What it is and what it fits
The Siemens SIRIUS 3RT1934-5AC21 is a replacement magnet coil for Size S2 contactors in the SIRIUS family. It's the part that pulls the contactor in — rated for 24 V AC control supply at both 50 Hz and 60 Hz, with a screw-terminal connection for the control wiring. The coil's operating range at 50 Hz is 0.8 to 1.1 times the rated voltage, meaning it'll pull in reliably down to about 19.2 V and hold up to 26.4 V before the thermal limit starts to matter.
What it connects to
This coil mounts onto SIRIUS Size S2 contactors via screw terminals. The contactor frame itself snaps onto a 35 mm DIN rail per EN 50022, so the coil replacement happens in-panel without pulling the whole contactor. The 24 V AC control voltage is common across European panel designs — it shares the same transformer tap as the PLC and HMI supplies in most cabinets.