XLPE (cross-linked polyethylene) is the dominant insulation material for medium voltage power cables worldwide. If you're specifying cable accessories — terminations, joints, or connectors — they need to be compatible with XLPE's specific properties. This guide explains what XLPE is and how to match accessories to your cable construction.
Why XLPE Is the Standard
XLPE dominates MV cable insulation for three reasons:
Higher temperature rating. XLPE operates continuously at 90°C (short-circuit at 250°C) versus 70°C for PVC. This allows higher current-carrying capacity in the same conductor size.
Better dielectric properties. XLPE has a dielectric strength of 20-25 kV/mm and very low loss factor. This allows thinner insulation for the same voltage rating, reducing cable weight and cost.
Moisture resistance. The crosslinked molecular structure resists water treeing — a degradation mechanism that affects non-crosslinked polyethylene in wet environments.
All ZZ cable accessories are designed and type-tested for XLPE insulated cables per GB/T 12706.4 and IEC 60502-2.
Matching Accessories to Cable Construction
An XLPE cable has four layers, and each layer requires restoration or connection at a termination or joint:
| Cable Layer | Function | Accessory Component |
|---|---|---|
| Conductor (Cu/Al) | Current carrying | Compression or bolted lug |
| XLPE insulation | Electrical insulation | Insulation tube (stress-graded) |
| Metallic screen | Earth fault path | Screen connection / constant force spring |
| Outer sheath | Mechanical/moisture | Sheath tube (adhesive-lined for sealing) |
The critical component is the stress control at the point where the screen is cut back. The electric field concentrates at this transition, and without proper stress grading, partial discharge occurs even with adequate insulation thickness. This is why cable accessories are not just "tubes" — they include semiconductive stress control layers that must be precisely matched to the cable geometry.
Heat Shrink vs Cold Shrink for XLPE
Both technologies are fully compatible with XLPE cables and are type-tested to the same standards. The choice is operational:
Heat shrink (NRSY/WRSY/JRSY) uses crosslinked polyolefin that contracts when heated. Best for: dry conditions, budget-sensitive projects, long storage requirements.
Cold shrink (TLS/NLS/WLS/JLS) uses pre-stretched silicone that contracts when the core is removed. Best for: hazardous areas, wet weather, confined spaces, emergency repairs.
Both achieve ≤2 pC partial discharge in type testing — well below the 20 pC limit.
FAQ
Can I use XLPE-rated accessories on EPR cables?
In most cases, yes. EPR (ethylene propylene rubber) has similar dimensions and electrical properties to XLPE at the same voltage class. However, always verify that the accessory's conductor range and insulation diameter match the EPR cable's actual dimensions, which may differ slightly from XLPE.
What is water treeing and do accessories prevent it?
Water treeing is a degradation mechanism in polymeric cable insulation caused by electrical stress in the presence of moisture. It appears as tree-like patterns of micro-voids in the insulation. Accessories don't prevent water treeing in the cable itself, but properly sealed accessories prevent moisture from entering at joints and terminations — the most vulnerable points.
Do I need to specify the cable manufacturer when ordering accessories?
Not usually. Accessories are designed to cover a range of cable dimensions within each voltage class. However, if your cable has unusual insulation diameter or screen construction, provide the cable datasheet to our engineers and we'll confirm compatibility.
Written by Long, Sales Engineer at ZZ Heat Shrink. For complete MV cable accessory specifications, see cable accessories. For a quotation, contact our engineers.