Extension leads: the rules nobody reads

The 13-amp budget

A standard UK socket, plug and extension lead all top out at 13 amps, which at mains voltage is roughly 3,000 watts. That is the budget. Everything on the lead shares it, and the lead does not care how many outlets it offers: a four-gang lead is four sockets and one budget, an invitation rather than a promise.

Heat is what spends the budget fastest. Anything whose job is making heat (kettles, heaters, irons, toasters, tumble dryers) draws kilowatts, while electronics sip. A kettle alone runs about 3kW: the entire budget in one appliance. A phone charger is around 20W; you could run dozens, in theory.

The rules nobody reads

Rule one: heaters and kettles go straight into the wall, never into a lead. Rule two: never plug one extension lead into another. Daisy-chaining multiplies sockets without multiplying capacity, and every extra junction adds resistance, which is to say heat. Rule three: a lead on a reel gets fully unwound before heavy use, because coiled cable traps its own warmth; the reel’s label says so, in small print nobody reads either.

Surge protection deserves an honest sentence too: a surge-protected lead shields electronics from brief voltage spikes, which is useful under a desk of computers, and it does nothing whatsoever about overload. The 13-amp budget applies to the fanciest lead in the shop.

When the answer is more sockets

If a room lives on extension leads, the room is telling you something. Adding a double socket is a small electrician job (as a guide, £100–£200 depending on the cable run) and it retires the trailing-lead assault course along with the overload risk. A dead socket taken out by a chronically overloaded lead is a cheap lesson by electrical standards, but it is still a lesson.

Outdoors is a stricter discipline again: outdoor-rated leads, RCD protection and a hard stop at the first drop of rain. The garden power guide covers it, and the wider home electrics guide maps where extension culture ends and proper wiring begins. Plug fuses have their own small print as well: the small appliance guide explains the 3A, 5A and 13A logic in two minutes.