What it is and what it does
The Siemens 5SU9326-1CR20 is a 2-pole RCD-operated circuit breaker (RCBO) from the SENTRON series, combining overcurrent protection and residual current protection in a single 4-module-width unit. It is rated 20 A with a 30 mA residual current trip threshold and a Type C tripping characteristic, meaning it handles moderate inrush from motor or lighting loads without nuisance tripping. The 6 kA breaking capacity per EN 60898 and IEC 60947-2 covers most commercial and light industrial panel fault levels.
Ratings and derating — what matters for fit
The 20 A rating is at 30 °C ambient. At 40 °C it derates to 18.6 A, at 45 °C to 17.6 A, at 50 °C to 17.2 A, and at 55 °C to 16.6 A. If the panel runs warm, size the circuit for the derated figure, not the 20 A label. The insulation voltage is rated 440 V, and the unit is designed for overvoltage category III and pollution degree 2 — standard for fixed-installation distribution boards.
Mounting and integration
Snaps onto DIN rail, occupies 4 modular width units (72 mm wide, 90 mm tall, 77 mm deep, 70 mm installation depth). Mounting position is any orientation. Supply can enter from top or bottom. The IP20 rating applies once installed in a distribution board with conductors connected — not for open-panel or wet-area use. Halogen-free and silicon-free construction suits environments sensitive to outgassing, such as clean rooms or medical facilities.