Why Sockets Get Hot, Scorch or Burn, and What to Do About It

Why do sockets get hot?

When current passes through a connection, the higher the resistance at that point, the more heat it produces at the same current. In a sound connection that resistance is negligible. If a socket is getting hot, either resistance has risen somewhere along the current’s path, or the current on the circuit has gone above what the circuit can carry. The causes we find on site are almost always one of these:

• A loose terminal: the screw that clamps the cable end behind the socket works loose over years of heating and cooling. This is the most common cause.
• Worn socket contacts: the metal springs that grip the plug lose tension over time, the plug sits loosely and the contact area shrinks.
• Overload: high-power appliances such as heaters, ovens, irons or kettles run together from the same socket or the same circuit.
• Daisy-chained extension blocks and leads: the entire load passes through the contacts of a single wall socket.
• Undersized cable: a socket circuit wired in 1.5 mm² cable instead of 2.5 mm².
• Moisture: in bathrooms, kitchens and on balconies, oxidised contacts raise resistance.

Why does the breaker not trip when a socket overheats?

A breaker that does not trip while a socket overheats surprises most people, but it is exactly what should be expected. A circuit breaker responds to the current on the circuit, not to heat. A 16 A breaker does not trip until the current goes well above 16 A. A loose connection does not raise the current; it only produces heat at that one point. The entirely normal 9 A drawn by a 2,000 W heater can produce enough heat at a loose connection to melt plastic, and the breaker never sees it.

The RCD does not respond either, because no current is leaking out of the circuit. In other words, none of the standard protective devices in a consumer unit is designed to detect heating at a connection. Arc fault detection devices (AFDDs), which detect the arcing that loose connections produce, do exist, but they are not yet common in homes. So noticing a hot socket is still largely down to you.

What should you do straight away if a socket is hot or smells of burning?

Follow this order. The aim is to stop the risk first and find the cause second:

• If the socket is smoking, crackling or too hot to touch, do not touch the plug; switch off that circuit’s breaker at the consumer unit first.
• If you do not know which breaker feeds the socket, switch off the main switch.
• Once the power is off, pull out the plug.
• Do not use the socket until it has been checked. Keep that circuit switched off if you can; taping over the socket is not a precaution on its own.
• If the cause is overload, other sockets and junction boxes on the same circuit may also have overheated; check those too.

If there is smoke or flame and you cannot safely reach the breaker, call 112. Never use water on an electrical fire.

How much load can a socket take?

In homes, socket circuits are usually wired in 2.5 mm² cable and protected by a 16 A breaker. At 230 V, that means a circuit can in theory carry about 3,680 W. The limit applies not to one socket but to all the sockets on that breaker combined. Running close to it for long periods is not right either; the cable and connections stay hot the whole time.

Approximate ratings for high-power household appliances:

• Electric heater or oil-filled radiator: 1,500–2,500 W
• Kettle: 2,000–3,000 W
• Iron: 2,000–2,800 W
• Hair dryer: 1,800–2,300 W
• Built-in oven: 2,500–3,500 W
• Washing machine or dishwasher while heating water: 2,000–2,300 W

Seen against those figures, it is clear why running a heater and a kettle together from one extension block pushes a circuit over its limit. Giving the oven, dishwasher and washing machine their own circuits solves the problem in a kitchen for good.

What should you watch for with extension blocks and leads?

An extension block does not add capacity to a wall socket; it only divides the same capacity between more appliances. The entire load passes through the contacts of one wall socket and through the extension block’s own cable. So:

• Check the current rating on the extension block’s label. A product rated for only 10 A cannot safely carry more than 2,300 W, even when plugged into a 16 A circuit.
• Do not plug extension blocks into each other.
• Plug heaters, ovens and kettles straight into a wall socket, not into an extension block.
• When using a cable reel with a high-power appliance, unwind the whole cable; cable left coiled on the reel cannot shed its heat.
• Stop using any extension block whose cable runs warm, whose plugs sit loosely or whose casing is cracked.

If a room permanently needs an extension block, what it is really short of is sockets. We fit new sockets and dedicated circuits under our sockets, switches and new circuits service.

Is replacing a scorched socket enough?

Usually not. When a socket overheats, the heat affects not only the plastic body but also the cable end behind it: the copper conductor oxidises, and the insulation hardens or melts. Connect a new socket to that damaged cable end and the same heating soon starts again at the same point.

A proper repair switches off the circuit, cuts the heat-damaged cable back to sound copper, runs new cable from the junction box if needed, makes the connection tight and correct, and replaces the socket with one that has good-quality contacts. The load on the circuit is then reviewed; if overload was the cause, replacing the socket only postpones the problem. We carry out these repairs under our electrical fault finding and repair service, usually the same day within Istanbul.

When should the whole installation be checked?

Heating at a single socket is usually a local problem. The following, however, point to a problem with the installation itself rather than with one connection:

• Heating or scorching at more than one socket, in different rooms.
• An installation more than 20 years old that has never been rewired.
• Socket circuits wired in 1.5 mm² cable, or sockets fed from a lighting circuit.
• A breaker rated too high for the cable it protects.
• Lights flickering or dimming at the same time as the heating.

In these cases we measure the circuits one by one to establish the overall condition of the installation. Deciding whether rewiring is needed only after those measurements protects you from both unnecessary cost and an incomplete repair. We cover installation-wide work on the electrical installation page, and overall installation safety in our electrical installation guide.