The physics, briefly
Copper's resistivity is about 1.7 × 10⁻⁸ Ω·m; aluminium's is about 2.7 × 10⁻⁸ Ω·m — roughly 60% higher. To carry the same current with the same loss, an aluminium conductor needs a larger cross-section than a copper one.
Aluminium is far lighter, though: about a third of copper's density. So even with the bigger cross-section, an aluminium winding usually weighs less, and aluminium costs less per kilogram.
What that means for the transformer
The choice ripples through the whole design:
- Size: an aluminium-wound unit can be somewhat larger for the same rating.
- Weight: it is often lighter, which helps where units are carried or pole-mounted.
- Price: aluminium usually brings the price down.
- Joints: aluminium needs correct jointing technique; poor joints are where problems start.
How to compare two quotes
Do not choose on the metal alone. A well-designed aluminium winding can outperform a poorly designed copper one. Ask for the same rating, the same voltages, and — where available — the losses at no load and full load. Those numbers decide your running cost over the years.
General guidance only — every installation is different. For work on live equipment, use a licensed electrician. Last reviewed 28 September 2026.