What it is and what it does
The Schneider Electric A9F08120 is a single-pole Acti9 iC60H miniature circuit breaker rated at 20 A with a D tripping curve. It is a thermal-magnetic MCB designed for distribution applications, mounted on a DIN rail in a standard 18 mm width (2 x 9 mm pitches). The D curve means the magnetic trip operates at 12 x In (±20 %), so it tolerates the high inrush currents typical of motor, transformer, or lighting ballast loads without nuisance tripping. This makes it a fit for circuits feeding inductive or capacitive loads where a B or C curve would trip on startup. Breaking capacity is 42 kA Icu at 12-60 V AC (50/60 Hz) per EN/IEC 60947-2, and 10 kA Icn at 230 V AC per EN/IEC 60898-1. The part is certified to both standards, so it can be specified for industrial panel protection (60947-2) or residential/commercial final circuits (60898-1).
Where it goes and how it connects
Snaps onto a DIN rail, 18 mm wide — one module width in a standard distribution board or industrial enclosure. Double terminals top and bottom accept 1-25 mm² rigid or 1-16 mm² flexible wire; torque to 2 N·m. Wire strip length is 14 mm. IP20 finger-safe protection (suitable for enclosed panels only). Pollution degree 3 and overvoltage category IV mean it is rated for the harsh electrical environment typical of industrial main distribution panels. Rated insulation voltage 500 V AC, so it can be used in 400 V three-phase systems with confidence. The toggle switch includes a trip indicator and a contact position indicator for visual fault isolation.