SIRIUS S3 power contactor — 45 kW at 500 V, screw terminals, snap-on DIN rail
The Siemens 3RT1045-1AD20 is a SIRIUS S3 power contactor rated for 45 kW at 500 V 50 Hz and 21.1 kW at 690 V, making it the motor-switching choice for medium-horsepower induction motors in the 50–75 kW class at 400 V. The contactor snaps onto 35 mm or 75 mm standard mounting rail, and side-by-side mounting is permitted — no derating gap required between units on the rail.
The AC-3 switching frequency is rated at 1 000 operations per hour maximum, which covers most conveyor and pump cycling. AC-4 (plugging/reversing) is limited to 300 ops/h — if your application jogs or reverses frequently, that's the duty cycle to watch. Mechanical life is typical 10 000 000 operations, so the contactor itself outlasts most panel refreshes. The coil operates across 0.8 to 1.1 times rated voltage at 50 Hz and 0.85 to 1.1 at 60 Hz, with pick-up time 10–25 ms and arcing time 10–15 ms — consistent with a standard AC coil contactor. Auxiliary contact ratings: 10 A at 24 V, 6 A at 230 V, 3 A at 400 V, 0.3 A at 220 V DC. The auxiliary accepts solid conductors 2x 0.5–1.5 mm² or 2x 0.75–2.5 mm², max 2x 0.75–4 mm² — standard for control wiring. The 24 V DC rating of 10 A is notably high, useful for pilot-duty control circuits without an intermediate relay.
Dimensions: 146 mm height, 70 mm width, 139 mm depth. The S3 frame is the mid-size in the SIRIUS contactor family — expect to allocate roughly 150 mm of DIN rail height per unit. Screw terminals on the main circuit accept 2x 10–50 mm² stranded; auxiliary terminals accept 2x 0.5–1.5 mm² solid. Side-by-side mounting is permitted, so no spacing between units on the rail is required for thermal derating.