What it is and what it does
The Siemens 3RT1017-2KB42 is a SIRIUS power contactor in the S00 frame size, designed for switching motor loads and resistive loads in control panels. Its 24 VDC coil draws 2.3 W during both closing and holding, so the control transformer or DC supply doesn't need a big surge margin. The main contacts are rated 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V — enough for small pumps, fans, or conveyor drives up to about 5.5 kW at 400 V in AC-3 duty.
Mounting and integration
Snaps onto 35 mm DIN rail (EN 50022) or screws direct to a backplate. At 45 mm wide and 73 mm deep, it leaves room for auxiliary contact blocks or a surge suppressor on the same footprint. Side-by-side mounting is allowed, so you can gang several contactors without dead space — watch the thermal derating if you pack them tight in a sealed enclosure. Spring-loaded terminals on both main and control circuits accept 2x (0.25…2.5 mm²) solid or stranded, or 2x (24…14 AWG). No screwdriver needed for the wire connection; strip to 8 mm and push in.
What the ratings mean for your panel
Rated operational voltage covers 24 V to 690 V, so the same contactor works across control voltages and motor voltages in mixed panels. The AC-4 rating (8.5 A at 400 V) tells you the contactor can handle frequent inching or plugging — not just steady-state running. Pollution degree 3 means it's suited for industrial environments with conductive dust or condensation, not just clean dry control rooms. Operating temperature range -25 to +60 °C covers most plant-floor conditions without derating.
Short-circuit coordination
With type 2 coordination, the manufacturer specifies a gL/gG fuse of 20 A; type 1 coordination allows up to 35 A. That means you can size the upstream protection to the contactor's rating without over-fusing, keeping fault energy low enough that the contactor stays operational after a short-circuit event (type 2) or is at least safe to replace (type 1).