---
title: "Copper or aluminium: where aluminium stops being cheaper"
description: "Aluminium needs 1.6 times the cross-section for the same current — and still costs less per metre. The crossover, and the four places it goes wrong."
date: "2026-03-15"
author: "Divakar B"
source: "https://energycalchq.com/blog/copper-vs-aluminium-cable-cost"
license: "© 2026 Divakar B. Quote with attribution to https://energycalchq.com/blog/copper-vs-aluminium-cable-cost"
---

Every cable schedule of any size reaches this argument. Aluminium is a fraction
of the price of copper per kilogram, so an aluminium cable should be cheaper. It
usually is — but not always, and the size at which it stops being cheaper is
higher than most people assume.

The honest answer is that aluminium wins on the big feeders and loses on the
small circuits, and the crossover is not really about the metal price at all.
It is about terminations.

## Start with the physics

Aluminium conducts about 61 % as well as copper. To carry the same current at
the same temperature rise you need roughly **1.6 times the cross-sectional
area**. Working from typical armoured cable tables:

| Copper | Rating | Nearest aluminium | Rating |
|---|---|---|---|
| 25 mm² | 92 A | 50 mm² | 108 A |
| 50 mm² | 138 A | 70 mm² | 136 A |
| 70 mm² | 174 A | 120 mm² | 190 A |
| 95 mm² | 210 A | 150 mm² | 218 A |
| 185 mm² | 318 A | 300 mm² | 339 A |

The jump is not free. That extra area means a fatter cable, a larger gland, a
bigger termination, more tray width and a larger bending radius.

But here is the part that surprises people: **it is still lighter**. Aluminium
is a third the density of copper, so even at 1.7 times the area an aluminium
conductor weighs about half as much per metre. On long runs that changes how the
cable is handled, what it costs to pull and what supports it needs.

![Comparison of 70 mm² copper against 120 mm² aluminium for the same 174 A duty](/blog/copper-vs-aluminium-comparison.png "Equivalent ratings, not equivalent sizes. Volt drop comes out almost identical because the extra area cancels the poorer conductivity.")

Volt drop is the pleasant surprise. Compare equivalent-*rated* sizes rather than
equal areas and the mV/A/m figures land within a few per cent of each other. The
extra cross-section aluminium needs for its current rating also fixes its
resistance. Sizing by current and then checking volt drop, as in the
[cable sizing calculator](/tools/cable-size), you will rarely find aluminium
pushed up a size that copper was not.

## Where aluminium clearly wins

**Long runs of large cable.** Submains, transformer-to-panel feeders, incoming
services, the run to a distant pump house. Anything from about 95 mm² copper
equivalent upwards, over any real distance, and the metal saving dwarfs
everything else.

**Overhead and outdoor distribution.** Weight per metre governs pole spacing and
sag. This is why the DISCOM's network outside your gate is aluminium and always
has been.

**Anywhere theft is a risk.** Copper on an open site walks. Aluminium is worth
too little to be worth cutting down.

## Where aluminium loses

**Final circuits and small sizes.** Below about 25 mm² the metal saving is
trivial in absolute terms, and everything else about aluminium gets harder. Small
aluminium conductors are mechanically fragile, they do not tolerate repeated
bending at terminations, and the accessories often are not rated for them.

**Anywhere with many terminations.** This is the real crossover, and it is a
labour question, not a metal question. Every aluminium termination needs to be
done properly — and "properly" means more steps than copper:

- The oxide layer must be wire-brushed off and joint compound applied
  immediately. Aluminium re-oxidises in minutes, and aluminium oxide is an
  insulator.
- The lug must be rated for aluminium, or bimetallic where it meets a copper
  busbar. An aluminium conductor bolted directly to copper in a damp panel is a
  galvanic cell, and it corrodes.
- The joint must be torqued to specification, with Belleville washers, and
  **re-torqued** after the first thermal cycles. Aluminium creeps under sustained
  pressure; a joint that was tight on commissioning day can be loose in a year.

A feeder with two terminations amortises that effort over a hundred metres. A
distribution board with forty outgoing ways does not.

