What this MCB is and what it does
The Siemens 5SL3220-7 is a 2-pole miniature circuit breaker from the SENTRON family, rated 20 A at 400 V AC with a C tripping characteristic. Per the datasheet, it breaks 4.5 kA under EN 60898 and 5 kA under IEC 60947-2 — the higher figure applies when the breaker is applied in an industrial distribution context where the standard allows it. The C-curve means it trips between 5 and 10 times rated current, so it handles moderate inrush from small motor or lighting loads without nuisance tripping, while still clearing a hard short within the rated interrupting capacity.
Thermal derating and real-world current
The 20 A rating holds at 30 °C ambient. At 40 °C the continuous current drops to 18.79 A; at 45 °C it's 18.6 A; at 55 °C it's 16.8 A. If the panel ambient runs above 30 °C — common in a crowded enclosure — the load current must be derated per these figures or the breaker will nuisance-trip on thermal overload. The mechanical service life is 10 000 switching cycles typical, which is adequate for a distribution board that sees infrequent manual operation.
Mounting and integration
The 5SL3220-7 occupies 2 modular width units (36 mm total) on a DIN rail. Installation depth is 70 mm; the overall depth including the front toggle is 76 mm. It mounts in any position and is rated IP20 with connected conductors — standard for a panelboard MCB, not for wet locations. Pollution degree 2 and overvoltage category III suit it for fixed-installation distribution boards in residential or light commercial infrastructure.