Why does my Hot Tub 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):