What it is and where it fits
The Siemens 3RH1921-1EA11-ZW97 is a first lateral auxiliary switch block in the SIRIUS family, designed to snap onto the side of SIRIUS 3RT1 contactors and contactor relays. It adds one normally-open and one normally-closed auxiliary contact pair, wired via screw-type terminals, to the base contactor's control circuit. Rated for a maximum of 10 A, with a mechanical service life of 10 million switching cycles typical, this block handles the signal-level and pilot-duty loads common in motor starter and control relay applications. The 10 A rating applies at 24 V; derate for higher voltages per the published curve. Snap-on mounting onto the contactor profile means no additional DIN rail space is consumed — the block adds 10 mm of width to the assembly, keeping the panel layout compact.
Contact ratings and what they mean for the buyer
The auxiliary contacts carry a 10 A continuous rating at 24 V, 6 A at 230 V, and 3 A at 400 V. For DC switching, the block is rated 6 A at 24 V, 2 A at 60 V, and 1 A at 110 V. These are the values that govern whether the block can handle the inrush and sealed current of the downstream PLC input, relay coil, or indicator lamp without welding or excessive temperature rise. Contact reliability is specified at 1 faulty switching per 100 million operations at 17 V, 1 mA — a figure that matters for low-energy signal circuits where oxide films or contamination can prevent closure. The IP20 front protection keeps fingers and tools out during panel access.
Panel integration note
Snap-on mounting onto the 3RT1 contactor profile. The block adds 10 mm width, 71 mm depth, and 80 mm height to the assembly. Screw terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) with core end processing, or 2x (20 to 16) and 2x (18 to 14) AWG. Strip length and torque follow standard Siemens terminal practice for the SIRIUS range.