The Siemens 3RH1921-1DA11-ZX90 is a first lateral auxiliary switch from the SIRIUS family, designed to snap onto 3RT1 contactors. It carries one normally-open and one normally-closed contact, wired via screw terminals, and is rated for 10 A at 24 V. With a mechanical service life of 10 million switching cycles, it's built for high-throughput panel applications where the main contactor's auxiliary contacts are already consumed or you need additional isolated feedback.
Snap-on mounting means this block clips directly onto the front of a 3RT1 contactor without tools — no extra DIN rail space, no brackets. The 10 mm width matches the contactor's profile, so it doesn't widen the footprint. Screw terminals accept 2x (0.5...1.5 mm²) or 2x (0.75...2.5 mm²) with core-end processing, or 2x (20...16) and 2x (18...14) AWG. Strip length is standard; a 6 kV surge voltage resistance covers most industrial environments.
Current ratings are given per the contact duty: 10 A at 24 V, 6 A at 125 V, 6 A at 230 V, 3 A at 400 V. The DC curve drops faster — 6 A at 24 V, 2 A at 60 V, 1 A at 110 V, 0.3 A at 220 V. That's typical for a general-purpose auxiliary switch; if you're switching a DC solenoid at 110 V, the 1 A limit is the one that governs. Contact reliability is rated at 1 faulty switching per 100 million operations at 17 V, 1 mA — fine for PLC-level signals.