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.
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.
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 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.