What it is and what it does
The Siemens SENTRON 5SU1674-7FK81 is a 4-pole RCBO — residual-current circuit breaker with integral overcurrent protection — rated 100 A at 30 °C, with a 300 mA residual trip and Type B+ sensitivity. It occupies 11 modular-width units on a DIN rail. The B+ characteristic means it detects smooth DC residual currents up to 1 kHz, pulsating DC, and AC waveforms — essential for VFD-fed loads, UPS-fed circuits, or PV inverters where standard Type A devices can blind to pure DC faults.
Breaking capacity and coordination
Rated 10 kA per both EN 60898 and IEC 60947-2. That puts it squarely in standard distribution-board fault levels for commercial and light industrial panels. Overvoltage Category III, pollution degree 2 — typical for fixed-installation switchgear in a building main or sub-distribution board. Energy Limitation Class 3 means it limits let-through energy to the lower range, supporting selective coordination with upstream devices.
Thermal derating — the real-world current
The 100 A rating holds at 30 °C ambient. At 40 °C the device is rated 92.5 A; at 50 °C, 85 A; at 60 °C, 77 A. If your panel ambient runs at 45 °C, you have 89 A available. That derating curve matters in a crowded enclosure — the trip unit responds to actual thermal load, not the label. The mounting position is unrestricted, so vertical or horizontal DIN orientation doesn't change the rating.
Halogen-free and silicone-free construction
Marked as halogen-free and silicone-free. For installations with strict low-smoke, zero-halogen requirements (fire-safety zones, railway infrastructure, ventilation-constrained rooms), this avoids the corrosive byproducts of burning halogens. The 'Super resistant K' design variant is Siemens' higher-endurance housing — rated for the full temperature span from -40 °C to +75 °C.