What this MCB covers
The Schneider Electric A9P42720 is an Acti9 iC40 miniature circuit breaker rated 20 A, 3P+N, with a B tripping curve. The B curve trips magnetically at 3 to 5 times In (3...5 x In per EN/IEC 60898-1, 4 x In +/- 20 % per EN/IEC 60947-2), so it clears a short-circuit fast enough to avoid nuisance trips on moderate inrush, yet it still holds on normal starting current of a resistive load. Breaking capacity is 4.5 kA Icn at 400 V AC (EN/IEC 60898-1) and 6 kA Icu at 400 V AC (EN/IEC 60947-2). That dual rating means it qualifies for both domestic-standard (60898) and industrial-standard (60947) installations — the higher Icu figure is the ultimate breaking capacity under the industrial standard, which is what a panel designer checks for fault-withstand coordination upstream.
Height 85 mm, depth 74 mm. Terminal tunnels accept 1…16 mm² rigid or 1…10 mm² flexible, stripped 14 mm, torqued to 2 N·m. Neutral is on the left (fixed position). IP20 on the body, IP40 inside a modular enclosure — fine for a clean distribution board, not for washdown zones.