The Siemens SIRIUS 3RT2916-1LN00-ZX90 is a surge suppressor — a suppression diode with integrated LED — designed for DC control circuits rated 70...150 V. It clips directly onto the coil terminals of S00-size contactors and motor starters, so no additional wiring or DIN-rail space is consumed. The LED gives a quick visual check that the coil circuit is live, which speeds troubleshooting in a crowded panel.
The DC voltage range of 70...150 V matches the control supply on many European and Asian 110/125 VDC systems — verify your coil rating falls inside that window. The diode design means this suppressor is polarity-sensitive: reverse connection defeats the suppression and may damage the diode. For AC coils or bipolar DC circuits, a varistor or RC suppressor would be the correct choice. Physical fit is defined by the S00 footprint: 46 mm high, 28 mm wide, and only 9 mm deep — it adds negligible depth to the contactor stack. The clip-on fastening (no screws, no DIN rail) lets you snap it onto the contactor's coil terminals in seconds, and any mounting position is allowed, which helps when the contactor is mounted on a vertical or horizontal surface. The part carries a RoHS compliance date of 10/01/2009, so it meets the EU substance bans that matter for most BOMs.