What this RCBO is and where it fits
The Siemens 5SU1324-7FM16 is a 2-pole RCBO (residual current circuit breaker with overcurrent protection) from the SENTRON 5SU1 series, combining a Type A residual current device and a C-characteristic miniature circuit breaker in a single 3-module-wide unit (54 mm). It's rated for 230/240 V AC at 50 Hz, with a 10 kA breaking capacity per EN 60898 — the standard for household and similar installations, certifying its ability to safely interrupt fault currents up to that level. The C tripping curve means it's designed for inductive loads like small motors, pumps, and lighting banks where inrush current can exceed 5× the rated current. Mounts on standard DIN rail in any orientation (mounting position any), with an installation depth of 70 mm and overall depth of 77 mm. Supply can enter from top or bottom — no forced polarity for the line side. Pollution degree 2 and overvoltage category III suit fixed-installation distribution boards in commercial or light industrial panels.
Thermal derating — the real current rating at panel ambient
The headline 16 A rating holds only at 30 °C ambient. In a sealed distribution board running at 40 °C — common in summer or crowded enclosures — the continuous current drops to 15.2 A. At 50 °C it's 14.4 A, and at 60 °C it's 13.6 A. If your panel ambient hits 70 °C, derate to 12.32 A. This is the number that governs real-world loading, not the 30 °C figure. For a pump drawing 14 A continuous at 45 °C, the 14.88 A derated value leaves only 0.88 A headroom — marginal for a circuit that won't nuisance-trip on a hot day.
Type A fault current detection — what it catches
Type A RCD detects sinusoidal AC residual currents plus pulsating DC residual currents — the kind produced by single-phase rectifiers in VFDs, switching power supplies, and LED drivers. If your downstream loads include any electronics that chop the sine wave, Type A is the minimum for code compliance in most IEC regions. The instantaneous design (no intentional time delay) means it trips within the standard RCD response time — no coordination with delayed RCDs upstream.
Halogen-free and silicon-free construction
Both the housing and internal insulation are halogen-free and silicon-free. That matters for installations in environments where outgassing from a fault arc could corrode nearby contacts — think data centers, medical equipment, or clean rooms. Standard RCBOs often use halogenated flame retardants; this one avoids them without sacrificing the IP20 protection rating when mounted in a distribution board with conductors connected.