What this RCBO is and what the ratings mean
The Siemens 5SU1344-8RC40 is a combined residual current circuit breaker with overcurrent protection (RCBO) rated at 40 A, 4-pole, occupying 7 modular DIN spaces. The D characteristic means its magnetic trip curve is designed for loads with high inrush currents — typically motor starters, transformers, or discharge lighting — where a B or C curve would nuisance-trip on startup. The Type A residual current detection (30 mA) handles pulsating DC fault currents from single-phase rectifiers or switched-mode power supplies, which a standard AC-sensitive RCD would miss. This makes it a fit for mixed-load sub-distribution boards where both sinusoidal and pulsed earth faults are possible.
Panel integration and deployment context
The 7-module width (each module being 17.5 mm on a standard DIN rail) means this RCBO occupies about 122.5 mm of rail space — a factor when laying out a crowded sub-distribution board. The 4-pole configuration (3 phases + neutral) suits three-phase final circuits where neutral switching and protection are required. The D-curve magnetic release typically holds up to 10–20× rated current for short durations, so verify the connected load's inrush profile against that window to avoid nuisance tripping on motor start.