Why does my plug get warm?

What causes a plug or socket to become hot or damaged?

If you are at all concerned that a plug or socket is becoming warm/hot or damaged in any way, stop using the appliance immediately. 

Loose Plug Fuse Clips

Over time due to the current drawn, the clips holding the fuse inside plugs supplying relatively high power appliances such as hot tubs, garden heaters and electric vehicles can become slightly loose. The loose connection generates heat, the heat increases the resistance of the connection, which in turn generates even more heat. Eventually the temperature can rise to the point that the plug starts to melt.

The picture below is from a hot tub, and shows the classic signs of a loose fuse; the fuse holder itself has melted, and there is a brown mark and/or cracks appearing on the socket due to the heat. The clue that the socket has been damaged by an over-heating plug fuse holder, is in the position of the brown mark, which mirrors the position of the fuse in the plug.

 

Overloaded Plug 

Another cause of the same damage detailed above is more than 2,900W being connected to a 13A plug. People assume that a 13A plug can take just that - 13A (3,000W). However, in reality the maximum safe limit is 12.6A (2,900W) and only for a short period of time, such as when boiling a kettle. Over longer periods loads as high as 2,900W will lead to the plug becoming warm. For this reason, hot tubs and electric vehicle chargers in the UK normally have a maximum power of 10A  (2,300W), as this is a safe limit for prolonged use.

Corroded Pins

The pins on the plug should be clean and shiny in appearance. If they are dull or corroded, this will increase the resistance of their contact with the socket. They can be easily cleaned using fine emery paper or wire wool. The socket may be visibly damaged around where the pins enter it.

Loose Connection within the Socket

Over time, the metal contacts within the socket which mate with the plug pins can become slightly loose. The loose connection generates heat, the heat increases the resistance of the connection, which in turn generates even more heat, until the contacts do not effectively clip around the plug pins. Unlike with a loose plug fuse, the brown marks/cracks on the socket will not mirror the position of the fuse. They may instead be around where the pins enter the socket.

How do I check the fuse contacts?

Checking that the plug fuse contacts tightly hold the fuse on an annual basis, or if you are at all concerned about the plug becoming warm can, help prevent issues from occurring. 

Moulded Plugs and RCD Plugs

Follow the steps below if your plug looks like these (the process is exactly the same as that pictured for an RCD plug, as both have the same fuse cover):

         

Moulded plug               RCD plug

 

1    Switch off the appliance and remove the plug from the socket.
2 Find the fuse holder, which will be small plastic rectangle labelled 'FUSE' or 'FUSED' in between the live and neutral pins. 
3 Use a small flat blade screwdriver to carefully lift up the fuse holder. If the fuse contacts are tightly holding the fuse, then it can take a little force to lift the cover. If it falls out very easily, then the contacts have likely become loose.
4      Check the contacts (little springy U shaped clips) and the metal on the fuse for any signs of heat damage. Heat will cause the metal to turn darker, sometimes with a multicoloured pattern. The plastic may also be melted, particularly around the contact.
5         Check that the fuse is the correct rating for the appliance - hot tubs and EV will normally use 13A. Check that the fuse is genuine (see Counterfeit fuses below). You may need to slide the fuse out of the holder to check.
6 Use a small flat blade screwdriver to push in each side of both contacts - more than 1mm is unlikely to be needed. Do not push them too close together, as the fuse still needs to fit.
7 With the fuse back in the holder, place it so that it is resting back on the plug. Firmly press until the holder is fully inserted, flush with the surface of the plug.


Rewireable Plugs

Follow the steps below if your plug looks like this. Instead of a visible fuse holder like a moulded plug, it will have screws:

1      Switch off the appliance and remove the plug from the socket.
2 Use a Pozidrive or Phillips screwdriver to unscrew the larger screw which is in the centre of the plug. Do not unscrew the two smaller screws which are nearer where the cable enters the plug. Lift off the plug cover.
3 Use a small flat blade screwdriver to carefully lift up the fuse, to remove it from the contacts. If the fuse contacts are tightly holding the fuse, then it can take a little force and 'pops' outs. If it falls out very easily, then the contacts have likely become loose.
4 Check the contacts (little springy U shaped clips) and the metal on the fuse for any signs of heat damage. Heat will cause the metal to turn darker, often with a multicoloured pattern. The plastic may also be melted, particularly around the contact.
5       Check that the fuse is the correct rating for the appliance - hot tubs and EV will use 13A. Check that the fuse is genuine (see Counterfeit fuses below).
6 If the contacts are loose, gently push them together using your thumb and finger. No more than 1mm closer together is likely to be needed.
7 Push the fuse back into the clips, ensuring that it is positioned correctly. The outer edge of each clip should align with the ends of the fuse.
8 Place the plug cover back on, and press down firmly. Re-tighten the central screw, to fix it back into position.

 

What can I do if it is already damaged?

If a standard 13A plug is damaged, it can be cut off and replaced by someone who is confident and competent to do so. We would only recommend using a high quality heavy duty for high current appliances, such as the Permaplug which can be purchased here.

EV granny chargers often have a temperature sensor in the 13A plug- seek advice, as the plug cannot be replaced. In some cases it may be possible to replace with a new flex/plug assembly.

If an RCD plug is damaged it must be replaced by another RCD. For anything other than a hot tub/swimming pool, 30mA RCD plugs are widely available.

For hot tubs, it is vitally important that it only replaced with a 10mA RCD. 10mA plug RCDs are not available in the UK, but it can be replaced with an in-line RCD using our conversion kit. This has the added bonus that it will also solve the issue of the bulky unit.

 

Counterfeit Fuses

Unfortunately counterfeit fuses are becoming increasingly common within the UK, and are readily for sale on popular online market places. Listings for these two are currently on the largest UK shopping site, with one even having a 'choice' endorsement.

  

They are also being found by Trading Standard teams fitted to otherwise compliant items being imported. This section has been added following a 20A fuse (identical to the top right picture) recently being found in the plug of a hot tub. Fake fuses may not blow at the required limit, leading to the appliance cable over-heating. If they do blow, as many are not filled with sand, they can explode causing irreparable damage to the plug and socket. This video illustrates some of the dangers during a test.

Characteristic Genuine Counterfeit
Ceramic body colour

Off white/cream.

Brighter white.

Metal end caps

Dull or slightly shiny metal with a small dimple. No fuse wire should be visible between the cap and the ceramic body.

Very shiny metal.

Larger dimple.

Fuse wire may be visible between the cap and the ceramic body.

Printing appearance Matt. May be gloss.
Printing colour 3A dark red, 13A brown. 3A may be an orange/red.
Rating Most commonly 3A and 13A. Cannot exceed 13A. May have a dangerously high rating above 13A, often 15A or 20A. Anything higher than 13A is a definite counterfeit.
Length 25.4mm (+/- 0.6mm). Often shorter than 25.4mm.
Weight 2.2g or more Under 2.2g. Lower weight indicates that the fuse is not filled with the required quartz sand. Fuses without sand may violently explode causing damage.
Approval Marks

 

Marked 'Approved to BS1362'

ASTA and BSI logos are clear and correct.

Often still claim to comply with BS1362.

Often may have ASTA and BSI logos, although subtle errors such as the 'S' being the wrong way around on the BSI mark are sometimes made.