What this part is and what it does
The Siemens 3RT1945-5AP01 is a SIRIUS-branded magnet coil, the electromagnetic actuator that pulls in the contactor armature when energized. It is sized for SIRIUS size S3 contactors and terminates via screw terminals. The control voltage is 230 V AC at 50 Hz, with an operating range of 0.8 to 1.1 times that nominal voltage — meaning the coil will reliably pick up between roughly 184 V and 253 V AC, and will hold in down to about 184 V. This is the replacement coil for a failed or missing coil on an existing S3 contactor, not a standalone contactor itself.
Lifecycle and sourcing reality
This part is a phased-out product. The manufacturer's official successor is the SIRIUS 3RT2 series. For a buyer with a BOM line or a panel that needs this exact coil, the original 3RT1945-5AP01 is sourced through independent distribution channels — quoted to order against an RFQ. Availability and current pricing are confirmed at quote time. If your design is still open, the 3RT2 series is the direct replacement path; if you are repairing an existing S3 contactor panel, the 3RT1945-5AP01 remains available through the surplus and broker network.
Fit and integration
This coil mounts directly onto SIRIUS size S3 contactor frames. The screw terminals accept the same wiring as the original coil — no adapter or re-termination needed. It is a drop-in swap for an existing S3 contactor that has lost its coil or needs a different control voltage. The coil's operating range (0.8 to 1.1 x 230 V AC) means it will function correctly on a 230 V AC control circuit with typical voltage sag, but verify your control transformer is sized for the inrush (pick-up) VA of the coil — the S3 coil draw is higher than the S00 or S0 sizes.