What it is and what it does
The Siemens 3RT1017-2KF42 is a SIRIUS power contactor in size S00, designed for switching motor loads and resistive loads in control panels. It carries a 110 VDC coil with a closing and holding power of 2.3 W each, and spring-loaded terminals on both the main and auxiliary circuits — no screwdriver needed for wiring, which speeds panel assembly and reduces torque-verification steps. Rated for AC-2 duty at 400 V at 5.5 kW, it handles slip-ring motor switching where moderate inrush and repetitive starting are expected. For AC-4 duty (plugging, inching) at 400 V, the maximum operational current is 8.5 A — the rating that governs reversing or jogging applications. The AC-12 maximum current of 10 A covers resistive loads like heaters or lighting banks.
Mounting and integration
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022. The 45 mm width and 73 mm depth fit standard panel layouts; side-by-side mounting is permitted without derating, so you can gang multiple contactors on the same rail for multi-motor groups. Pollution degree 3 rating means it tolerates conductive dust and humidity typical of industrial enclosures not kept at climate-controlled conditions. Spring-loaded terminals accept 2x (0.25 to 2.5 mm²) solid or stranded wire, or 2x (24 to 14 AWG) for both main and auxiliary circuits. The IP20 front protection means the contactor is safe for finger-probe access inside a closed panel; it is not rated for washdown or outdoor exposure without an additional enclosure.
Coordination and protection
For Type 2 coordination (no damage to the contactor under short circuit), the required upstream fuse is gL/gG 20 A. For Type 1 coordination (contactor may need replacement after a fault), the fuse rating is gL/gG 35 A. The built-in varistor surge suppressor on the coil handles voltage spikes from the DC switching — no external suppressor needed for most applications.