This is the part that sits in a distribution board protecting a final sub-circuit — lighting, general-purpose sockets, or small motor loads — where the B-curve's magnetic trip between 3 and 5 times In clears short-circuits fast enough to avoid nuisance trips from inrush.
Snap-on mounting to DIN rail EN 60715 — standard 35 mm profile. The 1-pole width (roughly 18 mm per pole) means this unit occupies one module position in a consumer unit or sub-distribution board.
