The Siemens 5SY4640-7CV is a 3P+N miniature circuit breaker rated for 40 A with a C-trip curve, breaking up to 15 kA at 400 V. The C-curve (5–10× In) is the standard choice for general-purpose distribution circuits feeding motor starters, contactor coils, and small transformers where moderate inrush is expected — it rides out the magnetizing surge without nuisance tripping on a pump or compressor start.
What the ratings mean for fit
The 15 kA Icu at 400 V is the ultimate short-circuit breaking capacity — the breaker can safely interrupt a fault current up to that level once and still be functional afterward. In a 400 V three-phase panel with a transformer rating that can deliver fault current in that range, this MCB provides adequate protection without needing an upstream current-limiting fuse. The 3P+N configuration switches all three phases and switches the neutral, which is required in some regional wiring codes (e.g., UK, Australia) where the neutral is not considered a solidly-grounded conductor.
Panel integration
Snap-on mounting to a standard 35 mm DIN rail. The 3P+N width occupies four modular spaces (4 x 18 mm). Busbar comb connections are compatible with the Siemens 5SY busbar system for distributing the incoming supply across multiple MCBs in a sub-distribution board.