The Siemens 5SJ6120-7KS is a 1-pole SENTRON miniature circuit breaker from the 5SJ6 series, rated 20 A with a C-curve trip characteristic.
Breaking capacity is 6 kA per both EN 60898 and IEC 60947-2, which covers the majority of residential and light commercial panelboards where the prospective fault current stays under that threshold. The C-curve (5–10× In) handles motor inrush and transformer energization without nuisance tripping, while still clearing low-impedance faults fast enough to limit let-through energy to Class 3.
DC rating and application scope
Rated for DC circuits up to 60 V maximum — covers control-voltage supplies, signal loops, and small DC bus feeds in industrial panels. AC rating is 400 V line-to-line, 230 V phase-to-neutral. The part is designated for residential buildings and infrastructure per the manufacturer's suitability listing; it also fits commercial sub-distribution and light industrial branch circuits where the SCCR requirement does not exceed 6 kA.