Power cables guide: XLPE vs PVC, copper vs aluminium, armoured vs unarmoured

Power cables carry electricity from transformers and panels to every motor, machine and distribution board on a site. They are buried, pulled through trays and left in place for decades. A cable that is undersized, wrongly specified or substandard can overheat, cause voltage problems or start a fire, and replacing it later is expensive and disruptive.

This guide explains how low-voltage (LV) power cables are described and how to specify them.

Reading a cable description

A typical description looks like this: 3.5 core × 95 sq mm, aluminium, XLPE insulated, armoured, PVC sheathed, 1.1 kV. Each part means something:

• Number of cores: 2, 3, 3.5, 4 or more conductors. The "half" core in 3.5 core is a reduced-size neutral.
• Cross-sectional area (sq mm): the conductor size, which decides how much current it can carry.
• Conductor material: copper or aluminium.
• Insulation: the material around each conductor, usually PVC or XLPE.
• Armour: steel wire or strip protection, if any.
• Outer sheath: the overall protective layer.
• Voltage grade: 1.1 kV for most LV distribution.

Copper vs aluminium conductors

• Copper conducts better, so a copper cable can be smaller for the same current. It is more flexible, easier to terminate and less prone to connection problems. It costs more.
• Aluminium is lighter and cheaper, so it is common for large-size distribution cables. It needs larger sizes for the same current and careful termination with the right lugs to avoid loose, overheating joints.

Many projects use aluminium for large feeder cables and copper for smaller final circuits and control wiring.

PVC vs XLPE insulation

• PVC insulation is economical and widely used. Its maximum continuous conductor temperature is typically around 70 °C.
• XLPE (cross-linked polyethylene) handles higher conductor temperatures, typically around 90 °C, so an XLPE cable of the same size can carry more current. It also has better electrical properties and resistance to moisture.

For larger power cables, XLPE is now the usual choice.

Armoured vs unarmoured

• Armoured cables have a layer of galvanised steel wire or strip that protects against mechanical damage. Use them for direct burial, outdoor runs and areas where cables can be hit or crushed.
• For single-core cables carrying AC, non-magnetic (aluminium) armour is used to avoid heating from induced currents.
• Unarmoured cables are lighter and cheaper, suitable for protected routes such as cable trays inside buildings or conduits.

Fire performance

For buildings, hospitals, metros and data centres, the cable's behaviour in a fire matters:

• FR (flame retardant) sheaths resist the spread of flame.
• FRLS (flame retardant low smoke) cables also limit smoke and acid gas.
• LSZH or LS0H (low smoke zero halogen) cables emit very little smoke and no halogen gases, protecting people and equipment.
• Fire survival cables keep working in a fire for a specified time, for emergency systems.

Sizing a cable

A cable must be sized for three things:

1. Current-carrying capacity: the cable must carry the load current continuously without overheating. Capacity depends on installation method (in air, on trays, buried, in ducts), ambient and ground temperature, and how many cables are grouped together. Grouping and high temperatures reduce capacity, so derating factors apply.
2. Voltage drop: long cable runs lose voltage. Motors and equipment need voltage within limits, so long runs often need a bigger cable than current alone suggests.
3. Short-circuit capacity: the cable must survive the fault current until protection trips.

Your electrical consultant should calculate the size. Give suppliers the result, not just the load.

Standards and quality

In India, LV power cables are made to standards such as IS 1554 (PVC insulated) and IS 7098 (XLPE insulated), and conductors to IS 8130. Buy ISI-marked cables from licensed manufacturers.

Substandard cables are a real problem: conductors that are thinner than stated, or with fewer strands, carry less current and overheat. Check:

• Conductor resistance against the standard's maximum value, which is the best single test of conductor quality.
• Insulation and sheath thickness.
• Printing on the sheath: manufacturer, size, voltage, standard, ISI mark and length marking.
• Routine test certificates for each drum, and type test reports for the design.
• For large orders, third-party inspection at the factory.

Drum lengths and logistics

Cables are supplied on drums. Ask for standard drum lengths, or specific cut lengths to reduce joints and waste. Check drum weight and size for handling and transport.

A specification checklist

1. Voltage grade.
2. Number of cores and size.
3. Conductor material and type (stranded, compacted).
4. Insulation (PVC or XLPE).
5. Armour type or unarmoured.
6. Sheath type and fire performance (FR, FRLS, LSZH).
7. Standard (for example IS 7098 Part 1).
8. Quantity, drum lengths, delivery location and date.
9. Tests and inspection required.

Frequently asked questions

Why is XLPE cable preferred for power distribution?

XLPE insulation tolerates a higher conductor temperature than PVC, so the same size cable can carry more current. It also has better electrical properties and moisture resistance.

Is aluminium cable safe?

Yes, when sized correctly and terminated with the right lugs and techniques. Most problems with aluminium cables come from poor terminations, not the conductor itself.

When do I need armoured cable?

Use armoured cable for direct burial, outdoor runs and anywhere the cable could be damaged mechanically. Unarmoured cable suits protected routes like trays and conduits.

How do I spot substandard cable?

Check the conductor resistance against the standard's maximum, the number and size of strands, insulation thickness and the sheath printing. Buy ISI-marked cable from licensed manufacturers and ask for routine test certificates.

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