The Siemens 3RT1275-6AU36 is a SIRIUS vacuum contactor in Size S12. The vacuum arc-quenching chamber keeps contacts clean over the rated mechanical life of 10,000,000 operations. Rated coil voltage is 240-277 V AC, and the coil termination is screw-type terminals. The auxiliary switch is included, which saves ordering a separate block for basic feedback or status indication.
The power circuit accepts stranded cable from 70 to 240 mm² — that's a heavy lug range, consistent with the Size S12 frame's current-handling capability. The control circuit solid/stranded range is 0.5 to 4 mm², which covers standard control wiring. If you're terminating fine-stranded control wire, note the 0.5 mm² minimum; don't go smaller. Switching frequency limits: 750 operations per hour at AC-3 (motor starting), 700 at AC-1 (resistive), and 250 at AC-2 or AC-4 (slip-ring motor or plugging duty). The AC-3e rating also maxes at 750 ops/h. Auxiliary contact ratings: 10 A at 24 V, 2 A at 48 V, 2 A at 60 V, 1 A at 110 V. These are the make/break capacities for the built-in auxiliary switch — useful for interlocking or PLC input feedback. If you need more than one auxiliary contact, you'll add a separate block. The power factor is 0.9 at both 50 and 60 Hz.
Fastening is screw fixing through a single 11 mm hole. The contactor dimensions are 225 mm deep, 160 mm wide, 214 mm high. That forward clearance is the one to watch — 20 mm means the arc chute and coil cover need that space for cooling and access. The Size S12 frame is a standard Siemens contactor footprint; if you're replacing a similar SIRIUS unit, the mounting hole pattern and busbar connections should align. The arcing time is 10-15 ms, and the dropout times at both AC and DC are 60-100 ms — that's the interval before the auxiliary contacts change state after coil de-energization.