Siemens 5SU1344-7KK82 is a SENTRON RCBO — a combined residual-current circuit breaker with overcurrent protection — rated 125 A at 30 °C, 4-pole (4P), type A residual current, C characteristic, with a 10 kA breaking capacity per EN 60898 and IEC 60947-2.
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 this RCBO lives in a crowded panel where internal temperature hits 50 °C, you have 106.25 A of usable capacity — not 125 A. Plan the load accordingly or allow ventilation. The 30 mA type A residual detects pulsating DC fault currents (typical from rectified loads like switching power supplies, LED drivers, or VFDs) as well as sinusoidal AC. Type A is the minimum for circuits feeding electronics; if your load is pure resistive (heaters, incandescent lighting), a type AC would also work, but type A covers more ground without over-specifying. That suits moderate inrush loads — lighting banks, small motor circuits, distribution subfeeds. For high-inrush transformers or large motors, a D curve would be needed; for purely resistive circuits, a B curve would be faster. C is the middle ground, common in general-purpose final subcircuits. If the prospective short-circuit current (PSCC) at the installation point exceeds 10 kA, you need upstream current-limiting or a higher-rated device. This is a standard residential/commercial value; heavy industrial switchboards often require 16–25 kA.
The 5SU1344-7KK82 occupies 11 modular width units (198 mm wide) on a DIN rail, with a depth of 77 mm and installation depth of 70 mm. It mounts in any position — vertical, horizontal, or flat — which helps in tight enclosures.