SIRIUS 3RT1275-6AD36 — Vacuum Contactor, Size S12
The Siemens 3RT1275-6AD36 is a SIRIUS-branded vacuum contactor in the S12 frame size, designed for high-cycle motor switching and furnace/kiln applications where air-break contacts wear too fast. The 42-48 V coil voltage means it drops into 48 VDC control buses common in heavy industrial panels — verify your supply rides above 42 V at the coil terminals under load, because the pickup threshold sits at 80% of rated value (33.6 V), and below that it won't pull in reliably. The main power terminals accept stranded cable from 70 up to 240 mm², so it handles the full range of motor feeder sizes for a S12-frame device.
Duty Ratings & Switching Frequency
This vacuum contactor is rated for 750 operations per hour in AC-3 (squirrel-cage motor starting) and AC-3e duty, and 700 ops/h in AC-1 (resistive load). The AC-4 (plugging/inching) ceiling is 250 ops/h — if your application reverses or jogs the motor frequently, that's the limit to respect for contact life. The arcing time on a vacuum bottle is 10-15 ms, which is tight enough to coordinate with upstream semiconductor fuses but fast enough to limit arc energy on inductive break. Auxiliary contacts are included, rated 10 A at 24 V, 2 A at 48 V and 60 V, and 1 A at 110 V — these are the dry-contact ratings for your PLC input or status feedback loop. The auxiliary switch block is screw-terminal type, same as the coil connection.
If you're comparing against the 3RT1264-6AP36-0KA1 (a similar SIRIUS vacuum contactor in the same S12 frame), the key difference is the coil voltage and the auxiliary contact configuration. The 3RT1275-6AD36 uses a 42-48 V coil, while the 3RT1264-6AP36-0KA1 runs on a different voltage range. They share the same mounting footprint and main power terminal range, so a panel drilled for one can accept the other — but the coil supply must match. No rewiring of the main power circuit is needed; just confirm the control voltage.
Environmental & Mounting
The contactor is not sealed to an IP rating (it's an open-device panel mount), so it's intended for indoor, pollution-degree-2 environments inside a control cabinet. Mounting position flexibility (±22.5° tilt on vertical, or horizontal standing) helps when the backplate is already crowded. Physical envelope: 214 mm high, 160 mm wide, 225 mm deep. The depth is the dimension that typically catches people out during panel layout — 225 mm means you need at least 250 mm clear behind the mounting plate for cable bending radius on the 240 mm² terminals.