What this part is and what it does
The Siemens 3RT1934-5BG42 is a SIRIUS magnet coil designed for Size S2 contactors. It operates on a 125 V DC control supply voltage and terminates via spring-loaded connections — a push-in style that eliminates screw torqueing and speeds up panel wiring.
Lifecycle and sourcing reality
This coil is a phased-out product. The manufacturer lists the successor as the SIRIUS 3RT2 series. For a BOM line that still calls out 3RT1934-5BG42, the procurement path is surplus or broker channel — quoted to order against an RFQ. No official cross-reference to a direct drop-in replacement is provided beyond the series-level successor.
What the 125 V DC rating means for fit
The 125 V DC coil voltage is the key fit parameter. If your existing panel supplies 125 V DC control power — common in North American industrial installations with battery-backed DC buses — this coil pulls in and holds the contactor without a dropping resistor or separate DC-DC converter. The spring-loaded terminals accept solid or ferruled stranded wire, same as the 3RT2 series, so re-termination in a retrofit is straightforward.