The Siemens 3RT1944-5AH21 is a SIRIUS magnet coil designed for Size S3 contactors — the replacement coil that snaps into the contactor's coil terminals when the original fails or the control voltage needs changing. It's a screw-terminal coil rated for 48 V AC at both 50 Hz and 60 Hz, drawing 0.8 to 1.1 A at 50 Hz. The AC control voltage type means it's intended for conventional line-frequency control circuits, not DC or electronic coil drives.
Lifecycle reality — phased out with a successor
This coil is a phased-out product. The manufacturer lists the successor as the SIRIUS 3RT2 series — the newer generation of contactors and their coils. For a BOM that's frozen on the 3RT1 platform, this 3RT1944-5AH21 is the correct drop-in replacement coil. For new designs or panel refreshes, the 3RT2 platform is the forward path.
The coil mounts onto the Size S3 contactor's coil terminals via screw connections — no DIN-rail space consumed beyond the contactor itself. Verify the contactor's coil terminal arrangement matches the screw-terminal format before ordering.