What the ratings mean for fit
The Siemens 5SU9353-7CR25 is a 1P+N RCBO combining overcurrent and residual current protection in a single module. The 4.5 kA breaking capacity (Icn) at 230 V AC is sized for residential and light commercial distribution boards where the prospective short-circuit current stays under that threshold — typical for TN and TT systems in most European installations. The 30 mA residual sensitivity (Type A) catches sinusoidal AC faults plus pulsating DC faults up to 6 mA smooth DC, covering the majority of modern electronic loads (SMPS, LED drivers, VFDs) that a pure AC-sensitive RCD would miss. The C-curve (C-Char) means the magnetic trip activates at 5 to 10 times In (125–250 A), suited for circuits with moderate inrush — think motorized valves, small pumps, or a bank of fluorescent luminaires. The 25 A rated current (In) matches a 4 mm² copper circuit on a 25 A MCB backup; derate if the ambient in the enclosure exceeds 30 °C.
Deployment context
Snaps onto standard DIN rail in a consumer unit or sub-distribution board. The 1P+N form factor occupies a single module width, so it retrofits into existing board layouts without respacing. Type A residual protection means it is the correct choice for circuits feeding single-phase VFDs, washing machines, or IT equipment — any load that can generate pulsating DC fault currents.