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.
What the ratings mean for fit
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. That's standard for most sub-distribution boards in commercial and light industrial panels, but if your available fault current at the panel exceeds 6 kA, you'll need a current-limiting upstream device or a higher-rated MCB.