Is copper the best electrical conductor?
Where the claim comes from
Copper is everywhere electricity goes: house wiring, motors, transformers, data centres. It’s also one of the metals I track every day on the Markets board, because cable makers live and die by its price. So it’s easy to assume it must be the best conductor there is.
What’s actually true
- Copper is the yardstick. In 1913 the International Electrotechnical Commission adopted the International Annealed Copper Standard (IACS). Annealed copper at 20 °C is defined as 100% IACS (58 MS/m), and every other metal is rated against it. Modern high-conductivity copper routinely reaches 101–102% IACS.
- Silver beats it. Pure silver is about 106% IACS, the most conductive metal. It isn’t used for ordinary wiring because it’s expensive and mechanically weak, so it stays in specialist uses like contacts.
- Gold is worse, not better. Gold is about 70% IACS. It’s used on connectors because it doesn’t corrode, not because it conducts well.
- Aluminium is the other big one. Pure aluminium is about 61% IACS, but it’s much lighter and cheaper per amp carried. That’s why overhead transmission lines are mostly aluminium conductor, while copper dominates cables, buildings and machines.
The truth
The truth: Copper isn’t the best conductor. It’s the best conductor you can afford by the tonne, and that’s why its price is a barometer for the whole electrical industry. When copper gets expensive, engineers reach for aluminium, never for silver.