It protects a single-phase AC circuit against overload, short-circuit, and earth leakage, with a Type A fault-current sensor that catches pulsating DC residual currents (common from rectifiers, VFDs, and switching supplies) as well as sinusoidal AC faults.
In a domestic or light commercial distribution board with a typical upstream fuse or MCB rated higher, this holds. The C curve means magnetic trip occurs at 5 to 10 times rated current (100–200 A for this 20 A unit), so it's sized for circuits with motor or transformer inrush. Temperature derating is published: 20 A at 30 °C, 19 A at 40 °C, 18 A at 50 °C, 17.4 A at 55 °C. If your enclosure runs hot, size the load accordingly — the 40 °C figure is the one most panels see. The 18 mm width (1 width unit) fits standard SENTRON distribution boards. Touch protection is built in (IP20 with conductors connected).