The Siemens 3RT1276-6NB36 is a SIRIUS-branded vacuum contactor in the Size S12 frame — the largest of the standard SIRIUS contactor sizes, built for high-cycle motor switching and furnace/transformer loads where contact erosion from arcing is the main wear mechanism. Vacuum interrupters suppress the arc inside a sealed bottle, so the contactor handles AC-3 duty at up to 750 operating cycles per hour without the contact maintenance a conventional air-break contactor needs. Coil pull-in is rated 21–27.3 VDC, screw-type terminals on the magnet coil; the main power circuit accepts stranded cable up to 240 mm² per lug, which puts it in the class for motors in the 200–400 kW range depending on voltage and duty.
Mounting and panel integration — Size S12 envelope
The contactor measures 225 mm deep, 160 mm wide, 214 mm tall. That 225 mm depth is the dimension to check against the back panel or enclosure door clearance — it's deeper than a standard IEC contactor because the vacuum bottle assembly and the arc-chamber stack add axial length.
Coil and control circuit — screw terminals, DC pick-up
The magnet coil uses screw-type terminals, rated 21–27.3 VDC. The coil's initial value factor is 0.8, full-scale value 1.1 — these are the operating tolerances for the control voltage. Auxiliary switch is included (screw-type terminals on the aux block). Control wiring accepts solid or stranded conductors: 2× (0.5–1.5 mm²), 2× (0.75–2.5 mm²), max 2× (0.75–4 mm²).