SIRIUS S3 power contactor – panel-fit and wiring
The Siemens SIRIUS 3RT1045-1AL20 is a size S3 power contactor rated for motor loads up to 45 kW at 500 V and 21.1 kW at 690 V. It snaps onto 35 mm or 75 mm DIN rail and measures 70 mm wide by 146 mm tall by 139 mm deep — a standard S3 footprint that fits most motor control centre buckets and enclosure backplates without crowding adjacent devices. Main power wiring accepts solid or stranded conductors up to 50 mm² (stranded) or 4 mm² per solid pair, with screw-type terminals that are field-friendly for panel builders. The auxiliary circuit handles 10 A at 24 V, 6 A at 230 V, and 3 A at 400 V — enough for most PLC or relay interface loads.
Switching performance and lifecycle
Electrical switching frequency varies by duty: 1 000 cycles/hour under AC-3 (motor starting), 900 under AC-1 (resistive), 400 under AC-2 (slip-ring motor), and 300 under AC-4 (plugging / inching). Arcing time sits between 10 and 25 ms depending on the load — standard for a contactor this size. The contactor is rated for both 50 Hz and 60 Hz supplies, with an operating range of 0.8 to 1.1 times rated voltage at 50 Hz and 0.85 to 1.1 at 60 Hz. Side-by-side mounting is allowed, so multiple units can be ganged without derating — useful for compact motor starter assemblies.
This part carries a current-production lifecycle status. No official successor has been announced — the 3RT1045-1AL20 remains the active S3 screw-terminal variant in the SIRIUS family.