What it is and what it does
The Siemens 3RT1916-2FK21 is a SIRIUS auxiliary switch — a clip-on accessory that adds a timed contact block to a contactor or motor starter. Rated 3 A maximum, it carries a 1 A switching capacity at 24 V and 0.1 A at 250 V. The adjustable time range of 0.5 to 10 s covers common delay-on applications like staggered motor starts or sequence interlocks.
Key ratings and what they mean for fit
The 3 A maximum rating governs the auxiliary contact's thermal continuous current — it's sized for signal-level switching (PLC inputs, relay coils), not motor power. The 0.1 A at 250 V AC rating reflects the break capacity under inductive load; expect derating for DC circuits. The adjustable time range of 0.5 to 10 s is set via a potentiometer on the face, with a recovery time of 150 ms between cycles — enough for most conveyor or pump sequencing, but too slow for fast-cycling applications like stamping presses where a minimum ON period of 200 ms applies. The clip-on fastening method means it snaps directly onto the front of a SIRIUS 3RT2 contactor or 3RA2 starter without tools. Width is 45 mm, depth 75 mm, height 38 mm — it adds one module width to the assembly. Mounting position is any, so it fits horizontal or vertical DIN-rail layouts without derating.
Environmental and insulation specs
Basic insulation with pollution degree 3 means it's suitable for industrial environments where conductive dust or condensation may be present — typical for unsealed control panels. Operating temperature range is -25 to +60 °C; storage and transport range extends to -40 to +85 °C. The 0 m altitude rating for all axes (upwards, forwards, backwards, downwards, at the side) indicates the part is rated for standard atmospheric pressure only — no high-altitude derating is published.