Is it safe to plug one extension lead into another?

What actually goes wrong when leads are chained, why the fuse does not save you, and the two legitimate ways to get power further away.

Difficulty: beginner
Time: 8 min
Read: 4 min
Safety: warning

Short answer

The whole chain is still limited by the single 13A plug at the wall, and every joint adds resistance and a place to overheat or be pulled apart. It also makes the earth path longer and less reliable. For a lamp and a charger it is unlikely to cause harm; for anything meaningful, use a single longer lead or get a socket installed.

Chaining leads feels reasonable because each lead has spare sockets. The mistake is thinking of the sockets as capacity. They are not — the entire chain draws through one plug, one fuse and one flex at the wall, and the joints between the leads are the weakest points in the whole arrangement.

Safety

Every plug-and-socket junction in a chain is a point of contact resistance and a point of mechanical failure, and all of them carry the total load. Daisy-chained leads are a recognised fire cause and are prohibited outright in most workplaces. Do not do it with anything beyond very light loads, and never with heaters, dryers or tools.

Step by step

See the chain as one circuit.Wall socket, plug, flex, socket, plug, flex, socket. The current through the first flex is the sum of everything on every lead in the chain. The last lead's rating is irrelevant to the first lead's temperature.
Understand the resistance problem.Each plug-and-socket junction has a small contact resistance. Three junctions in series means three places dissipating heat, and if any one has worn contacts, that is where the heat concentrates. It is not additive risk, it is compounding.
Understand the earth path problem.The protective earth conductor runs through every one of those junctions too. A poor earth connection is silent — everything works normally until a fault occurs and the earth is the thing that is supposed to carry it.
Understand why the fuse may not save you.The 13A fuse protects against overcurrent in the flex. It does nothing about a hot joint, because a resistive connection dissipating 20W of heat draws no extra current at all. The fuse cannot see it.
Understand the mechanical problem.Chained leads sprawl, get pulled at the joints, and are the arrangement most likely to end up half-unplugged. A plug pulled partly out of a socket while carrying load arcs across a reduced contact area.
Use a single lead of the right length instead.Ten, fifteen and twenty metre leads are cheap and are one continuous flex with one plug. That is the correct answer to "the socket is too far away" for temporary use.
Get a socket installed for anything permanent.If a chain of leads has been in place for months, that is a socket that needs to exist. Adding a socket to an existing circuit in an ordinary room is inexpensive work for an electrician, and it comes with a Minor Works certificate.
Never chain outdoors or in a workshop.Wet ground, tools drawing real current, and mechanical abuse together make this the worst place for chained leads. Use a single outdoor-rated lead or reel, fully unwound, on RCD protection.

Tips

Most workplace electrical safety policies ban daisy-chaining outright. That is not bureaucratic caution — it is based on incident data.
If you find yourself chaining leads to reach, measure the distance and buy one lead that length. It costs less than the two leads you already have.
A chain that includes a coiled reel is worse again, because the reel's coiled rating applies on top of everything else.

Common mistakes

Thinking more sockets means more capacity — The wall plug is the bottleneck for the entire chain regardless of how many sockets appear downstream.
Chaining a lead into a surge-protected strip and assuming it is protected — Surge protection does nothing about overload or contact heating, and cascaded surge devices can interact badly.
Leaving a chained arrangement in place because nothing has gone wrong — Contact degradation is progressive and silent. The first symptom of a failing joint is usually heat you can smell.

If it doesn't work

One of the joints in the chain is warm

Cause: Contact resistance at that plug and socket — Fix: Take the chain apart. That plug and that socket are both suspect and the lead should be replaced.

Things on the far end flicker or reset

Cause: Poor connection somewhere in the chain causing voltage drop — Fix: Replace the chain with a single lead. Flicker means an intermittent connection carrying load.

Fuse in the first lead blows

Cause: Total load across the whole chain exceeds 13A — Fix: Add the wattages. Reduce, or split loads across different wall sockets on the circuit.

RCD trips with the chain in use

Cause: A fault in one of the leads or in an appliance — Fix: Test each lead alone. A lead that trips on its own is faulty and should be discarded.

Questions people ask

Is it ever acceptable?

For a lamp and a phone charger at the far end of a room for an evening, the loads are so small that the risk is minimal. That is not a recommendation, it is a proportion. Anything more than that and the answer is a single lead.

What about plugging a surge strip into a UPS or vice versa?

Manufacturers of both generally advise against it. A UPS should feed loads directly, and a surge strip in front of a UPS can interfere with its input protection.

Is a multi-way adaptor in a socket the same problem?

Similar and often worse. Unfused block and cube adaptors have no fuse of their own, poor contact quality and no strain relief, and they hang out of the socket under the weight of whatever is in them. A fused extension lead is much better than an adaptor.