The Siemens SENTRON 5SU1324-7FA25 is a 2-pole RCBO combining overcurrent protection (C-curve, 25 A) with 30 mA residual-current protection (type A) in a single 3-module-wide unit. It is rated to clear a fault at 10 kA per EN 60898 and 20 kA per IEC 60947-2, so it handles the higher prospective fault current you'd see on an industrial distribution board, not just a domestic sub-main. The 77 mm depth and 54 mm width mean it occupies three 18 mm modular spaces on the DIN rail — standard for a 2-pole RCBO in this class.
Ratings and what they mean on the line
The C-curve trips between 5 and 10 times rated current (125–250 A for this 25 A unit), which is the standard choice for inductive loads like contactor coils, small motors, and control transformers — the kind of inrush that would nuisance-trip a B-curve. The 30 mA type A residual element catches pulsating DC fault currents from single-phase rectifiers or electronic loads, not just sinusoidal AC. On a mill panel that means it covers VFD input rectifiers and switched-mode supplies without needing a separate type B device. Dual breaking capacity: 10 kA per EN 60898 (the household-standard test) and 20 kA per IEC 60947-2 (the industrial standard). The 20 kA rating is the one that matters for a distribution board fed by a transformer with low impedance — it confirms the device can interrupt a fault up to that level without welding its contacts or bursting its arc chamber. The 4 kV surge voltage resistance and overvoltage category III mean it's rated for fixed-installation use downstream of the main incoming supply, not just final circuits. Rated insulation voltage 264 V on a 230/240 V nominal system gives headroom for steady-state voltage variations without degrading the internal clearance. Operating frequency is 50 Hz — verify before deploying on a 60 Hz system; the magnetic core and trip thresholds are tuned for 50 Hz zero-crossing behaviour.
Mounting and environment
Mounts on a 35 mm DIN rail in any position. The 70 mm installation depth is the space needed behind the panel door — factor that into gland-plate clearance if the enclosure is shallow. IP20 only when installed in a distribution board with conductors connected; not rated for washdown or outdoor exposure without an IP54+ enclosure over it. Ambient range -40 °C to 75 °C covers unheated warehouses and hot panel interiors near drives. Halogen-free and silicon-free construction matters if the panel is in a zone where corrosive off-gassing from a fire could damage nearby electronics, or where silicone outgassing would contaminate contact surfaces. Mechanical service life is 10 000 operating cycles — adequate for a distribution board that sees infrequent switching (manual isolation, test trips). Not rated for continuous switching duty like a contactor.