The Siemens SIRIUS 3RV1991-1CA0 is an auxiliary switch designed to snap onto 3RV1 motor-protective circuit breakers in sizes 5, 6, 7, and 8. It gives you 3 signaling changeover contacts and 1 dedicated tripped-signal contact, all at 24 V DC coil voltage. That tripped-signal contact is the one you wire to your PLC or indicator lamp to show the breaker has opened on overload or short circuit — it's the difference between knowing a motor stopped because it was told to, and knowing it stopped because the protection fired.
Mounting and fit
This auxiliary switch clips directly onto the front of the 3RV1 breaker — no tools, no wiring to the main poles. If you're swapping a failed switch on a running line, you can do it without pulling the breaker out of the panel. The 3 signaling changeover contacts handle the normal status feedback (ON/OFF/TRIPPED), and the separate tripped-signal contact gives you a dedicated path that only closes when the breaker actually tripped. That saves you from having to decode the status from a single changeover contact.