**Tight spaces.** If the cable has to fit an existing tray, duct, gland plate or
bending radius, the 1.7× area can simply make aluminium impossible. Retrofits
inside an existing containment are frequently a copper job regardless of price.

## The comparison people get wrong

Comparing a copper cable and an aluminium cable of the **same size** — 70 mm²
copper against 70 mm² aluminium. That comparison is meaningless: they do not
carry the same current, so they are not alternatives for the same circuit.

The valid comparison is between two cables that do the same job. Price a
120 mm² aluminium cable against a 70 mm² copper cable, both delivered, both
with their glands, lugs and labour, and both derated for the same installation
conditions. Anything else is comparing two different circuits.

Do the same on the total installed cost, not the cable price:

| Include | Because |
|---|---|
| Cable, per metre delivered | The obvious one |
| Glands and lugs | Aluminium needs larger, and often bimetallic |
| Termination labour | The hidden cost — bigger for aluminium |
| Tray or duct width | The extra area has to go somewhere |
| Handling and pulling | Aluminium is lighter — a genuine saving on long runs |
| Re-torquing at first maintenance | A real cost, and skipping it is a fire risk |

## What about the losses?

Since the two options are sized to the same current rating, their resistance per
metre is similar, and so is their energy loss. This is one comparison that is
usually a wash.

It is worth checking on a heavily loaded, continuously running feeder though.
If aluminium lands you *just* above the required rating while copper lands you
comfortably above it, the copper option may run cooler and lose less. Work out
the loss in kWh a year and price it — on a feeder running 8,000 hours it can be
a larger number than the cable price difference.

## Not all aluminium is the same aluminium

The aluminium in a modern cable is usually not the pure EC-grade metal that
gave aluminium wiring its reputation in the 1970s. Building-wire aluminium is
now typically an **8000-series alloy**, developed specifically to fix the
failure mode that caused the trouble.

The original problem was creep. Pure aluminium under sustained clamping
pressure flows away from the load, so a joint tightened correctly on
commissioning day loosens by itself, heats, oxidises and eventually fails.
8000-series alloy has far better creep and elongation behaviour, and modern
connectors are designed and tested around it.

This matters when you are reading old advice. "Aluminium terminations are
unreliable" was true of a particular metal in particular connectors, and it is
why the practices in the previous section exist — but a properly made
termination on 8000-series conductor into an AL-rated lug, torqued to
specification with Belleville washers, is a joint you can expect to last.

What has not changed is that it is unforgiving of shortcuts. Copper tolerates a
sloppy termination for years. Aluminium does not.

## Why the price you were quoted moves

Both metals trade on the London Metal Exchange, and the conductor is a large
share of a cable's cost — larger for copper, which is why copper quotations go
stale faster.

Three consequences worth planning for:

- **Quotations have a validity period** for a reason. On a long procurement,
  the copper price at order can differ materially from the price at tender.
- **The crossover moves.** The point at which aluminium becomes the cheaper
  installed answer shifts with the metal ratio, so a rule that held on last
  year's project may not hold on this one. Reprice, do not assume.
- **Aluminium is more stable in absolute terms** simply because there is less
  money in the metal. On a large fixed-price contract, that predictability is
  worth something on its own, separately from the headline saving.

## A working rule

| Situation | Choose |
|---|---|
| Under 25 mm² equivalent | Copper |
| Final circuits, socket outlets, control | Copper |
| Many terminations per metre of run | Copper |
| Submains and feeders over 50 mm² equivalent | Aluminium, usually |
| Long runs, few terminations | Aluminium |
| Retrofit into existing containment | Whatever fits — usually copper |
| Outdoor, overhead, theft-prone | Aluminium |

There is no single crossover size, because it depends on your labour cost and
the metal price on the day you buy. What does not change is the shape of the
decision: **the metal saving scales with length, and the extra cost scales with
the number of terminations.** Divide one by the other and the answer usually
becomes obvious without a spreadsheet.

Size the circuit first, in copper and in aluminium, with the derating and volt
drop that apply to your route — the [cable sizing
calculator](/tools/cable-size) will do both — then price the two complete
installations. Deciding on metal price alone is how a job ends up with forty
aluminium terminations in a distribution board and an electrician who will
remember you.