What this contactor is and what it does
The Siemens 3RT1035-1BB44-0AA1 is a SIRIUS power contactor in the Size S2 frame, designed to switch three-phase motor loads in control panels. Its 24 V DC coil pulls in reliably across the full operating range, and the screw-type main circuit terminals accept stranded conductors up to 25 mm² — enough for the 22 kW motor it's rated to switch at 500 V AC-3. The 179 mm depth fits standard 400 mm deep enclosures; width is 55 mm, height 112 mm, so it occupies one 55 mm-wide slot on a DIN rail.
What the key ratings mean when you're wiring it in
AC-3 at 400 V is the standard motor-switching duty: this contactor handles 22 kW at 500 V and 11.4 kW at 690 V. Those numbers mean it can start and stop a squirrel-cage induction motor under full load — the contacts are sized for the inrush and the arc is quenched fast enough. At AC-4 (plugging, inching, reversing) it's rated 35 A at 400 V, which is the more punishing duty cycle: the contactor makes and breaks stalled-rotor current, so the 35 A figure is what governs if you're doing jogging or reversing. The mechanical life is 10 million operations typical, and the maximum switching rate at AC-3 is 1 000 cycles per hour — that's one every 3.6 seconds, which covers most conveyor and pump cycling. The built-in auxiliary contact block switches at 24 V DC up to 10 A, and derates to 0.3 A at 220 V DC — useful for PLC input signals or interlocking relays in the same panel. Pollution degree 3 means it's rated for industrial environments where conductive dust or condensation is present; the front face is IP20 (finger-safe), the terminal area is IP00 (tool-safe only). Side-by-side mounting is allowed, so you can pack multiple contactors on the same rail without derating, as long as you respect the ambient temperature limit of 60 °C during operation.
Mounting and wiring
Snap-on mounting onto 35 mm DIN rail per EN 50022 is the primary method; screw fixing is also possible. The main circuit terminals are screw-type, accepting solid conductors 2x (0.5…1.5 mm²) up to 2x (0.75…4 mm²), and stranded 2x (0.75…25 mm²). At 40 °C ambient, the minimum permissible cross-section is 16 mm² for full rated current. The coil terminals are separate and accept 2x (0.5…1.5 mm²) solid or 2x (0.75…2.5 mm²) stranded. No special tools beyond a screwdriver and a wire stripper — fix it where it sits.