for other components.
DC switching ratings — what they mean for your circuit
The key spec for a DC contactor is the current it can break at a given voltage, because DC arcs are harder to extinguish than AC. At 24 VDC, the 3RT2017-2KB42-0LA0 is rated for 10 A. At 48 V and 60 V, that drops to 2 A; at 110 V it's 1 A; at 220 V it's 0.3 A. These are the DC-1 (resistive load) ratings — if you're switching inductive loads (DC-3 or DC-5), expect to derate further or add a snubber. The contactor also carries AC ratings for motor starting: 3 A at 400 V AC-3, 11 A at 480 V, and 11 A at 600 V. That 11 A at 480 V is the figure to watch if you're using this on a 480 VAC motor branch — it's the AC-3 rating that governs contactor life under motor switching.
Mounting and wiring
Mounts via screw or snap-on to 35 mm DIN rail. The mounting position is flexible: ±180° rotation on a vertical surface, and can be tilted forward/backward by ±22.5° on a vertical surface. Keep 10 mm clearance above and below, 6 mm at the sides for arc dissipation and airflow. Coil terminals are spring-type, accepting 2x (0.5 to 1.5 mm²), 2x (0.75 to 2.5 mm²), or 2x 4 mm² solid or stranded. Main contact wiring accepts 2x (0.5 to 4 mm²). No screwdriver needed for the coil connection — just strip to 8 mm and push in.
Lifecycle and sourcing reality
For a BOM line that calls out 3RT2017-2KB42-0LA0, the fit is straightforward: Size S00, 24 VDC coil, spring terminals. If you're stocking spares for a panel that uses the 3RT2326-1BK80 (a larger frame), this won't drop in without rewiring — different footprint and coil voltage. This is the part to order when the BOM says 3RT2017-2KB42-0LA0.