The Schneider Electric A9N21702 is a Vigi iDPN add-on residual current device from the Clario range, designed as a 3-pole unit rated at 40 A with 300 mA earth-leakage sensitivity.
The 40 A rated current (In) and 400 V AC phase-to-phase operational voltage (Ue) mean this block pairs with a 40 A 3P MCB on a 400 V three-phase system. The 300 mA sensitivity is instantaneous and voltage-independent — it trips on residual current regardless of whether the mains voltage is present, which is useful for circuits where you need ground-fault protection even if the neutral is lost. The 95 % humidity at 55 °C rating backs that up.
Clip-on mounting to DIN rail, 36 mm wide (4 x 9 mm pitches), 81 mm tall, 69 mm deep. The screw terminals accept rigid cable from 0.75 to 16 mm² and flexible from 0.33 to 10 mm². The connection to the MCB is by screws, so it's a mechanical and electrical add-on — not a bus-bar jumper.