What it is and what it does
The Siemens 3RT1916-2GD51 is a SIRIUS-brand auxiliary switch with an adjustable ON-delay timer, designed to clip onto a contactor or star-delta starter assembly. It gives you a timed auxiliary contact that closes after a set delay from coil energization — the adjustable time range spans 1.5 to 30 seconds, with a recovery time of 150 ms before it can be re-triggered. The coil is rated for 200-240 V AC at both 50 and 60 Hz, so it drops straight into a standard European control-voltage circuit without a separate transformer tap. The switching contacts handle 1 A at 24 V, 0.2 A at 125 V, and 0.1 A at 250 V — enough for PLC inputs, pilot lights, or signal relays, not for direct motor switching. The part is explicitly designated for star-delta circuits, meaning the timer is wired into the transition leg between star and delta contactors. If your panel uses a star-delta start scheme, this auxiliary switch is the timed element that holds the star contactor closed for the acceleration period then releases it.
Mounting and integration
Clip-on mounting means it snaps directly onto the front of a SIRIUS contactor or onto a DIN rail adapter — no screws, no tools beyond a screwdriver for the wiring terminals. The body measures 45 mm wide, 38 mm high, and 75 mm deep, and it can be mounted in any position. Terminals accept solid or stranded wire from 18 AWG down to 14 AWG. The IP20 finger-safe enclosure is standard for inside a panel; keep it behind a locked door or within a dead-front enclosure.
Ratings and environment
Basic insulation with pollution degree 3 means it's rated for industrial environments where conductive dust or condensation may occur — standard for an uncoated control-panel device. Storage and transport temperature range is -40 to +85 °C, and operating humidity is 15 to 95 % non-condensing. Maximum operating altitude is 2 000 m. The mechanical endurance is listed as 10 000 000 typical cycles — that's the switch mechanism itself, not the electrical life under load. For the contact ratings given, expect the electrical life to be a fraction of that, especially at the higher voltage/current combinations.