What this MCB is and where it fits
The Siemens 5SJ4313-7HG42 is a SENTRON 5SJ4 miniature circuit breaker (MCB) with three poles, a C-curve tripping characteristic, and a 13 A rated current. It snaps onto a standard mounting rail (DIN rail) inside a distribution board or control panel, occupying three modular width units (54 mm total). The C-curve means the magnetic trip operates at 5 to 10 times rated current, which suits mixed resistive and moderate inductive loads common in mechanical engineering and industrial panel builds.
Thermal derating — the real current capability
Rated current holds at 13 A up to 40 °C ambient. Above that, it derates: 12.6 A at 45 °C, 12.2 A at 50 °C, 11.8 A at 55 °C, and 11.4 A at 60 °C. If this breaker sits in a warm enclosure — near transformers, drives, or a furnace control cabinet — size the load against the derated figure, not the 13 A label. Pollution degree 3 and overvoltage category 3 mean it's rated for industrial environments where conductive dust or condensation is expected.