What it is and what it does
The Siemens 5SU1336-7FP20 is a 3-pole RCBO (residual current operated circuit-breaker with overcurrent protection) from the SENTRON family, combining an RCD Type A (30 mA sensitivity) and an MCB with C-characteristic (20 A rated current) in one 3-module-wide unit. It protects against earth faults and overload/short-circuit in a single device, saving a DIN rail slot compared to separate units. Rated 400 V AC at 50 Hz, it carries a 6 kA breaking capacity per both EN 60898 and IEC 60947-2 — sufficient for most residential and light commercial distribution boards. The C-curve trips between 5 and 10 times rated current, so it handles motor inrush and transformer energization without nuisance tripping on a 20 A circuit.
Fit and installation
Snaps onto standard 35 mm DIN rail. At 54 mm wide (3 modular width units) and 72 mm deep, it fits a standard 70 mm installation depth enclosure. Supply can enter from top or bottom — no orientation restriction. Mounting position is any, which helps when the board is laid out horizontally. IP20 rated with conductors connected and the distribution board installed — standard for enclosed panel use. Pollution degree 3 and overvoltage category III mean it's rated for fixed installations with transient overvoltages typical of mains supply.
Environmental and mechanical
Rated for -40 °C to +70 °C ambient, with max 95% humidity. Mechanical service life is 10 000 operating cycles typical. Energy limitation class 1 — check normative use limitations for your application, as class 1 allows higher let-through energy than class 3.