What it is and what it does
The Siemens 5SU9306-1KK20 is a 1P+N RCBO — a combined overcurrent and residual-current device — from the SENTRON family. It occupies one modular width (18 mm) on a DIN rail, rated 20 A with a 30 mA residual trip and Type C tripping characteristic. The instantaneous design means no intentional delay on fault; it clears fast.
Ratings and what they mean for fit
The 20 A rating at 30 °C derates to 18.8 A at 40 °C, 18.2 A at 45 °C, 17.4 A at 50 °C, and 16.2 A at 55 °C — the thermal curve governs real-world continuous load, not the 30 °C label. The 30 mA residual trip covers AC fault currents (Type AC), standard for general-purpose socket circuits and lighting finals. The Type C curve (5–10× In magnetic trip) suits moderate inrush loads like small motors and fluorescent banks. The 6 kA breaking capacity per EN 60898 is the rated short-circuit capacity at the declared voltage — adequate for most domestic and light commercial distribution boards where the prospective fault current stays under that threshold.
Where it goes and how it mounts
Mounts on a DIN rail in any orientation — the housing is rated for any mounting position. Installation depth is 70 mm; overall depth is 77 mm. Supply can enter from top or bottom. The IP20 rating applies once installed in a distribution board with conductors connected — it is not a standalone outdoor device. Pollution degree 2 (normal, non-conductive) and overvoltage category III (distribution level) are standard for fixed-installation panel gear.