What this SIRIUS S0 contactor does in a panel
The Siemens 3RT1024-1BD44 is a SIRIUS power contactor in the S0 frame, built for switching motor loads and resistive loads in control panels. The 42 VDC coil pulls in at 5.4 W and holds at the same 5.4 W — no power drop after pick-up, so the DC supply needs to sustain that continuously. Rated for AC-4 duty at 12.5 A on 400 V, meaning it handles reversing or inching (plugging) of squirrel-cage motors at that current, which is the punishing switching condition. For AC-2 (slip-ring motor starting) it's rated 5.5 kW at 400 V. The AC-12 rating of 10 A covers control-circuit loads like PLC outputs or relay coils. Screw terminals on the main circuit accept up to 2x 10 mm² stranded or 1x 8 AWG. Mounting is screw or snap-on onto 35 mm DIN rail per EN 50022. Side-by-side mounting is allowed with zero side clearance — the 45 mm width per pole stacks tight. Pollution degree 3 (conductive pollution, typical in industrial enclosures) is rated, and the front face carries IP20 while the terminals are IP00 (finger-safe only when wired into an enclosure). Ambient operating range is -25 to +60 °C, altitude up to 2000 m.
Coordination and protection
For Type 2 coordination (no damage to the contactor after a short-circuit) the required upstream fuse is gL/gG 25 A. For Type 1 coordination (contactor may need replacement after a fault) the fuse can be 63 A gL/gG. The mechanical life is 10 million switching cycles. Two instantaneous auxiliary contacts are built in (no separate aux block needed for basic signaling).