SIRIUS 3RT1035-3BD40 — Power Contactor, Size S2
The Siemens 3RT1035-3BD40 is a SIRIUS power contactor in the Size S2 frame, rated 18.5 kW at 400 V in AC-2 duty and 22 kW at 500 V — a common pick for switching slip-ring motor loads or medium-duty compressors where the AC-2 rating governs the thermal capacity, not the AC-3 number.
Ratings That Drive the Selection
AC-4 at 400 V is rated 35 A — that is the reversing / plugging / inching duty cycle, where the contactor sees make-and-break at locked-rotor current. If your application cycles the motor direction or jogs it under load, the AC-4 rating is the one that keeps the contacts from welding. The 690 V rating drops to 11.4 kW — expect that derating when the line voltage climbs above 500 V. The 42 V rated value is the coil voltage; verify your control transformer matches before wiring. Main current circuit uses screw-type terminals, accepting solid conductors 2x (0.25 … 2.5 mm²) and stranded 2x (0.75 … 25 mm²). At 40 °C the minimum permissible cross-section is 16 mm² — that is the thermal floor for full-rated current without exceeding the terminal temperature rise.
Front face carries IP20 (finger-safe); the terminal area is IP00 — panel builders should plan for a cover or distance guarding above the terminals in the enclosure layout.
Width 55 mm, height 112 mm, depth 130 mm. Side-by-side mounting is permitted, so multiple contactors can share the same DIN rail segment without a mandatory air gap — useful for compact motor control centers. Solid or stranded wire sizes for auxiliary circuits: 2x (0.75 … 16 mm²). The mechanical switching frequency at AC-3 is 1 000 operations per hour; at AC-4 it drops to 300 per hour — plan the cycle count against the application profile.