Extension leads and adaptors: the items most likely to fail
The lead under the desk is often the least cared-for item in the building and the one doing the most work.
Why leads fail
These are the faults that turn up most often on extension leads and adaptors:
- damage to the outer sheath of the cable, often where it has been trapped under a desk leg or a door
- cable pulled loose where it enters the plug, so the coloured inner wires are visible
- cracked sockets or plugs
- scorch marks or discolouration, a sign of overheating
- tape used to repair or join cables
- a nail, foil or wire in place of a fuse
Every one of these is visible. A weekly glance at the leads in each room catches most of them before they become dangerous.
Overloading
A standard four-way extension lead is rated at 13 amps in total, not 13 amps per socket. That is roughly 3,000 watts. A kettle alone can use most of it, so a kettle and a heater on the same lead is an overload. Check the wattage on each item's rating plate and add them up. Electrical Safety First has a free online socket overload calculator that does the sums for you.
Daisy-chaining
Electrical Safety First's advice is one extension lead per wall socket, never one plugged into another. Daisy-chaining stacks more load onto the first lead and the wall socket. If you are doing it because there are not enough sockets, that is a sign the room needs more sockets, which is a job for an electrician.
Cable reels
A cable reel only reaches its rated current when it is fully unwound. Wound up, the cable cannot shed heat, and Electrical Safety First warns that running a reel in its wound state can make it overheat and catch fire. Unwind it completely before running a heater, a pressure washer or power tools, and choose reels with a thermal cut-out.
Block adaptors
Plug-in block adaptors sit directly in the wall socket, where their weight and the leverage of the plugs in them can loosen the connection and make it run hot. A bar-type extension lead on a cable avoids that. If you do use a block adaptor, choose a fused one and keep the load low.
How leads are tested
HSE treats extension leads, multi-way adaptors and connecting leads as portable appliances. They get user checks, a formal visual inspection and a combined inspection and test, at intervals that depend on what they supply and where. At a test visit, each lead is counted and labelled as its own item, and surge-protected strips count as leads too.
Sources
Common questions
Do extension leads need PAT testing?
Yes. HSE treats extension leads, multi-way adaptors and connecting leads as portable equipment, with user checks, visual inspections and testing like any other item.
How much can I plug into a four-way extension lead?
No more than 13 amps in total, which is about 3,000 watts across all four sockets. A kettle or a heater can use most of that on its own.
Is a surge protector the same as an extension lead?
For testing purposes, yes. It is counted and tested as a lead. The surge protection does not stop it being overloaded or damaged.
Related guides
How to prepare for a PAT test
A practical checklist for the day of your PAT test, plus a free appliance register and user-check sheet to download. Saves time and keeps your quote accurate.
Read the guideClass I and Class II appliances: what is the difference?
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