What this part is and what it fits
The Siemens SIRIUS 3RT1934-5BF42 is a replacement magnet coil for Size S2 contactors in the SIRIUS family, wound for 110 V DC control voltage and terminated with spring-loaded (cage-clamp) connections. Size S2 covers contactors rated for motor currents roughly in the 38–65 A AC-3 range at 400 V — think medium conveyors, pump starters, compressor duty. The coil itself is the replaceable electromagnet that pulls the contactor in; when a coil fails open or shorts, you swap this rather than the whole contactor assembly.
Lifecycle reality — phased out, successor known
For a BOM that still calls out 3RT1934-5BF42, sourcing is through the independent channel — quoted to order against an RFQ. If you are designing a new panel or have the flexibility to change the contactor base, the 3RT2 series is the official forward path.
What the 110 V DC rating means for the panel
The 110 V DC control supply is common in North American industrial control panels with DC control buses, and in some European process plants that run 110 V DC for reliability over long cable runs. The spring-loaded terminals accept solid or ferruled stranded wire without needing a screwdriver torque check — faster termination and less prone to vibration loosening than screw-type. Because this is a DC coil, the holding power is continuous; there is no AC hum or shading ring to fail. Verify your DC supply can deliver the inrush without droop — a 110 V DC coil pulling in can dip a marginal power supply below the dropout threshold of other devices on the same bus.