Halogen-free cable compounds are used where the fire behaviour of the cable is important, especially where corrosive gases and smoke toxicity need to be reduced. These compounds are commonly associated with LSZH cable designs.
The table below compares typical properties for non-cross-linked and cross-linked halogen-free polymer compounds. Values are indicative and should be checked against the manufacturer’s datasheet for the actual cable compound being specified.
Halogen-free compound comparison
| Property | H Not cross-linked halogen-free polymer compounds | HX Cross-linked halogen-free polymer compounds |
|---|---|---|
| Density, g/cm3 | 1.4-1.6 | 1.4-1.6 |
| Breakdown voltage, kV/mm at 20 °C | 25 | 25 |
| Specific volume resistivity, Ω cm at 20 °C | 1012-1014 | 1013-1014 |
| Dielectric constant, 50 Hz at 20 °C | 3.4-5 | 3.4-5 |
| Dielectric loss factor, tan δ | ~10-3 | 10-2-10-3 |
| Permanent working temperature, °C | -30 to +70 | -30 to +90 |
| Short-time temperature, °C | +100 | +150 |
| Melt temperature, °C | >130 | – |
| Flame resistance | Self-extinguishing | Self-extinguishing |
| Oxygen index, LOI (% O2) | ≤40 | ≤40 |
| Heating value H0, MJ/kg | 17-22 | 16-25 |
| Thermal conductivity, W/(K·m) | 0.17 | 0.20 |
| Corrosive gases in case of fire | No | No |
| Radiation resistance, max Mrad | 100 | 200 |
| Tensile strength, N/mm2 | 8-13 | 8-13 |
| Elongation at break, % | 150-250 | 150-250 |
| Shore hardness | 65-95 (A) | 65-95 (A) |
| Abrasion resistance | Medium | Medium |
| Water absorption, % | 0.2-1.5 | 0.2-1.5 |
| Halogen free | Yes | Yes |
| Weather resistance | Medium; good in black compounds | Medium; good in black compounds |
| Cold resistance | Average | Average |
When halogen-free compounds are useful
Halogen-free compounds are often selected for buildings, tunnels, public areas, transport systems, control rooms and other locations where reduced corrosive gas emission is important during a fire.
Material selection should consider the whole cable system, including required operating temperature, flame performance, smoke requirements, mechanical strength, installation environment and any CPR or project-specific fire performance classification.