What this varistor does on your S0 contactor
The 3RT7926-1BF00 is a varistor-type surge suppressor from the Siemens SIRIUS family, designed to plug directly onto S0-size contactors like the 3RT7 series. Its job is to clamp voltage spikes from the AC control coil when the contactor de-energizes — without it, the inductive kick can arc across the PLC output or relay contacts driving the coil, shortening their life. Rated for AC control supply voltage from 400 V to 600 V at both 50 Hz and 60 Hz, so it covers the common 480 V and 575 V control transformer taps you see in North American and European panels.
Panel fit and mounting — the 12 mm depth matters
This suppressor clips onto the contactor — no extra DIN rail slot needed. The 12 mm depth means it adds almost nothing to the panel depth budget; the 30 mm width and 19 mm height keep it within the S0 contactor footprint. Mounting position is any orientation, which helps when the contactor is installed sideways or upside-down in a dense panel. The clip-on fastening method means no wiring — it snaps onto the contactor coil terminals, so there's no extra point of failure or loose screw to check.
Environmental limits and compliance
Operating temperature range is -10 °C to +55 °C, with storage from -25 °C to +70 °C — fine for most indoor control panels and even unheated warehouses. The substance prohibition date of June 15, 2022 confirms RoHS and REACH compliance for current production.