# XLPE Cable — Insulation, Rating and Derating

> XLPE cable is power cable insulated with cross-linked polyethylene, a thermoset that does not soften at the temperatures that limit PVC, so it carries more current for the same conductor size. Its usable rating depends on derating for ambient temperature, grouping, installation method and, for buried runs, soil thermal resistivity.

## What it is

Power cable with **cross-linked polyethylene insulation**. The cross-linking
turns a thermoplastic into a thermoset, so the insulation does not soften at
the temperatures that limit PVC.

## Specification at a glance

| Property | Typical specification |
| --- | --- |
| Standard | IS 7098, part by voltage grade |
| Conductor | Copper or aluminium, class stated |
| Continuous rating | 90°C conductor temperature |
| Short circuit | 250°C for a short duration |
| Armour | Steel wire, or aluminium strip on single core |
| Sheath | PVC standard; FRLS where required |

## Derating is the design, not the catalogue

A cable's published rating assumes reference conditions. Real installations
rarely match them, and every departure reduces capacity:

| Factor | Effect |
| --- | --- |
| High ambient temperature | Reduces rating |
| Grouping in a tray or conduit | Reduces rating, significantly when bunched |
| Installation method | Enclosed runs derate more than free air |
| Soil thermal resistivity | Governs buried cable capacity |

Applying these under IS 3961 and IS 732 is what separates a cable that runs
warm from one that runs hot for twenty years and fails early.

## Where projects go wrong

- **Sizing from the catalogue rating** with no derating applied.
- **Bunched cables in a hot shaft**, where the combined grouping and ambient
  factors are severe.
- **Bending radius ignored** during pulling, damaging the insulation invisibly.
- **Single-core cables with steel wire armour**, inducing circulating currents.
- **Gland and armour termination done badly**, so the armour earth path is not
  continuous — an electrical safety defect, not a finish issue.

## Standards referenced

Cable construction under **IS 7098**. Installation practice under **IS 732**.
Current ratings and derating factors under **IS 3961**.

## Frequently asked questions

### Why choose XLPE over PVC insulated cable?

Temperature rating. XLPE operates continuously at 90°C against 70°C for PVC, and withstands higher short-circuit temperatures. For the same conductor size that means more current capacity, or for the same load a smaller conductor — which on a long run is a real saving in copper. XLPE also has lower dielectric losses, which matters on HT distribution.

### What derating factors apply?

Ambient temperature, grouping with other cables, method of installation and, for buried runs, soil thermal resistivity. Indian ambient conditions and crowded cable trays routinely combine to push the applied rating well below the table value — a cable bunched with several others in a hot shaft can end up derated substantially. Sizing from the catalogue figure without applying these factors is the most common electrical design error on fit-outs.

### When is armour needed?

Wherever the cable may take mechanical damage: buried runs, external routes, plant rooms, car parks and any location where trolleys, ladders or vehicles move. Steel wire armour is standard for multicore power cables, while aluminium strip armour is used on single-core cables to avoid circulating currents and heating in the armour.

## Sources

- [IS 7098](https://standards.bis.gov.in/website/published-standards/department-wise) — Cross-linked polyethylene insulated PVC sheathed cables
- [IS 732](https://standards.bis.gov.in/website/published-standards/department-wise) — Code of practice for electrical wiring installations
- [IS 3961](https://standards.bis.gov.in/website/published-standards/department-wise) — Recommended current ratings for cables

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Source: https://hagerstone.com/materials/xlpe-cable