The Siemens 5SU1654-1KV40 is a combined residual-current device and miniature circuit breaker (RCBO) — an FI/LS protector — in a single 1+N-pole module. It integrates Type AC residual current detection at 300 mA with a C-curve overcurrent trip at 40 A, all within a 70 mm deep enclosure. The 10 kA breaking capacity means it can safely interrupt fault currents up to that level at the rated voltage, which is the standard requirement for most residential and light commercial distribution boards. The C-curve characteristic suits loads with moderate inrush, such as small motor circuits, lighting banks, and general socket outlets.
What the ratings mean for fit
The 300 mA residual sensitivity (IΔn) is the trip threshold for earth leakage — Type AC means it detects sinusoidal AC fault currents only, not pulsating DC or smooth DC. This is the standard choice for general-purpose circuits where no electronic loads or variable-speed drives are downstream. The C 40 A overcurrent element provides magnetic trip between 5× and 10× rated current (200–400 A), covering motor starting and capacitive loads without nuisance tripping. The 10 kA breaking capacity (Icn) matches the typical prospective short-circuit current at the service entrance of a residential or small commercial panel; verify the available fault current at the point of installation does not exceed this.
Panel integration
The 1+N-pole format occupies a single modular width on the DIN rail, with the switched phase on the left and a switched neutral on the right. The 70 mm depth fits standard distribution board enclosures without crowding the gland plate. Wire the supply to the top terminals and the load to the bottom; the neutral busbar connects through the device, so no separate neutral link is needed downstream.