The Schneider Electric A9F05403 is a 4-pole Acti9 iC60N miniature circuit breaker rated at 3 A with a D tripping curve. It's built to protect branch circuits in distribution panels, mounted on a standard DIN rail. The D curve means the magnetic trip fires at 10 to 20 times rated current — that's 30 to 60 A for this 3 A unit — so it's sized for loads with a high inrush, like small motors, transformers, or solenoid banks, where a B or C curve would nuisance-trip on startup. Rated at 3 A, this is a low-current branch breaker. Let me show you why that matters: on a 4-pole frame, you're protecting all three phases plus neutral on a 3-phase 4-wire system, or using the fourth pole as a switched neutral. The 3 A rating limits it to very light loads — think control transformers under 1 kVA, small pilot circuits, or instrumentation supplies. Don't try to hang a motor starter on this; the inrush alone would hold it in the magnetic region.
Breaking capacity on this breaker is 50 kA Icu at 220-415 V AC per EN/IEC 60947-2, and 10 kA Icn at 400 V per EN/IEC 60898-1. The dual standard (60947-2 for industrial and 60898-1 for residential/commercial) means it's certified for both distribution boards and industrial switchgear. The 10 kA Icn at 400 V is the domestic rating; the 50 kA Icu is the industrial one. If your panel's fault current at the breaker terminals is under 10 kA, either standard covers you. Above that, you rely on the 60947-2 rating. Overvoltage category IV puts it at the service entrance or main distribution board, not downstream sub-panels. The thermal-magnetic trip unit gives you both overload protection (thermal bimetal, slow response) and short-circuit protection (magnetic solenoid, instantaneous at 12 x In ±20%, so 36 A ±7.2 A).
Mounting and wiring — what to expect on the rail
The 4-pole body takes 8 x 9 mm pitches of rail space — that's 72 mm wide. Depth is 78.5 mm, height 91 mm. Strip length is 14 mm. The toggle actuator is manual with a trip-indicator flag that shows a red band when the breaker has tripped — useful for panel troubleshooting without a meter. IP20 finger protection on the front means it's safe for open-panel use as long as no water gets near it. For washdown environments, you'd need an enclosure. The white color is standard for Schneider's Acti9 residential-commercial line — if your panel spec calls for grey or black, flag it now because this one is white.