The Siemens 3RT2936-1JJ00 is a SIRIUS surge suppressor — a varistor with an integrated LED indicator — designed to clamp voltage transients across the coil of a contactor. It mounts directly onto S2- and S3-frame contactors (3RT2.3 and 3RT2.4 families) via a clip-on fastener, occupying no extra DIN-rail space.
It accepts 24–48 V AC at 50/60 Hz and 12–24 V DC, AC/DC control supply. The LED gives a quick visual that the suppressor is live — useful during commissioning or fault-finding without reaching for a meter.
Dimensions are 30 mm wide, 30 mm high, 15 mm deep — a compact block that clips onto the contactor's coil terminals. Mounting position is any orientation. That covers most indoor panel environments without derating.