The Critical Distinction: Fire-Resistant vs Flame-Retardant
These two properties are regularly confused, and the confusion can have life-safety consequences:
- Flame-retardant (FR) cable is designed to limit fire propagation. When ignited, it will self-extinguish once the ignition source is removed, preventing the cable from becoming a conduit for fire spread through a building. FR cable does not maintain electrical function during a fire — once the outer jacket and insulation burn, the circuit fails.
- Fire-resistant (circuit-integrity) cable is designed to maintain electrical function during a fire for a specified time period, even while the cable is exposed to direct flame. The circuit must continue operating so that fire alarms can alert occupants, emergency lighting can illuminate escape routes, and sprinkler controls can activate suppression systems.
A cable can be both flame-retardant AND fire-resistant, but they are not the same property. For emergency systems, circuit integrity is the specification requirement. Standard LSZH or FR cable does not meet this requirement regardless of its flame-spread performance.
Why Mica Is the Key Material
Standard polymer insulations (PVC, XLPE, LSZH) all burn when exposed to direct flame above their ignition temperatures. Once the polymer burns away, the bare conductor is exposed and the circuit fails. Mica (a naturally occurring mineral) does not burn — it remains intact as a solid insulation layer even at temperatures exceeding 1000°C, maintaining electrical isolation between conductors during a fire.
Fire-resistant cable constructions use a layer of mica tape (typically wrapped around each conductor, or around the conductor bundle) as the primary fire-survival insulation. A fiberglass braid is often added over the mica for mechanical protection. The outer jacket (PVC, LSZH, or silicone) provides everyday protection but is expected to be consumed in a fire — the mica layer carries the circuit through.
BS 6387: The Dominant International Standard
BS 6387 is the British Standard for performance requirements for cables required to maintain circuit integrity under fire conditions, and it is the most widely referenced standard for this cable type globally. The standard defines three test categories applied in combination:
| Category | Test Condition | Temperature | Duration |
|---|---|---|---|
| C | Direct flame + mechanical shock (vibration) | 650°C | 3 hours |
| W | Flame + vibration + water spray | 650°C | 3 hours |
| Z | Extreme high-temperature flame | 950°C | 20 minutes |
| CWZ | All three tests — highest rating | 650°C + 950°C | 3h + 20min |
A cable marked BS 6387 CWZ has passed all three categories — it maintained circuit integrity through 3 hours at 650°C with mechanical vibration, through water spray while on fire, and through 950°C flame for 20 minutes. This is the highest rating under the standard and is required for the most critical life-safety applications.
IEC 60331: The Parallel International Standard
IEC 60331 is the international (ISO/IEC) standard for fire-resistant cables, using a different test approach than BS 6387:
- IEC 60331-1: tests cables for circuit integrity at 750°C for 90 minutes (no mechanical vibration)
- IEC 60331-2: tests cables for circuit integrity at 830°C for 90 minutes (no vibration)
- IEC 60331-21/23/25: specific test methods for different cable sizes
The IEC tests do not include mechanical shock (vibration) or water spray, which means BS 6387 is considered more comprehensive and is preferred in specifications that anticipate real fire conditions where cables may be physically disturbed by building collapse or firefighting water.
UL 2196: North American Circuit Integrity
In North America, UL 2196 covers cables that maintain circuit integrity under fire conditions. The standard covers 2-hour circuit integrity testing at temperatures that simulate a standard UL fire exposure curve. Cable listed under UL 2196 is required for critical fire alarm and emergency communication circuit wiring in buildings following NFPA 72 (National Fire Alarm and Signaling Code) and NFPA 70 (NEC) requirements in the US.
The GN500, GN800, GN1000 Product Series
Shanghai Unicorn's fire-resistant cable range is organized by operating temperature:
- GN500 — mica + fiberglass braid, rated 500°C, 500V, suitable for fire alarm and emergency lighting circuits in standard fire conditions. BS 6387 C rating.
- GN800 — double-layer mica tape with fiberglass overbraid, rated 800°C, 800V. BS 6387 C/W rating for applications combining high temperature and water spray exposure.
- GN1000 — pure nickel conductor with mica and high-temperature construction, rated to 1000°C for 3 hours. BS 6387 CWZ. Required for tunnel emergency circuits, nuclear facilities, and installations with the highest fire severity expectations.
Installation Requirements for Fire-Resistant Cable
Specifying the right cable is only part of the equation. Installation method significantly affects whether the cable will actually maintain circuit integrity in a fire:
- Fire-rated fixings and supports — standard plastic cable clips will melt in a fire, dropping the cable and potentially breaking the circuit. Fire-resistant cable installations require metal fixings and supports rated for the fire exposure temperature.
- Separation from non-fire-resistant circuits — fire-resistant cable should not be bundled with standard cable in the same tray or raceway. A fire that burns through standard cable insulation can create shorts that affect adjacent fire-resistant circuits.
- Fire-rated junction boxes and terminations — the circuit integrity is only as good as the weakest link. Terminations, junction boxes, and connectors must be rated for the same fire exposure as the cable.
Frequently Asked Questions
What is the difference between fire-resistant and flame-retardant cable?
Flame-retardant cable limits fire propagation — it self-extinguishes when the ignition source is removed. Fire-resistant (circuit-integrity) cable maintains electrical function during a fire for a specified period. For fire alarms and emergency lighting, circuit integrity is the critical property — FR cable alone is not sufficient.
Is LSZH cable fire resistant?
No. LSZH is a jacket compound that reduces toxic smoke and eliminates halogen gas during a fire — it is a smoke toxicity property, not a circuit integrity property. LSZH cable will burn and lose electrical function in a fire. Fire-resistant mica cable can also use LSZH jacketing, but circuit integrity comes from the mica layer, not the LSZH jacket.
What BS 6387 category is required for fire alarm cable?
BS 5839-1 typically requires cable meeting at least BS 6387 Category C (650°C, vibration, 3 hours) for fire alarm circuits. Enhanced installations may specify CWZ. Always confirm with the project's fire safety engineer and local building regulations, as requirements can differ by building type and jurisdiction.
GN500 / GN800 / GN1000 Fire Resistant Cable — Factory-Direct
Shanghai Unicorn manufactures mica fire-resistant cable in GN500 (BS 6387 C), GN800 (BS 6387 C/W), and GN1000 (BS 6387 CWZ) ratings. Pure nickel conductors available for maximum temperature performance. Factory-direct pricing with test certificates on request.