The Schneider Electric A9N21407 is a ProDis DT40N miniature circuit breaker rated 20 A with a C-curve trip characteristic (magnetic tripping between 5 and 10 times In). The 3P+N configuration protects three phases and switches the neutral; the neutral pole is unmonitored (no overcurrent protection on N), which is the typical European distribution panel layout. Breaking capacity is dual-rated: 6 kA Icn at 400 V AC per EN/IEC 60898-1 for standard household/commercial duty, and 10 kA Icu at 400–415 V AC per EN/IEC 60947-2 for industrial panel applications. The thermal-magnetic trip unit combines a bimetal strip for overload protection (time-delayed, inversely proportional to current) and a solenoid for short-circuit protection (instantaneous above the magnetic threshold). This is the workhorse trip technology for 95% of distribution MCBs — no electronic adjustment, no auxiliary power needed, just reliable passive operation across the rated temperature range.
The 54 mm width (6 x 9 mm pitches) is the standard 3P+N footprint — it occupies the same slot width as any other 3P+N MCB in the ProDis range, so swapping in a replacement or adding downstream devices doesn't require re-spacing the rail. Tunnel-type terminals accept 0.33–10 mm² flexible or 0.75–16 mm² rigid conductors upstream and downstream. The terminal range covers everything from 1.5 mm² lighting circuits up to 16 mm² main feeders — no need for pin ferrules on the flexible side, though ferrules make insertion cleaner on multi-strand.
Dual-standard compliance (EN/IEC 60898-1 and EN/IEC 60947-2) means it carries both the 'H' (household) and 'I' (industrial) certifications — one part number covers both the commercial building spec and the industrial panel spec.