Siemens 5SL4120-7 SENTRON MCB — 20 A, C-curve, 10 kA
The Siemens 5SL4120-7 is a 1-pole SENTRON miniature circuit breaker with a C-curve trip characteristic, rated 20 A at 30 °C and 400 V AC. Its 10 kA breaking capacity per EN 60898 covers the majority of residential and light commercial fault-current scenarios — enough headroom for most distribution boards fed by a standard utility transformer. The C-curve (5–10× In) is the default for general-purpose loads: lighting, socket outlets, small appliances, and control transformers where inrush isn't extreme. At 40 °C ambient the continuous rating derates to 18.48 A, so a panel running warm needs to account for that gap if the circuit is loaded near the nameplate.
Integration notes
Sealable design (padlockable toggle) and touch protection on the terminals meet the requirements for lockout/tagout procedures and finger-safe wiring per IEC 61439. Halogen-free and silicon-free construction matters for environments where outgassing can contaminate sensitive contacts or optics — clean-room adjacent or sealed enclosures. The 10 000 mechanical switching cycles typical service life is adequate for a distribution breaker that sees infrequent manual operation; it is not rated for frequent switching duty like a contactor.