What this SIRIUS Size S3 contactor does
The Siemens 3RT1045-1AL20-ZW96 is a SIRIUS power contactor in Size S3, designed for switching motor loads and resistive loads in industrial control panels. It carries a 45 kW rating at 500 V AC-3, which is the standard duty for squirrel-cage motors — that's the number that matters for sizing a motor starter. At 690 V AC-3 it's rated 21.1 kW, so the same contactor can handle a higher-voltage motor at reduced power. The contactor mounts on 35 mm or 75 mm DIN rail via screw and snap-on fastening, which is the standard for European-style panels. At 70 mm wide and 146 mm tall, it fits a standard 8-module DIN-rail slot — no surprises for the panel builder laying out a row of starters. Termination is screw-type on the main current circuit, accepting solid conductors up to 4 mm² on the control side and stranded up to 50 mm² on the power side. That covers most motor feeds up to 45 kW without needing lug adapters.
Duty cycle and thermal limits
The mechanical life is rated at 10,000,000 operations typical, which is standard for a SIRIUS Size S3 contactor in cyclic applications like conveyor or pump control. The electrical endurance depends on the duty category: AC-3 allows up to 1,000 switching cycles per hour, while AC-4 (plugging/inching) drops to 300 cycles per hour. For resistive loads (AC-1) it's 900 cycles per hour. Operating temperature range is -25 to +60 °C, with storage from -55 to +80 °C. That covers most indoor panel environments, but if the panel sits in a non-conditioned space near a furnace or in a desert plant, the +60 °C ceiling is the limit — no derating curve is stated here, so keep ambient below that. Degree of pollution 3 means it's rated for conductive pollution environments — typical for industrial panels where some dust and humidity are present. The front is IP20 with the cover/box terminal installed; the terminal area itself is IP00, so live parts are exposed when the panel door is open.
Coil and control circuit
The coil operates on 50/60 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 ±20% / +10% range — the coil will pick up reliably even if the control transformer sags under load. Arcing time is 10 to 15 ms, and the AC operating time is 10 to 25 ms. The contactor is rated for 24 V DC auxiliary switching at 10 A, stepping down to 0.3 A at 220 V DC. That covers most PLC output cards and relay interfaces. For AC auxiliary loads at 230 V it's rated 6 A, and at 400 V it's 3 A.