The Schneider Electric A9F57240 is an Acti9 IKQ miniature circuit breaker rated 40 A with a C-curve trip characteristic (magnetic trip between 5 and 10 times In). The 2-pole configuration protects both phase and neutral on a single-phase AC supply or one phase of a three-phase system. For loads with higher inrush (welding equipment, large transformers), a D-curve would be needed to avoid nuisance tripping. The thermal-magnetic trip unit handles overloads via the thermal bimetal and short-circuits via the solenoid, so no auxiliary power is required for trip operation.
Installation and panel integration
Snap-on DIN rail mounting (35 mm) with plug-on terminals. Bottom terminals accept 1–35 mm² rigid or 1–25 mm² flexible conductors; strip length 14 mm, tighten to 3.5 N·m. Padlockable toggle allows lockout/tagout during maintenance. The trip indicator gives local visual confirmation of the tripped state without needing to check downstream loads.
Standards compliance and documentation
Limitation class 3 per that standard means it limits let-through energy effectively for downstream equipment protection. Service breaking capacity (Ics) is 7500 A at 240 V AC — the level the breaker can repeatedly interrupt without replacement after a fault. Electrical durability rated at 10,000 cycles, mechanical at 20,000 cycles, which covers decades of normal switching in a distribution board.