The A9N26597: This block snaps onto the load side of a compatible Schneider MCB or switch to create a combined RCBO or RCCB assembly. The 4-pole configuration covers three-phase plus neutral. The 300mA sensitivity is a standard for general-purpose earth leakage protection — it's not intended for personal shock protection (that's 30mA), but for fire prevention and equipment protection where higher earth leakage is tolerable. In a panel, it occupies the same DIN-rail footprint as the host device, so no extra width is needed.
The 25A rating means this block is sized for circuits up to that current — typically lighting, small power, or control circuits in commercial or light industrial distribution boards. It's an add-on block, not a standalone device, so it must be mechanically and electrically coupled to a compatible Schneider MCB or switch. The 300mA AC sensitivity is for sinusoidal AC residual currents only; it won't respond to pulsating DC or smooth DC faults.