The Siemens SIRIUS 3RT2926-1BF00 is a varistor-type surge suppressor designed to clip onto the coil terminals of S0-frame contactors in the 3RT2.2 series. It suppresses voltage spikes from the inductive coil when the contactor drops out — protecting nearby PLC outputs, sensors, and control-circuit wiring from back-EMF that can exceed 1 kV on a 400 V AC line. The varistor clamps the transient rather than shunting it through a diode or RC network, which means it handles bidirectional spikes without polarity concerns — a clean fit for AC coils.
This suppressor clips directly onto the contactor — no DIN-rail footprint, no wiring beyond the two coil terminals. The dimensions are 12 mm deep, 30 mm wide, and 19 mm high, so it adds negligible bulk to the S0 contactor stack. Mounting position is unrestricted, which helps when the contactor is oriented sideways or upside-down in a dense panel. Because it's a clip-on accessory for the S0 frame, it does not change the contactor's side-by-side mounting clearance or the required 6 mm gap to grounded parts. If the panel was laid out for a 3RT1023 or similar S0 contactor, this suppressor fits without reworking the gland plate or terminal rail.
For a BOM freeze or compliance audit, this is the documentation-ready date to reference.