What it is and what it does
The Siemens 3RT1035-1AN24 is a SIRIUS power contactor in Size S2, designed to switch motor loads in control panels. Its headline rating is 18.5 kW at AC-2 duty at 400 V — that's the current it can make and break for slip-ring motor starting, where the load is inductive but not as severe as full plugging. For AC-3 squirrel-cage motors, the rating is 22 kW at 500 V and 11.4 kW at 690 V, covering the common European 400 V and 690 V industrial supplies. The contactor mounts via screw and snap-on onto 35 mm standard mounting rail per DIN EN 50022, so it drops straight into any IEC-style panel. At 55 mm wide, 112 mm tall, and 164 mm deep, it fits a standard S2 footprint — plan for the depth when routing wires behind the DIN rail. Side-by-side mounting is permitted, so you can gang multiple contactors without a gap, but watch the thermal derating if you pack them tight at full load. The main current circuit uses screw-type terminals, accepting solid wire up to 2x 4 mm² and stranded up to 2x 25 mm². That's enough for the full-rated motor cable on a 22 kW drive — just make sure the ferrule or ring tongue matches the screw clamp range. The front is IP20 (finger-safe), the terminal area is IP00 (open), so the panel enclosure provides the overall IP rating.
What the ratings mean for fit
The AC-1 maximum operating rate is 1200 cycles per hour — that's for resistive loads like heaters, where the contactor sees minimal arcing. AC-3 drops to 1000 cycles per hour (standard motor starting), and AC-4 is 300 cycles per hour (plugging or inching). If your application needs frequent jogging, the AC-4 limit is the one that governs contact life, not the AC-3 number. Mechanical life is rated at 10 million operations typical. That's the mechanism without load — electrical life will be lower depending on the switching duty and current. For a conveyor line cycling once per minute, the mechanical life alone gives about 19 years of continuous operation. Pollution degree 3 means the contactor is rated for conductive pollution or dry non-conductive pollution that becomes conductive due to condensation — typical for industrial control panels not in a cleanroom. Operating temperature range is -25 to +60 °C, storage is -55 to +80 °C. If your panel sits in an unheated warehouse in winter, the storage range covers it; the operating range covers most plant-floor conditions.
Wiring and integration notes
The coil operates at 50 Hz and 60 Hz, with a voltage tolerance of 0.8 to 1.1 times rated at 50 Hz and 0.85 to 1.1 at 60 Hz. That's a standard ±10% band with a slight asymmetry at 50 Hz — the coil holds in at 80% of nominal, drops out below that. Arcing time is 10 to 15 ms, and the AC switching time is 7 to 20 ms, which matters for coordination with upstream breakers or fuses. Auxiliary contact ratings: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 0.3 A at 220 V DC. The DC ratings drop fast with voltage — at 220 V DC it's only 0.3 A, so don't plan to switch a DC solenoid directly without checking the load current against the curve.