The Siemens SIRIUS 3RT5975-5AB31 is a replacement magnet coil for size S12 contactors in the SIRIUS family. This means the same coil can be wired into a panel running either an AC control transformer or a DC supply bus without swapping parts.
This coil is sized for the S12 contactor frame — the same physical footprint as the 3RT10 and 3RT20 SIRIUS contactors in that size class. When replacing a failed coil on an existing S12 contactor, verify the control voltage matches the 26 V AC/DC rating before energizing. The AC/DC designation means the coil's suppression circuitry handles both waveforms, but polarity matters on the DC side: observe the marking on the coil terminals.