What it is and what it does
The Siemens SIRIUS 3RT1035-1BB40-ZW96 is a Size S2 power contactor from the SIRIUS family, built for switching three-phase motors and resistive loads in control panels. Its 24 VDC coil pulls in reliably, and the AC-3 rating of 22 kW at 500 V tells you it handles induction motors up to that power without welding the contacts. At 690 V it's still good for 11.4 kW AC-3 — useful where the line voltage runs higher than the usual 400 V. The AC-4 rating of 35 A at 400 V matters if you're jogging or inching the load — that's the reversing/plugging duty cycle where the contacts break full motor current. For resistive heating or lighting (AC-1) it'll cycle 1 200 operations per hour; AC-3 motor starting gets 1 000 ops/hr; AC-4 jogging drops to 300 ops/hr. That's the thermal limit of the S2 frame, not a software cap.
Mounting and wiring
Mounts via screw or snap-on onto 35 mm DIN rail per DIN EN 50022 — the standard rail in every panel I've opened. Side-by-side mounting is allowed, so you can pack contactors tight on the rail without derating, as long as you respect the ambient temperature range of -25 to +60 °C during operation. The screw-type main circuit terminals accept solid wire from 2x (0.5 to 1.5 mm²) up to 2x (0.75 to 4 mm²), and stranded from 2x (0.75 to 25 mm²). At 40 °C the minimum permissible cross-section is 16 mm² — that's your feeder wire for the full rated current. IP20 on the front face, IP00 at the terminals, so it's protected against finger contact on the cover but the lug area is live; keep tools and fingers clear.
Lifecycle and compliance
Mechanical life is typical 10 million operations. The coil operates on 24 VDC with an arcing time of 10 to 15 ms and a dropout time of 20 to 25 ms — fast enough for most safety circuits, but verify your PLC cycle time if you're monitoring the auxiliary contacts for feedback.