What it is — and what the ratings mean for fit
The Siemens SENTRON 5SU9654-7KK20 is a 2-pole RCD-operated circuit breaker (RCBO) combining overcurrent protection and residual current detection in one 36 mm wide, 77 mm deep module — 2 modular width units on a DIN rail, mountable in any position, with supply feed from top or bottom. Rated 20 A at 30 °C with a C tripping curve, it handles moderate inrush from motorized or capacitive loads without nuisance trips. The 300 mA residual current rating (Type A) detects sinusoidal AC and pulsating DC fault currents — typical for circuits feeding electronics, variable-speed drives, or lighting where smooth DC components may appear. Breaking capacity is 10 kA per EN 60898, which certifies the device can safely interrupt short-circuit faults up to that level in a 264 V insulation-voltage system. Overvoltage Category III and a 4 kV surge voltage resistance mean it is rated for fixed-installation panels downstream of the main distribution board.
Derating and ambient temperature
The 20 A rating holds at 30 °C ambient. At 40 °C it derates to 18.8 A, at 50 °C to 17.4 A, and at 55 °C to 16.2 A — so in a warm enclosure (common in packed panels) the connected load must be sized accordingly. Operating range spans -40 °C to 75 °C, covering outdoor cabinets in cold climates.
Panel integration notes
Two modular-width units (36 mm) snap onto a DIN rail; the 77 mm depth fits standard enclosures. Installation depth is 70 mm. Degree of pollution 2 and IP20 when installed in a distribution board with connected conductors.