Siemens SIRIUS 3RT2045-1AH00 — S3 Power Contactor, 77 A AC-3
The Siemens SIRIUS 3RT2045-1AH00 is a S3-frame power contactor rated for 77 A at 400 V in AC-3 duty — the motor-switching current that governs real-world sizing for induction motors up to that load. The S3 frame (Size 3) is the mechanical envelope; it carries screw-type main contact terminals accepting 2.5 to 16 mm² solid or 6 to 70 mm² stranded conductors, so it lands comfortably on a 50 A to 100 A motor branch circuit without adapter lugs. Mounting is screw-and-snap-on to 35 mm DIN rail per DIN EN 60715, with a ±180° rotation allowance on vertical surfaces and ±22.5° tilt forward/backward — useful when the panel layout forces an unconventional orientation. The contactor occupies 70 mm width, 140 mm height, 152 mm depth, so it fits a standard S3 footprint in most motor control centers. An auxiliary switch is built in (10 A at 24 V, derating to 0.3 A at 220 V), covering feedback to a PLC or holding-circuit interlock without an add-on block.
Installation & Wiring
Main power terminals accept solid conductors 2.5 to 16 mm² or stranded 6 to 70 mm² — use ferruled stranded for the upper range to avoid strand fanning under the screw head. Auxiliary terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded, suitable for daisy-chaining control wiring. These are the minimum air gaps to adjacent metalwork or enclosures for rated insulation; crowding the contactor reduces arc-chamber venting and may shorten contact life on high-breaking-capacity faults.
Switching Performance & Duty Cycles
Maximum switching rates: AC-1 (resistive) 900 cycles/h, AC-2 (slip-ring motor) 400 cycles/h, AC-3 (squirrel-cage motor) 1 000 cycles/h, AC-4 (plugging/inching) 300 cycles/h. The AC-3e rating also sits at 1 000 cycles/h, confirming the contactor handles standard motor starts at full load without thermal overload. Arcing time is 10 to 20 ms; operate time at AC is 10 to 21 ms. These are the contactor's inherent switching speeds — fast enough for most motor control, but not suitable for precision timing applications where a solid-state relay would be required. Auxiliary contact ratings cover DC loads: 10 A at 24 V, 2 A at 48 V, 2 A at 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V, 3 A at 400 V, 0.8 A at 440 V. The 15 hp rating at 230 V applies to the main contacts in AC motor duty.