What this part is and where it fits
The Siemens 3RT1944-5AC21 is a SIRIUS magnet coil designed for Size S3 contactors. It operates on 24 V AC control voltage at both 50 Hz and 60 Hz, with a screw terminal connection. The coil draws an inrush current of 0.8 to 1.1 A at 50 Hz, which is the peak current the control transformer or PLC output must handle during pickup.
What the ratings mean for fit
The 0.8 to 1.1 A at 50 Hz is the inrush (closing) current, not the holding current. The holding draw is significantly lower — the coil's apparent holding power is around 12.5 VA on the S2-size sibling (3RT1036-1AB00), and the S3 coil here will be similar. This matters when sizing the control transformer: the inrush pulse is brief but must not drop the supply voltage below the coil dropout threshold (typically 18 V AC for a 24 V nominal coil). The 24 V AC rating at both 50 Hz and 60 Hz means the coil impedance is designed for either line frequency without derating. No need to swap coils when moving between 50 Hz and 60 Hz grids.
Panel integration note
The coil mounts on a Size S3 contactor via screw terminals. The contactor itself snaps onto a 35 mm DIN rail per EN 50022. When replacing a failed coil in an existing panel, confirm the contactor frame size — the 3RT1944-5AC21 fits only S3 frames, not S0 or S2. The screw terminal accepts 2x (0.5 to 1.5 mm²) solid or stranded, or 2x (0.75 to 2.5 mm²) with ferrule.