The Siemens 5SU9304-7KX20 is a SENTRON RCBO — an RCD-operated circuit breaker combining overcurrent protection and residual current detection in a single 18 mm wide module. It's rated 20 A at 30 °C with a C tripping characteristic, Type A fault current sensitivity, and a 10 kA breaking capacity certified to both EN 60898 and IEC 60947-2. That dual certification means it's accepted across residential, commercial, and light industrial panel builds where the local standard may reference either norm. Type A detection handles pulsating DC residual currents up to 6 mA superimposed on AC — common from rectified loads like LED drivers, switched-mode power supplies, and variable-speed drives. If your panel feeds any electronics, Type A is the correct choice over Type AC.
Above that, the continuous current must be derated: 19 A at 40 °C, 18.2 A at 45 °C, 17.6 A at 50 °C, and 17.2 A at 55 °C. If the panel interior runs hot — and most enclosed panels do — size the load circuit for the derated value at your expected ambient, not the headline 20 A.
The 18 mm width (1 width unit) fits standard DIN-rail enclosures. Mounting position is any orientation, so it works in vertical or horizontal busbar arrangements without derating.
Rated for overvoltage category III, protection class IP20 (IP40 with connected conductors in a distribution board), halogen-free and silicon-free construction. Touch protection is included on the terminals.