How to Check an Extension Lead for Damage

Checking an extension lead takes about ninety seconds and needs no tools. Unplug it, look closely at the plug and the socket block, then run the whole cable through your fingers feeling for nicks, flat spots, kinks and heat damage. Anything that exposes copper, wobbles, smells burnt or has gone brittle means the lead is finished, and no amount of tape makes it safe again.

Start at the plug

Unplug the lead from the wall first, and if it has just been running a heater or a compressor let it cool, because warm PVC feels supple even when it has been cooked and is about to crack.

The plug top takes more abuse than any other part because people yank leads out by the cable. Look for these:

• Cracks in the plug body, particularly around the pin bases and along the seam where the two halves meet.
• Loose or bent pins. Try to wiggle each pin. It should feel solid. A pin that moves is a pin that will arc.
• Discolouration on the pins. Blackened brass around the live and neutral pins means arcing at the socket, usually from poor contact or overloading.
• The cable grip. Tug the cable gently where it enters the plug. If the sheath slides even slightly, the strain relief has failed and the conductors are taking the load.
• The fuse carrier. If it is missing, cracked or has been bridged with anything other than a proper BS 1362 fuse, stop there.

Moulded plugs cannot be opened, so if the moulding is damaged the whole lead goes.

Work along the cable

This is where most faults hide. Pay the lead out fully and run it slowly through a loosely closed hand, feeling as much as looking. You are hunting for:

• Nicks and cuts in the outer sheath. If any colour of inner insulation shows through, the lead is damaged even if it still works perfectly.
• Flat or crushed sections from a car wheel, a workbench leg or a door. Crushing squashes the insulation between the conductors.
• Stiff or brittle patches. Healthy PVC is supple, so a section that has gone hard and crackly is heat damaged and will split.
• Tight kinks and corkscrewing, which usually mean the copper strands inside have already started to break.
• Melted or glossy spots from contact with a heater, a hot exhaust or a work lamp.
• Previous repairs. Tape and connector blocks are not acceptable repairs on a flexible lead.

Now the socket block

Turn the socket end over and look into each outlet. Brown scorch marks or a smell of hot plastic mean arcing has already happened, and that lead should not go back into use. Check that the shutters covering the live and neutral holes still spring back when you press the earth hole with something insulated, because shutters that stay open are a real hazard around children and around metal swarf in a workshop.

Press each socket face and each switch too. Anything that rattles, sits proud or feels spongy suggests the internal contacts or the plastic mounting have broken. A switch that needs jiggling before its neon lights is a failing contact, not a failing neon.

Cable reels need extra attention

Reel type leads fail in two extra places. Check the cable where it passes through the drum exit, since that spot takes constant flexing. Then watch for flickering power or a burning smell when the drum is partly wound, which points at the slip ring assembly inside. Reels also carry two ratings, wound and fully unwound, and running near full load while coiled cooks the cable from the inside, so inspect the inner turns on any reel that has been run hot. Our guide on why extension leads get hot covers that side of it.

What testing adds

A visual check catches most faults, but it will not find a broken earth conductor inside intact insulation. If the lead feeds anything with a metal case, a socket tester plugged into each outlet is a cheap way to confirm earth continuity and polarity. A multimeter on continuity does the same job: earth pin to earth contact should beep, live to earth should not. Workplaces formalise this as PAT testing, which adds an insulation resistance test.

When to bin it rather than repair it

Scrap the lead outright if you find exposed conductors, a cracked plug or socket body, scorching or melting anywhere, a cable that has been cut and taped, a loose pin, or brittle insulation. Flexible leads are cheap and the failure mode is fire or shock, so the maths is not close. Cut the plug off before it goes in the bin so nobody retrieves it.

Fitting a new rewireable plug is fair enough if the damage sits right at the plug end and the rest of the cable is sound. Cut well past the damaged section and make sure the outer sheath, not the individual cores, is what the cable grip clamps.

How often to check

Before every use for anything dragged around a site, a garden or a garage floor. Every few months for leads that live permanently behind a desk, since those fail from overloading and dust rather than knocks. Always check after a lead has been run over, trapped, pulled hard from a socket or used outdoors in the wet.