20 A, 1-pole, C-curve — what the ratings mean for your panel
The Siemens 5SL1120-7MB is a SENTRON miniature circuit breaker rated 20 A, single-pole, with a C tripping characteristic. That C-curve means it trips at 5 to 10 times rated current — designed for moderate inrush loads like small motors, lighting banks, and control transformers where a B-curve would nuisance-trip. The 3 kA breaking capacity per IEC 60947-2 tells you it can safely interrupt a fault up to 3 kA at 230/400 V AC without welding contacts or cascading upstream. For residential and light commercial distribution boards this is the standard interrupting rating; if your fault current exceeds 3 kA, step up to the 6 kA or 10 kA variants in the same family.
DIN-rail footprint and panel fit
Occupies 1 modular width unit (18 mm) on a standard DIN rail — installs in any position. Depth is 76 mm, height 90 mm, installation depth 70 mm. The IP20 rating (with connected conductors) is typical for enclosed distribution boards; no special sealing needed. Sealable design allows locking the toggle in the OFF position for lockout/tagout. Halogen-free and silicon-free construction matters if the panel is in a clean room or oxygen-enriched environment.