The Siemens 5SY3020-7KL is a SENTRON miniature circuit breaker (MCB) in a compact 1P+N form factor, rated 20 A with a C tripping characteristic and 4.5 kA breaking capacity per EN 60898. That C-curve means it's built for moderate inrush — motor starters, small transformers, lighting banks — where the magnetic trip holds through a short surge but clears a hard fault fast. The single-module width (18 mm) and standard rail mounting let it snap into any DIN-rail enclosure without eating panel real estate.
At 30 °C ambient it carries the full 20 A; derate to 18.8 A at 40 °C and 18.2 A at 45 °C (–). The 4.5 kA breaking capacity at 230 V AC covers most commercial and light industrial fault levels; if your service entrance is higher, step up to the 6 kA or 10 kA SENTRON siblings. Maximum single-phase voltage is 250 V, so it's a straight fit for 230/240 V line-to-neutral circuits.
Panel fit and handling
18 mm wide, 90 mm tall, 76 mm deep — one modular unit on the DIN rail. Mounting position is any, which helps in tight retrofits where the rail is vertical or upside-down.