Helpful video reference. Electrical Safety First is the UK's leading electrical safety charity. Their short safety guide "Extension leads | STAY SAFE | ELECTRICAL SAFETY FIRST" covers the main risks clearly and is a useful watch before explaining any of this to other people in the house.
1. Match the lead's current rating to the load
Extension leads sold in the UK are marked with a current rating, usually 10A or 13A. To find the current your appliances will draw, add up their wattages and divide by 230. A 2,000 W convector heater draws about 8.7A. Add a 1,200 W kettle and you are at 14A, over the limit of a standard 13A lead.
If the lead has a surge-protected tower with multiple sockets, the total current rating still applies across all the sockets combined. Four people plugging in laptops and phone chargers will be fine. A kettle, microwave, and toaster all at once will not be.
2. Check the cable cross-section for longer leads
Extension leads come in various cable gauges. The packaging should state the conductor cross-sectional area in mm2. Standard leads typically use 1.0mm2 conductors, which is adequate for most domestic use at short lengths. For leads over 10m supplying anything above about 2,000 W, choose 1.5mm2 conductors to keep volt drop within acceptable limits.
Volt drop is not just an efficiency issue. Some appliances, particularly variable-speed tools and battery chargers, can run hotter than normal on a low voltage supply, shortening their lifespan or triggering protection circuits.
3. Do not run leads under carpets or through doorways
Running an extension lead under a carpet is one of the more common causes of electrical fires in UK homes. The carpet insulates the cable, preventing heat from escaping. The carpet backing and underlay are flammable. The lead is walked on, which damages the insulation without anyone noticing until the bare conductors short against each other.
Through a doorway is almost as bad. Repeated pinching of the cable at the door frame cracks the insulation over time. If you need power on the other side of a room or a wall, you need a properly installed socket, not a lead threaded through a gap.
4. Use an RCD if working outdoors
Taking an extension lead outside puts the cable on damp ground, near water, and in the path of garden tools. If the cable is cut by a lawnmower or strimmer, or develops a fault in wet conditions, the current will travel through whatever path is available, which might be you.
A 30 mA RCD trips in under 40 milliseconds, fast enough to prevent a fatality in most cases. If the outdoor socket is already on a circuit protected by the RCD in the consumer unit, you are covered. If you are bringing an indoor lead outside, plug a 30 mA RCD adapter into the indoor socket first, then connect the lead.
5. One lead, one wall socket
Plugging one extension lead into another, or into a multi-socket adapter, means the first socket has to supply the total current for everything on the chain. The socket on the lead is not designed for this. The contact resistance at that joint generates heat under load, and with enough load over enough time it will fail, sometimes dramatically.
If you need more sockets in one spot, either use a single long lead back to the wall, or get a proper socket fitted. A double socket in place of a single one is usually a half-hour job.
6. Know when a lead is past its useful life
There is no legal maximum age for an extension lead. In practice, any lead that shows these signs should be replaced: discolouration around the plug or sockets (indicates past overheating), a socket that feels loose or does not grip a plug firmly, cracking in the sheathing anywhere along the cable, or an obvious kink where the cable has been bent sharply and repeatedly. These are not cosmetic issues; they indicate that the insulation is compromised.
When to call us
The honest truth is that a permanent extension lead is almost always the wrong solution. If there is a fixed spot where a lead lives all the time, that spot needs a real socket. Richard adds sockets across Sandwich and east Kent - a single extra socket is often done in under an hour, and a properly wired socket is far safer and tidier than a lead trailing across the floor.
Need an extra socket fitted?
Richard adds sockets to rings and radials throughout east Kent. Small jobs at £10 per 10 minutes, no call-out fee for the Sandwich area.
Contact Richard