Why Silicone for Wire & Cable
Silicone rubber rated 105 °C (UL 3122) to 180 °C (UL 3212) continuous — 3× higher than PVC delivers heat resistance that no common thermoplastic insulation can match over the same service life. Flame retardant by nature: silicone is self-extinguishing and produces non-toxic SiO₂ ash on combustion, whereas PVC releases hydrogen chloride gas. This halogen-free behaviour satisfies the LSZH (Low Smoke Zero Halogen) requirements now mandatory in rail, shipbuilding, and data-center wiring codes. Flexibility is retained at −60 °C without plasticisers — critical for EV battery wiring harnesses and arctic-service cabling where PVC becomes brittle and cracks.
Compound Types
| Type | Cure System | Temperature Rating | Key Use |
|---|---|---|---|
| HTV (mill-processable) | Peroxide (DCBP, DCP) | 150–180 °C | Extruded cable jacket, wire insulation |
| LSR (liquid) | Pt addition | 105–150 °C | Injection-molded connectors, boots |
| Silane-crosslink XLPE | Moisture crosslink (VTMS/VTEOS) | 90–105 °C | Low-cost power cable, low-voltage |
HTV compounds are processed on open mills or internal mixers, then extruded over conductors using a crosshead die and vulcanised in a continuous vulcanisation (CV) tube with hot air or steam. LSR is injection-moulded for precision connector components. Silane-crosslinked XLPE is the dominant insulation for low-voltage distribution cable in developing markets, blending polyethylene economics with meaningful temperature upgrading.
Peroxide Cure System for HTV Cable Compounds
DCBP (dicumyl peroxide, also labelled DCP) is the standard peroxide for extruded HTV cable applications. It activates at 160–180 °C, giving good scorch safety during mixing and extrusion while delivering a dense, uniform crosslink network. Typical DCP loading is 1.0–2.5 phr on rubber weight, balanced against the target modulus, elongation, and electrical properties.
Post-cure is essential: 200 °C × 4 h in a forced-air oven removes volatile peroxide decomposition byproducts — acetophenone and α-methyl styrene — that otherwise remain trapped in the insulation. Residual byproducts degrade electrical tracking resistance and can cause long-term degradation of dielectric strength.
A-171 (vinyltrimethoxysilane) or VTEOS is used for the silane-crosslink XLPE route. Applied at 0.5–2.0% on PE weight, the silane grafts onto the polyethylene backbone under peroxide initiation, then moisture crosslinks in a steam or warm-water bath to build the final network without a CV tube.
Key Standards
| Standard | Scope | Temp Rating |
|---|---|---|
| UL 3122 | Silicone rubber insulated wire | 150 °C, 600 V |
| UL 3212 | High-temp silicone wire | 200 °C |
| IEC 60245-4 | Flexible cords, silicone rubber insulation | 180 °C |
| GB/T 12528 | Chinese HV silicone cable | 110 kV |
Compliance with UL 3122 or UL 3212 is required for North American market access. IEC 60245-4 covers European flexible cord applications. GB/T 12528 governs the highest-voltage silicone cable applications in the Chinese grid and specifies both electrical and mechanical requirements for 35–110 kV rated cables.
Related Reading
HTV Silicone Rubber · Silicone Rubber for Cable Insulation · A-171 Vinyltrimethoxysilane