Why does my old electrical cable insulation turn to powder when I touch it – Advice from Electriman, North London Electricians

If you have touched an old cable and the plastic or rubbery coating has crumbled away like dry dust or flakes, your wiring has reached the end of its safe working life. This is a very common finding in homes built or last rewired before the 1970s, and it means the insulation that keeps the live conductors safely covered is no longer doing its job.

What causes it to happen?

Electrical cables are insulated with materials designed to last decades, but not forever. Older homes used rubber-insulated cables, sometimes covered in a fabric braid. Rubber naturally dries out over time, losing the oils and compounds that keep it flexible. Heat from years of current flow, exposure to sunlight, contact with certain building materials like lime plaster or mineral wool, and simply the passage of time all speed up this process. Once the insulation degrades, it becomes brittle, cracks, and eventually turns to powder at the slightest touch.

Why is it dangerous?

When insulation breaks down, bare copper conductors can be exposed. Bare live wires in a roof space, wall cavity, or junction box can cause:

1. Electric shock to anyone who touches them

2. Arcing between conductors, which can start a fire inside your walls or ceiling

3. Short circuits that may not trip an older fuse, allowing cables to overheat

What should you do right now?

Do not poke, pull, or further disturb any cable where the insulation looks dry, cracked, or powdery. Switch

Need a qualified electrician in North London?

Electriman covers Mill Hill, Barnet, Finchley, Edgware, Enfield, Watford and surrounding areas. All work is Part P certified and fully insured.