What this part is and what it does
The Siemens SIRIUS 3RT1935-5AK61 is a replacement magnet coil for Size S2 contactors in the SIRIUS family. It provides the electromagnetic force to pull in and hold the contactor armature, rated for a control supply of 110 V AC at 50 Hz or 120 V AC at 60 Hz. The coil draws a holding power in the range of 0.8 to 1.1 at 50 Hz, which is the power needed to keep the contactor closed once it has picked up.
Fit and integration
The coil mounts onto a Size S2 SIRIUS contactor frame via screw terminals. The control voltage is AC only — 110 V at 50 Hz or 120 V at 60 Hz — so verify your control transformer taps before installing. The coil's holding power (0.8 to 1.1 at 50 Hz) is low enough that the control transformer can typically share a circuit with the PLC output driving it, but check the inrush at pickup if the transformer is lightly sized.