What this RCBO is and what it does
The Siemens SENTRON 5SU1324-7KK82 is a 2-pole residual current circuit breaker with overcurrent protection (RCBO) rated at 125 A with a 30 mA Type A residual current trip and C-curve tripping characteristic. It breaks fault currents up to 10 kA per EN 60898 and IEC 60947-2, so it handles both the overcurrent and ground-fault protection in a single 7-module-wide unit on the DIN rail.
Ratings and what they mean for your panel
The 125 A rating at 30 °C is the headline number, but the real working current depends on your enclosure ambient. At 40 °C it derates to 115.62 A, at 45 °C to 111.25 A, at 50 °C to 106.25 A, at 55 °C to 101.25 A, and at 60 °C to 96.25 A. If your panel runs hot — say 50 °C inside a sealed cabinet — you need to size the upstream breaker for 106 A, not 125 A. The 30 mA Type A residual current trip catches sinusoidal AC faults and pulsating DC faults. The C-curve suits motor and lighting loads with moderate inrush. Breaking capacity is 10 kA under both EN 60898 and IEC 60947-2, meaning it can safely interrupt a 10 kA prospective fault current at the installation point. The insulation voltage is rated 264 V, and overvoltage category III applies — suitable for fixed-installation distribution boards downstream of the main panel.
Mounting and integration
Snaps onto a 35 mm DIN rail in any mounting position. It occupies 7 modular width units (roughly 123 mm on the rail). Depth is 77 mm, width 117 mm, height 90 mm, with an installation depth of 70 mm behind the panel face. Supply can enter from top or bottom — no orientation restriction. The IP20 rating applies once installed in a distribution board with connected conductors; the housing itself provides touch protection. Halogen-free and silicon-free construction matters if this goes into a clean environment or a panel where outgassing could affect contacts or optics. Pollution degree 2 (non-conductive pollution with occasional condensation) is the standard for most commercial and light-industrial distribution boards.