· 3 min read
Every Newtek house wire box carries two numbers: more than 99.95% bare copper, and 101% conductivity. They describe the metal inside the insulation, and they are the main reason one 1.5 sq mm wire runs cooler than another.
Purity
Electrical-grade copper is refined to remove other metals and oxygen. Impurities scatter the electrons that carry current, so they raise resistance. Recycled or mixed copper, which is cheaper, often falls below the purity needed for good conductivity.
IACS conductivity
IACS stands for the International Annealed Copper Standard. In 1913 a reference sample of annealed copper was defined as 100% IACS, and every conductor since is measured against it. Modern high-purity copper conducts slightly better than that old reference, so good copper today measures just over 100%.
A conductor at 101% IACS has about 1% less resistance than the reference copper. Lower resistance means less heat in the wire and less voltage lost along the run.
Why the size on the box is not enough
A wire labelled 1.5 sq mm is only as good as its conductor. If the copper is impure, or the strands add up to less than the stated area, resistance goes up. IS 8130 sets a maximum resistance for every conductor size, which is why it is the real test of a wire, not its label.
How to check
- Buy ISI-marked wire, which is tested against IS 694 and IS 8130.
- Look at the strands: bright, even copper, not dull or patchy.
- Read our guide to checking a genuine coil.