What the ratings mean for your panel
The Siemens 5SL4320-7CC is a SENTRON miniature circuit breaker rated 20 A at 400 V AC with a C tripping characteristic and a 10 kA breaking capacity per EN 60898. The C-curve means it trips between 5 and 10 times rated current — the standard choice for general-purpose loads like lighting, socket outlets, and small motor circuits where moderate inrush is expected. The 10 kA SCCR at 400 V AC tells you this breaker can safely interrupt a fault current up to that level without welding its contacts or cascading failure upstream, assuming the panel's prospective short-circuit current stays within that limit. Three-pole design (3P) switches all phases simultaneously, so it is suited for three-phase branch circuits in residential, commercial, and infrastructure distribution boards.
Panel integration and mounting
The breaker occupies 3 modular width units (each 18 mm) on a standard DIN rail, with a depth of 76 mm and height of 90 mm. It mounts in any position and requires 70 mm installation depth behind the panel surface. Touch protection is built in, and the housing is halogen-free and silicon-free — relevant for clean-room or low-smoke environments. IP20 with connected conductors means it is protected against finger contact but not washdown; this is a dry indoor panel part.
Thermal derating and ambient range
Rated current is 20 A at 30 °C ambient. At elevated panel temperatures the breaker derates: 18.94 A at 40 °C, 18.39 A at 45 °C, 17.82 A at 50 °C, and 17.24 A at 55 °C. If your panel runs hot — say, a packed enclosure near a furnace line — size your load to the derated figure at the actual ambient, not the 20 A nameplate. The operating ambient range spans -40 °C to 75 °C, so it handles cold starts in unheated substations.