What it is and what it does
The Siemens 5SU9326-1CR25 is a SENTRON RCBO — a residual-current-operated circuit breaker that combines overcurrent protection (MCB function) with earth-leakage protection (RCD function) in a single 4-module-wide (72 mm) DIN-rail device. It is rated 25 A at 30 °C with a 30 mA residual trip threshold, type AC (sensitive to sinusoidal AC fault currents), and a C tripping characteristic for moderate inrush loads like motor starters or small transformers. The 6 kA breaking capacity is certified to both EN 60898 and IEC 60947-2, so it handles fault currents up to that level in a 230/400 V distribution board without cascading upstream. Overvoltage category III and pollution degree 2 suit it for fixed-installation panel use.
Temperature derating — the real-world rating
The 25 A rating holds at 30 °C ambient. At 40 °C it derates to 23.3 A, at 45 °C to 22 A, at 50 °C to 21.5 A, and at 55 °C to 20.8 A. If the panel runs warm — common in a crowded enclosure or near a heat source — size the load against the derated figure, not the 30 °C headline.
Panel fit and mounting
Occupies 4 modular width units (72 mm) on a DIN rail, with a depth of 77 mm and an installation depth of 70 mm. The supply can enter from either top or bottom, and the mounting position is unrestricted — no orientation restrictions in the enclosure. Touch protection is built in, and the IP20 rating applies once the distribution board is installed with conductors connected.