What this varistor does on a contactor coil
The 3RT5926-1BF00 is a varistor-type surge suppressor from the SIRIUS family, designed to clamp voltage transients across an AC contactor coil. It mounts directly onto the contactor — no separate bracket or wiring harness — so it fits within the same DIN footprint as the contactor itself. Rated for AC control supply voltage: 400–600 V at 50 Hz and 600–400 V at 60 Hz. The 50 Hz range is the one most panel builders will size against; the 60 Hz range flips the order (600–400 V) because the varistor's clamping threshold tracks the peak of the sine wave, which shifts with frequency.