What it is and what it does
The Siemens 5SU1344-0KK82 is a SENTRON RCBO — a combined residual-current circuit breaker with overcurrent protection — rated 125 A at 400 V AC, 50 Hz, in a 4-pole (4P) configuration with a B tripping characteristic. The B curve means it trips between 3 and 5 times rated current, suited for resistive and general-purpose loads where inrush is modest. Breaking capacity is 10 kA per both EN 60898 and IEC 60947-2, so it can safely interrupt fault currents up to that level without upstream cascading. Energy limiting class 3 means it restricts let-through energy during a short circuit, reducing stress on downstream components. The fault-current type is AC-sensitive — it detects sinusoidal residual currents. The unit is instantaneous (no intentional time delay), so it responds immediately to ground faults.
Thermal derating and real-world current
The 125 A rating holds at 30 °C 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 the panel runs warm — common in a crowded enclosure — size the load to the derated figure, not the 30 °C headline. Operating temperature range is -40 °C to 75 °C, covering cold storage and hot industrial environments. Pollution degree 2 and overvoltage category III suit fixed-installation distribution boards.
Panel fit and mounting
Width is 198 mm (11 modular width units at 18 mm each), depth 77 mm, height 90 mm, with an installation depth of 70 mm. Mounting position is any orientation. Supply can enter from top or bottom — no mandatory orientation for the line side. Protection class is IP20 when installed in a distribution board with connected conductors — standard for enclosed panel use, not for wet or dusty environments without an outer enclosure. Halogen-free and silicon-free construction matters for installations with strict material restrictions, such as rail or marine applications where outgassing during a fire is a concern.
Lifecycle and sourcing
Compliance documentation includes RoHS and REACH declarations as standard for Siemens SENTRON products. The unit carries ratings per EN 60898 and IEC 60947-2, which are accepted across most European and international jurisdictions.