What it is and what it does
The Siemens 5SU1324-7FN20 is a 2-pole RCBO (residual current circuit breaker with overcurrent protection) from the SENTRON family, combining a 20 A overcurrent trip (characteristic C) with a 30 mA residual current device, type A. It occupies 2 modular width units (36 mm) on a DIN rail and is rated for a breaking capacity of 10 kA per EN 60898. The type A residual current detection means it catches pulsating DC fault currents on top of sinusoidal AC — relevant for modern loads with rectified front ends (VFDs, switched-mode supplies, LED drivers). The C-curve handles moderate inrush from motor starters and contactor coils without nuisance tripping.
Ratings and what they mean for fit
Rated 20 A at 30 °C, derating to 19.5 A at 40 °C and 18.4 A at 60 °C — the thermal curve matters if the RCBO sits in a warm enclosure or next to other heat sources. The 30 mA residual trip threshold is standard for personnel protection (shock risk) per IEC 60364. Insulation voltage is 500 V, surge voltage resistance is 4 kV, overvoltage category III — suitable for fixed-installation distribution boards. The 10 kA breaking capacity at 50 Hz covers most commercial and light industrial service-entrance fault levels; verify against the available fault current at the panel.
Mounting and integration
Snap-on DIN rail mount, 2 MW wide (36 mm). Depth is 72 mm, installation depth 70 mm — check gland-plate clearance if the panel has a shallow back wall. Mounting position is any; supply can enter from top or bottom. IP20 with connected conductors in an installed distribution board — not for wet or dusty environments without an enclosure. Halogen-free? No — standard thermoplastic housing.
Lifecycle and sourcing
Current production — no phase-out or last-time-buy notice on record. This is a standard SENTRON catalog item, broadly stocked across distribution.