Limitations Due to High Performance:
Extremely High Cost: Materials (e.g., mica tape) and processes are complex, making it one of the most expensive types of civilian cables.
Large Outer Diameter and High Rigidity: The addition of the fire-resistant layer significantly increases the cable's outer diameter and stiffness, raising installation difficulty and space requirements.
Current-Carrying Capacity Requires Adjustment: Due to the thermal insulation of the fire-resistant layer, the long-term allowable current-carrying capacity for the same cross-section typically requires multiplication by a correction factor of less than 1.0 (e.g., 0.7–0.85). This must be considered during design and selection.
Application Scope:
Used for ultimate protection circuits mandated by national fire safety regulations, powering particularly critical firefighting facilities, emergency evacuation systems, and life safety systems. Installed in the highest-risk areas, such as extremely crowded spaces or locations with difficult evacuation conditions.

Conductor: Copper. May use special stranding structures (such as compacted round) to facilitate fire-resistant layer coverage. Cross-sectional range typically from 1.5 mm² to 300 mm² (larger cross-sections are more challenging to achieve fire-resistant properties).
Fire-resistant layer (core feature): Double or multiple layers of mica tape (or other mineral-insulated fire-resistant materials) must be wrapped around the conductor. This is the physical foundation for achieving the "N" function.
Insulation: Cross-linked polyethylene (XLPE), long-term allowable operating temperature 90°C.
Sheath: Polyolefin material, meeting halogen-free and low-smoke requirements.
Rated voltage: 0.6/1kV (most common).
Long-term allowable operating temperature: Maximum conductor temperature: +90°C.
Short-circuit temperature (5 seconds): Maximum +250°C.
Fire resistance performance: Core parameter. Must pass GB/T 19216 or IEC 60331 standard tests, with common requirements including: maintaining circuit integrity under flame impact and water spray for 90 minutes in flames at 750°C to 950°C (fire resistance code: NH-IA90).
Combustion performance rating: B1 grade - Must simultaneously meet all stringent requirements of GB 31247 for B1 grade (including combustion calorific value, heat release, smoke density, smoke toxicity, etc.).
Halogen-free performance: pH value ≥ 4.3, conductivity ≤ 10 μS/mm.
Low smoke performance: Smoke density and other indicators meet B1 grade requirements.