SENTRON 5SJ6520-7FC — 20 A C-curve MCB, 1P+N, 6 kA
The Siemens 5SJ6520-7FC is a SENTRON miniature circuit breaker rated 20 A with a C tripping characteristic, designed for single-phase AC circuits up to 230 V (250 V single-phase). The 1P+N pole design switches both line and neutral, with the neutral pole switching but not protected — a common arrangement for residential and light commercial distribution boards where a single-pole break on the phase is sufficient and the neutral follows for isolation. Breaking capacity is 6 kA per EN 60898, which covers most domestic and light commercial fault levels. The C-curve (5-10x In) handles moderate inrush from small motors, lighting ballasts, and transformers without nuisance tripping while still clearing short circuits fast enough for cable protection.
DIN-rail fit and panel integration
Width is 36 mm (2 modular units), depth 76 mm, height 90 mm. Snaps onto standard 35 mm DIN rail; installation depth is 70 mm behind the panel face. The 2-module width means it occupies two adjacent 18 mm slots — plan your distribution board fill accordingly. Mounting position is any, so vertical or horizontal rail orientation works. IP20 with connected conductors — suitable for enclosed distribution boards only, not for wet or dusty environments. Degree of pollution 2 (normal, non-conductive pollution only). Overvoltage category III, so it's rated for fixed installations downstream of the main panel breaker.
Temperature derating — real-world current capacity
Rated 20 A at 30 °C ambient. At 40 °C it derates to 18.48 A, and at 45 °C to 17.6 A. If your panel ambient runs hot (enclosed board, adjacent heat sources), apply the derated figure rather than the 20 A label — otherwise you risk nuisance tripping on a warm day or, worse, the breaker running above its calibrated thermal curve.