The Siemens 5SL6650-6BB is a miniature circuit breaker (MCB) rated for 400 V with a 6 kA breaking capacity, configured as 3+N-pole with a B tripping characteristic and a 50 A current rating. This is the Italian-market version of the unit.
The B-curve characteristic means the breaker trips at 3 to 5 times rated current (150–250 A), which suits resistive and general-purpose loads where inrush is modest — think lighting circuits, small heaters, or control transformers. The 6 kA breaking capacity at 400 V tells you it can safely interrupt a fault current up to 6,000 A without welding its contacts or cascading failure upstream.