Elastomeric cable insulation materials include a range of rubber and rubber-like compounds used where flexibility, temperature performance, weather resistance or specialist fire behaviour is required.
The table below compares typical properties for common elastomeric compounds. Values are indicative and should be checked against the cable manufacturer’s datasheet for the specific compound and cable construction being specified.
Elastomeric insulation material comparison
| Property | NR / SBR Natural rubber / styrene-butadiene rubber compounds | SiR Silicone rubber | EPR Ethylene-propylene rubber compounds | EVA Ethylene-vinyl acetate copolymer compounds | CR Polychloroprene compounds | CSM Chlorosulfonated polyethylene compounds |
|---|---|---|---|---|---|---|
| Density, g/cm3 | 1.5-1.7 | 1.2-1.3 | 1.3-1.55 | 1.3-1.5 | 1.4-1.65 | 1.3-1.6 |
| Breakdown voltage, kV/mm at 20 °C | 20 | 20 | 20 | 30 | 20 | 25 |
| Specific volume resistivity, Ω cm at 20 °C | 1012-1015 | 1015 | 1014 | 1012 | 1010 | 1012 |
| Dielectric constant, 50 Hz at 20 °C | 3-5 | 3-4 | 3-3.8 | 5-6.5 | 6-8.5 | 6-9 |
| Dielectric loss factor, tan δ | 1.9 × 10-2 | 6 × 10-3 | 3.4 × 10-3 | 2 × 10-2 | 5 × 10-2 | 2.8 × 10-2 |
| Permanent working temperature, °C | -65 to +60 | -60 to +180 | -30 to +90 | -30 to +125 | -40 to +100 | -30 to +80 |
| Short-time temperature, °C | +120 | +260 | +160 | +200 | +140 | +140 |
| Melt temperature, °C | – | – | – | – | – | +160 |
| Flame resistance | Flammable | High flash point | Flammable | Flammable | Self-extinguishing | Self-extinguishing |
| Oxygen index, LOI (% O2) | ≤22 | 25-35 | ≤22 | ≤22 | 30-35 | 30-35 |
| Heating value H0, MJ/kg | 21-25 | 17-19 | 21-25 | 19-23 | 14-19 | 19-23 |
| Thermal conductivity, W/(K·m) | – | 0.22 | – | – | – | – |
| Corrosive gases in case of fire | No | No | No | No | Hydrogen chloride | Hydrogen chloride |
| Radiation resistance, max Mrad | 100 | 50 | 200 | 100 | 50 | 50 |
| Tensile strength, N/mm2 | 5-10 | 5-10 | 5-10 | 8-12 | 10-20 | 10-20 |
| Elongation at break, % | 300-600 | 300-600 | 200-400 | 250-350 | 400-700 | 350-600 |
| Shore hardness | 60-70 (A) | 40-80 (A) | 65-85 (A) | 70-80 (A) | 55-70 (A) | 60-70 (A) |
| Abrasion resistance | Moderate | Moderate | Moderate | Moderate | Medium | Medium |
| Water absorption, % | 1.0 | 1.0 | 1.0 | 1.0 | 1.0 | 1.5 |
| Halogen free | No | Yes | Yes | Yes | No | No |
| Weather resistance | Moderate | Good | Very good | Good | Very good | Very good |
| Cold resistance | Very good | Very good | Good | Good | Moderate | Moderate |
Using the material data
The best insulation compound depends on the complete installation environment. Electrical properties, working temperature, fire behaviour, flexibility, abrasion resistance, weather exposure and halogen content should all be considered together.
For current rating, fault rating and installation design, use the properties and temperature limits stated by the cable manufacturer for the actual cable being installed.