The Siemens 3RT1647-1AU01 is a SIRIUS capacitor contactor built for AC-6 duty, switching capacitor banks up to 50 kVAr at 400 V. That AC-6 rating is what matters here — it's not a general-purpose contactor; it's designed for the high inrush current and repetitive switching of power-factor-correction capacitors. The 240 V AC 50 Hz coil and 3-pole main contacts come in the Size S3 frame, which means it's a physically larger contactor than the S0 or S00 sizes you'd see for motor starting at similar currents.
Lifecycle and sourcing reality
The lifecycle stage is listed as current, but the description flags this as a phased-out product with the successor being the SIRIUS 3RT2 series. The substance prohibitance date of 05/01/2012 aligns with the transition to RoHS-compliant production — not an obsolescence trigger by itself, but it tells you this part number predates the 3RT2 generation. For a BOM line that's already qualified, the 3RT1647-1AU01 remains a valid spare; the 3RT2 successor will have different dimensions and coil options, so a drop-in swap without panel rework is unlikely. We source this against an RFQ through independent distribution channels.
What the AC-6 rating means on the panel floor
AC-6 duty under IEC 60947-4-1 covers switching of capacitor banks. The 50 kVAr at 400 V figure tells you the maximum reactive power this contactor can handle — pushing it beyond that risks contact welding from the capacitor's charging current. The S3 frame uses screw-type terminals on the main circuit; wire sizes up to 35 mm² are permissible at 40 °C ambient. The coil draws 15 W holding power at DC, so if you're running a 240 V AC coil through a control transformer, factor that into the VA budget.