What it is and what the ratings mean
The Siemens SIRIUS 3RT1034-1XB44-0LA2 is a size S2 power contactor with a 24 VDC coil, rated for motor switching at 18.5 kW at 500 V AC-3 and 10 kW at 690 V AC-3. The AC-3 rating is the one that governs real motor duty — the contactor is sized for that load, not the higher AC-1 resistive current. It carries 2 instantaneous auxiliary contacts rated 10 A at 24 V and 6 A at 230 V, which is enough to signal a PLC input or drive a small indicator lamp without an interposing relay. The coil pickup-to-dropout ratio is 0.7, meaning it holds in at around 16.8 V and drops out below that. Dropout time on DC is 20 to 30 ms — fast enough for most E-stop circuits but not a safety contactor; that's a separate device. Arcing time runs 10 to 15 ms, which is typical for this frame class. Mechanical life is rated 10 million operations. Switching frequency tops out at 1200 ops/h in AC-1, 1000 in AC-3, and 250 in AC-4 — that last one is the one to watch if you're jogging or inching a motor under load; it's the contact wear limit.
Mounting and integration
Mounts via screw and snap-on onto a 35 mm DIN rail per EN 50022. Side-by-side mounting is allowed — no derating gap required between units, which saves rail space in a dense panel. Clearance to grounded metal is 10 mm in all directions (up, down, forward, side). Main circuit terminals are screw-type, accepting stranded wire up to 25 mm² or solid/stranded combinations up to 16 mm² at the AC-1 maximum rating. Auxiliary terminals accept 2x (0.5 to 1.5 mm²) solid or 2x (0.75 to 2.5 mm²) stranded, with a maximum of 2x (0.75 to 4 mm²). That covers standard control wiring. Overall dimensions are 55 mm wide, 142 mm high, 179 mm deep — fits a standard 200 mm deep enclosure. Operating temperature range is -40 to +70 °C, storage -55 to +80 °C. The storage limit governs handling and shipping, not running. If the panel ambient hits 70 °C, the contactor is still within its rated band — no forced derating needed.