What this MCB carries — and what it doesn't
The Siemens 5SY3020-7KV26 is a 1+N-pole miniature circuit breaker rated C20A at 230 V AC with a 4.5 kA breaking capacity. The neutral pole is on the left side of the assembly, and the overall depth is 70 mm — that dimension governs how it sits in a shallow enclosure or against a backplate. The '1+N' topology means the neutral is switched but not protected; only the line pole has the thermal-magnetic trip. For a 20 A C-curve MCB this is a standard choice for general-purpose branch circuits where neutral protection is not required by local code.
The 70 mm depth fits most distribution boards, but check the enclosure's internal depth if you're retrofitting into a shallow consumer unit — some budget enclosures run 68 mm internal and this will overhang. Neutral on left means the busbar or feed-in arrangement must respect the pole order; a standard 1+N busbar with neutral on the left side mates directly.