The Siemens 3RT1275-6AT36 is a SIRIUS-branded vacuum contactor, design size S12. Vacuum contactors are specified for switching medium-voltage motor loads where arc extinction in air is insufficient — the vacuum bottle quenches the arc in a sealed chamber, giving a clean break with minimal contact erosion. The rated voltage is 575... 600 V AC, which places it in the low-voltage range but at the upper end, often used in 600 V class industrial distribution in North America and 575 V Canadian mining or heavy industrial installations. The coil circuit uses screw-type terminals, accepting solid or stranded conductors: 2x (0.5... 1.5 mm²), 2x (0.75... 2.5 mm²), max. 2x (0.75... 4 mm²). The main power circuit accepts stranded conductors from 70 up to 240 mm² — that is substantial cable, consistent with the current-carrying capacity of a size S12 frame. Pickup voltage is 0.8 of rated value; dropout is not stated but typically around 0.6–0.7 for this class.
Maximum switching rates vary by duty category: at AC-1 (resistive loads) 700 operations per hour; at AC-2 (slip-ring motors) 250/h; at AC-3 (squirrel-cage motors, starting only) 750/h; at AC-4 (plugging, inching) 250/h; and at AC-3e (enhanced AC-3) also 750/h. The AC-3 and AC-3e rates are the ones that matter for most motor-starting applications — 750 ops/h means a cycle time of about 4.8 seconds, which is fast enough for conveyor or pump cycling.
Mechanical Life and Environmental Limits
That is a high count, consistent with vacuum contactors that see little contact wear. Fastening is by screw fixing through one 11 mm diameter hole.
An auxiliary switch is included. Its rated values: 10 A at 24 V, 2 A at 48 V, 2 A at 60 V, 1 A at 110 V. These are the continuous current ratings at the stated DC voltages — useful for control circuit design. The full-scale overload factor is 1.1, meaning the contactor can sustain 110% of its rated current for a defined period (typically 1 hour per IEC 60947).