Coupling relay for switching auxiliary circuits
The Siemens 3RH2122-1SB40 is a SIRIUS coupling relay — size S00 frame — designed to switch auxiliary circuits in control panels. It carries 2 instantaneous NO contacts rated 10 A at both 24 V and 230 V, making it suitable for interposing between a PLC output and a higher-current load or for signal duplication in safety circuits. The coil is 24 V DC with a built-in suppressor diode, drawing 1.6 W closing power. The pickup/dropout voltage range is 0.85 to 1.85 of rated value — meaning it picks up reliably at 20.4 V and holds in up to 44.4 V, giving headroom on a 24 V bus with ripple.
Panel fit and clearance
These are minimum air gaps to adjacent metalwork or other devices — factor them into the panel layout to avoid arc flash or tracking at pollution degree 3 (conductive or dry non-conductive pollution typical of industrial environments).
Switching ratings and endurance
This is typical for DC switching where arc extinction is harder at higher voltages. Mechanical endurance is 30 million cycles typical — the contacts outlast most panel lifetimes. The arcing time itself is 10 to 15 ms, consistent with the DC suppression diode.
Minimum relative humidity is 10% — no upper bound specified, but the pollution degree 3 rating implies it tolerates conductive dust and occasional condensation. The substance prohibitance date of 10/01/2009 aligns with RoHS compliance for the European market. No auxiliary switch extension is available on this variant (product extension auxiliary switch: No), so the contact configuration is fixed at 2 NO.