What it is and what it does
The Siemens 3RT1034-3BE40 is a SIRIUS power contactor in the size S2 frame, designed for switching motor loads in industrial control panels. It is rated for AC-3 duty at 18.5 kW at 500 V and 10 kW at 690 V, which means it handles standard three-phase induction motors up to those power levels without derating for the inrush. The AC-4 rating of 29 A at 400 V covers reversing or inching applications where the contactor makes and breaks the full motor current under load.
Mounting and wiring
Mounts via screw and snap-on onto 35 mm standard mounting rail per DIN EN 50022, and side-by-side mounting is permitted without derating for thermal stacking. The main current circuit uses screw-type terminals accepting 2x (0.75 to 25 mm²) stranded or 2x (0.25 to 2.5 mm²) solid wire. At 40 °C the minimum permissible conductor size is 16 mm², which drives the lug selection for the power feed. The front face carries IP20 protection; the terminal area is IP00, so finger-safe shrouds or a dead-front cover are needed in the panel.
Duty cycles and mechanical life
Mechanical life is typical 10,000,000 operations. Maximum switching rates vary by duty: 1,200 cycles/hour for AC-1 resistive loads, 1,000 cycles/hour for AC-3 motor starting, 750 cycles/hour for AC-2 slip-ring motors, and 250 cycles/hour for AC-4 reversing or plugging. The arcing time is 10 to 15 ms, and the DC operating time (coil pull-in) is 20 to 30 ms — useful to know when sequencing contactors in a star-delta or reversing starter.
Auxiliary contact ratings and environment
Auxiliary contacts are rated for DC switching: 10 A at 24 V, 2 A at 60 V, 1 A at 110 V, and 0.3 A at 220 V. AC ratings include 6 A at 230 V and 3 A at 400 V. The contactor operates from -25 to +60 °C and stores from -55 to +80 °C. Pollution degree 3 means it is suited for industrial environments with conductive pollution, but the IP00 terminals require the panel enclosure to provide the environmental seal.