RCBO for final-circuit protection
The Siemens 5SU9336-7CR25 is a 1P+N RCBO combining overcurrent and residual-current protection in a single module. Rated Icn 6 kA at 230 V AC, it clears line-to-neutral faults up to that prospective short-circuit current without upstream fuse coordination — sized for domestic and light commercial distribution boards where the supply-side fault level is known and bounded. The 30 mA Type A RCD catches sinusoidal AC and pulsating DC fault currents, which covers most electronic loads (switched-mode PSUs, variable-speed drives) that a pure AC-sensitive device would miss.
C-curve and 25 A rating — what drives the selection
C-characteristic means the magnetic trip fires at 5–10× In (125–250 A), so it holds motor inrush and capacitive load surges without nuisance tripping, yet still clears hard faults fast. The 25 A thermal rating matches a 4 mm² copper final subcircuit in IEC 60364 installations — typical for socket-outlet rings, fixed appliances up to 5.7 kW (230 V), or lighting banks with high inrush. Pair it with a 25 A rated cable and verify the loop impedance stays below the 0.38 Ω needed for the 6 kA Icn to be effective.
Panel integration — DIN-rail fit and spacing
Snap-on mounting to 35 mm DIN rail per EN 60715. The 1P+N module occupies a single 18 mm width — standard for SENTRON 5SU9 RCBOs. In a multi-pole distribution board, allow one module width per RCBO plus any busbar end-feed gland space. No forced-air cooling required; ambient derating starts above 40 °C per the IEC 60898-1 thermal curve.