What it is and what the ratings mean
The Siemens 5SL4420-8CC is a 4-pole miniature circuit breaker (MCB) from the Basic Devices family, rated for 400 V AC with a 10 kA breaking capacity and a D-trip curve at 20 A. The D-curve means it tolerates high inrush currents — typically 10 to 20 times the rated current — so it is sized for motor and transformer branch circuits where the start-up surge would nuisance-trip a B or C curve breaker. The 10 kA interrupting rating at 400 V is the standard domestic and light commercial fault level; it safely clears a short-circuit up to that current without welding the contacts or cascading the fault upstream.
Where it fits in the panel
This is a DIN-rail mount MCB — standard 4-pole width (72 mm, 4 module spaces). It snaps onto a 35 mm DIN rail inside a distribution board or sub-panel. The D-curve and 20 A rating make it a direct fit for motor feeder circuits, small compressor or pump branch protection, or any inductive load where the inrush peak is well above the continuous rating.