PVC is rated to 70°C, XLPE to 90°C — giving XLPE a 15–25% higher current rating for the same cable size. LSOH is mandatory where fire-safe, halogen-free cable is required. This guide covers the differences, BS EN 50575 CPR classes, and how to specify the right cable for every application.
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The insulation and sheathing material of a cable determines its temperature rating, fire performance, and suitability for different environments. Three types dominate UK electrical installations: PVC (polyvinyl chloride), XLPE (cross-linked polyethylene), and LSOH (Low Smoke Zero Halogen). Each has distinct properties that affect where and how it can be used under BS 7671:2018+A4:2026 and the Construction Products Regulation (CPR).
Cable selection is governed by BS 7671 Section 522 (selection and erection with respect to external influences) and Section 422 (protection against fire). Since July 2017, the CPR requires cables permanently installed in buildings to carry a reaction-to-fire classification under BS EN 50575.
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PVC (polyvinyl chloride) is the most widely used cable insulation in UK domestic and commercial installations. Standard twin and earth (6242Y), SY control cable, and most flexible cords use PVC insulation and sheathing.
PVC Fire Performance Warning
PVC releases hydrogen chloride gas when burned. HCl is toxic and highly corrosive — it destroys electronic equipment and is hazardous in escape routes. In locations where fire safety requires minimal toxic gas emission, PVC must not be used.
XLPE (cross-linked polyethylene) is produced by chemically cross-linking polyethylene polymer chains, dramatically improving its thermal stability. XLPE is the standard insulation for power cables, armoured submain cables (SWA), and medium-voltage distribution cables.
Elec-Mate's cable sizing calculator applies the correct current rating tables for XLPE-insulated cables, with derating for grouping, ambient temperature…
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LSOH (Low Smoke Zero Halogen) cable uses a halogen-free polymer compound — typically a polyolefin mixture — for both insulation and sheathing. When burned, LSOH cable produces minimal visible smoke and does not release corrosive halogen gases. This is critical in enclosed public spaces where dense toxic smoke would impede evacuation.
The conductor temperature rating is the key factor in determining current-carrying capacity. Higher temperature ratings allow more current for the same cable size:
| Insulation Type | Continuous Temp | Rating vs PVC |
|---|---|---|
| PVC | 70°C | Baseline (Tables 4D) |
| XLPE / EPR | 90°C | ~15–25% higher |
| Silicone | 150–180°C | High-temp industrial only |
When derating for high ambient temperature, the derating factor (BS 7671 Appendix 4 Table 4B) differs between PVC and XLPE cables because the reference temperature and allowable temperature rise are different. Always use the correct column for the cable insulation type when applying ambient temperature derating.
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Start free trialThe Construction Products Regulation (CPR) requires cables permanently installed in UK buildings to be UKCA or CE marked with a reaction-to-fire classification. The classes under BS EN 50575:2014+A1:2016 are:
Cable selection must be recorded on the EIC schedule of test results — the cable type and insulation material are required entries. When working on public buildings or commercial projects, check the specification for CPR class requirements before ordering cable. Installing PVC where LSOH (Cca or better) is specified is a non-compliance that could result in the installation failing the handover inspection.
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Elec-Mate's cable sizing calculator applies the correct current rating tables for PVC and XLPE cables, with automatic derating. 7-day free trial, cancel anytime.
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