The Siemens SIRIUS 3RV1991-1BA0 is an auxiliary switch for size 3RV1.5, 6, 7, and 8 circuit breakers. It provides 3 signaling changeover contacts plus a dedicated tripped signal contact, all rated at 250 V AC/DC.
Compared to the 3RV1011-0GA10 motor-protective circuit breaker (which includes its own auxiliary switch and a 0.63 A thermal-magnetic trip), the 3RV1991-1BA0 is purely a signaling add-on — it carries no main contacts, no overload release, and no short-circuit trip. It clips onto the breaker's side, not replacing it. If your BOM specifies a 3RV1011-0GA10 and you already have the breaker, this auxiliary switch is the correct companion for the signaling contacts.
The auxiliary switch shares the breaker's footprint — no extra DIN rail space needed. Screw terminals accept 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or ferruled stranded wire; torque to 0.8–1.2 N·m.