What performance criteria distinguish fire - resistant cables from flame - retardant variants, and how do their structural designs address distinct safety requirements?

Q: What performance criteria distinguish fire - resistant cables from flame - retardant variants, and how do their structural designs address distinct safety requirements?   A: Fire - resistant cables prioritize circuit continuity during combustion, employing specialized materials like mica tape wraps and heat - stable copper conductors to maintain functionality for defined durations (typically 1–3 hours) under 950–1000°C flame exposure. This design ensures critical systems such as emergency lighting and fire alarms remain operational during building evacuations. In contrast, flame - retardant cables focus on limiting fire propagation through halogen - free or low - smoke additives that suppress flame spread and toxic gas emission, though they may fail electrically once insulation reaches thermal degradation thresholds.   Structural differences are pronounced: fire - resistant models integrate multiple protective layers including intumescent barriers that expand to insulate conductors, while flame - retardant versions rely on modified polymer compounds with self - extinguishing properties. Installation environments dictate selection—fire - resistant cables suit escape routes and life safety systems, whereas flame - retardant types are standard in general building wiring to minimize fire growth potential. Both categories undergo rigorous testing, with fire resistance validated through temperature - time curve exposure and flame retardancy measured via vertical flame spread indices.