Extension leads: how to prevent overheating

More sockets do not mean more available power.

The answer in 2 lines. Check the extension lead’s own current or power rating before connecting appliances. Its sockets share that limit: each socket does not get a separate allowance. Never plug an extension into another extension, and fully unwind cable reels before use. Plug portable heaters directly into a suitable wall socket and follow appliance instructions. Stop using anything with scorch marks, damaged insulation, a burning smell or crackling. A fuse or trip switch is no reason to ignore these warning signs.

The first steps

Read the rating: find the maximum load on the lead, reel or instructions. Check appliance labels before combining them; do not guess from the number of spare sockets.
Remove daisy chains: use only one extension device per wall socket. If the lead does not reach, rearrange the equipment safely.
Unwind and inspect: fully unwind a cable reel and check the plug, sockets and cable for damage before using it.

Stop: danger

Burning smell, melting or crackling: stop using the equipment. Switch off the circuit if you can safely reach the consumer unit. Do not handle a hot or damaged plug.
Smoke or flames: get everyone out, stay out and call 999 for the fire and rescue service. Do not use water on an electrical fire.
Repeated tripping: do not keep resetting the circuit or fitting replacement fuses. Have the cause investigated.

Work out what the lead can safely supply

Most extension leads are rated at 13 A, but some older leads and cable reels have lower limits. These are equipment ratings described in current safety guidance checked in 2026, rather than annual statistics. The label on your particular product takes priority.

Compare the combined demand of appliances that could run together with the lead’s stated maximum. If the labels use different units or you cannot establish the limit, avoid that combination and ask for advice. A desk lamp and phone charger create a different demand from a kettle and portable heater, even though both combinations use the same number of sockets.

Choose the connection for the appliance

Connect portable heaters directly to suitable wall sockets. High-demand appliances such as kettles, irons, washing machines and tumble dryers need particular care: follow their installation instructions and avoid sharing an extension with other powerful equipment. A built-in oven or hob may need a dedicated electrical connection, rather than an ordinary plug.

For lower-demand equipment, check the total and the condition of the lead. A surge-protection feature does not increase its load rating. Choose a fused trailing extension rather than a heavy block adaptor that strains the wall socket. The fire brigade’s cables, fuses and leads guidance explains safe combinations and why worn leads should be replaced.

What not to do

Plugging an extension into another extension, including through an extra adaptor.
Running cables beneath rugs, through doorways or anywhere furniture can crush them.
Covering an extension with bedding or leaving it where liquids can spill into it.
Repairing damaged insulation with tape or increasing the fuse rating to stop it blowing.
Using an indoor extension outside.

Cable reels and outdoor use

A wound reel cannot shed heat as effectively as an unwound cable. Follow its separate wound and unwound ratings and fully unwind it before use. Choose a reel with a thermal cut-out, but do not treat that device as permission to overload it.

Outdoor equipment needs a suitable weather-resistant extension and RCD protection. Keep connections dry and position the cable away from cutting tools and traffic. Read the Electrical Safety First extension-lead guidance before choosing or setting up a lead; compare its checklist with the product instructions.

When more wall sockets are the answer

If extensions have become permanent wiring across the room, ask a registered electrician to assess additional sockets. Describe the appliances and where you use them, including equipment likely to run together.

Use Electrical Safety First’s electrician search: enter your postcode and select installation or remedial work. If you rent, report damaged or insufficient electrical provision to your landlord before arranging alterations. The practical precautions apply throughout the UK; tenancy and building requirements differ between nations.

Good to know

A lead can be unsafe because of damage or loose contacts even when its total load is below the label’s maximum.
Check the instructions for every powerful appliance before using an extension; some expressly require a direct wall connection.
Keep the extension accessible so it can be inspected and disconnected without moving heavy furniture.

Illustrative example: in Birmingham, Daniel adds a heater to the extension supplying his desk. He notices a burning smell and stops using it. Once the supply is safely isolated, the damaged lead is taken out of use. He asks for the wall socket to be checked and arranges a suitable direct connection for the heater before using it again.

A made-up story, for illustration.

Bobby

Sources, verification, confidence

Verified on 4 November 2026, for England. Confidence: high for load ratings, avoiding daisy chains, cable-reel precautions and warning signs. The safe load and permitted use of a particular product depend on its label and instructions; no single wattage limit is applied to every extension.