The Siemens 5SL6640-6BB is a miniature circuit breaker (MCB) rated 400 V with a 6 kA breaking capacity, 3+N-pole configuration, B-curve trip characteristic, and 40 A current rating — the Italy-version variant. The B-curve means it trips between 3 and 5 times rated current, which suits resistive and general-purpose loads where you want to avoid nuisance trips from moderate inrush. The 6 kA interrupting rating at 400 V is enough for most commercial and light industrial distribution boards; it safely clears a fault up to that level without the arc re-striking inside the enclosure.
Panel fit and deployment
Snaps onto standard DIN rail in the distribution board. The 3+N-pole format (three protected phases plus a switched neutral) is common in Italian and other European-installation practice where the neutral is switched alongside the phases. The 40 A rating and 6 kA breaking capacity fit final sub-circuits feeding lighting, socket outlets, or small HVAC loads in a 400 V three-phase system. The B-curve keeps it from dropping out on transformer inrush or motor starting currents that stay under 5x rated — a good match for resistive or lightly inductive loads.