What this 50 A B-curve MCB means for your panel
The Siemens 5SY6650-6 is a 4-pole (3P+N) SENTRON miniature circuit breaker rated 50 A at 35 °C with a B tripping characteristic — meaning it trips at 3 to 5 times rated current, which makes it a solid choice for resistive and general-purpose loads where you want fast clearing on short circuits but don't need the inrush headroom of a C curve. Out here in the grease, if you're feeding a control transformer or a bank of contactors, the B curve keeps nuisance trips off the floor. At 50 A, this is a main feeder MCB for a sub-panel, not a branch device. It's rated for 50/60 Hz supply and carries an overvoltage category III rating, so it's suited for fixed-installation panels — not plug-in equipment.
Panel fit and environmental tolerance
Installation depth is 70 mm, and the overall depth is 76 mm, so plan for that behind the gland plate. But the temperature range is wide: -40 °C to 75 °C ambient, so it'll handle a hot summer in an unventilated enclosure or a cold storage facility. Degree of pollution 3 means it's designed for conductive pollution environments — think factory floor with some dust and humidity, not a clean room.
Temperature derating and real-world current
The 50 A rating holds at 35 °C. At 45 °C it derates to 47 A; at 50 °C it's 45.95 A; at 55 °C it's 44.9 A. The B curve still trips at 3-5x the derated current. Humidity tolerance is 95% up to 55 °C, dropping to 35% at 75 °C — that's typical for a sealed MCB, but worth noting if your panel sees condensation cycles.