Insulated Copper Wire Grades Explained

Cable with the insulation still on is bought as insulated copper wire, and the grade is a percentage: roughly how much of the cable’s weight is copper. The rest is plastic. The higher the percentage, the more the cable is worth per kilo.

The four grades

• 20%: thin cable where the plastic outweighs the metal by a wide margin, such as data cable, phone cable, ribbon and thin flex.
• 40%: everyday cable, such as appliance cords, extension leads and mixed household cable.
• 75%: thick power cable and industrial wiring.
• 83%: the heaviest power cable, from industrial power distribution.

How to tell which yours is

Cut a clean end and look at it. If the copper fills most of the cross-section and the insulation is a thin skin, it is one of the high grades. If you see a few fine strands in a thick plastic jacket, it is 20%. Weight helps too: copper is heavy, so a short length of high-grade cable feels heavy for its size.

If a load is mixed, sort it thick from thin. A bag of mixed cable is graded on what is actually in it.

What these grades do not take

• Aluminium-core cable. The conductor is silver, not copper-coloured. Keep it apart and ask us about it.
• Fibre optic cable. There is no copper in it.
• Cable with heavy steel armour.
• Car wiring looms. These go as car wire, a grade of their own.

Should you strip it?

Stripped clean, copper wire is bright copper, the top copper grade. It is usually worth stripping thick cable and rarely worth stripping thin. Our guide to getting copper out of wire goes through it.