Plug wiring colour scheme

UK plugs use brown insulation for the live wire, blue insulation for the neutral wire and green with yellow stripes insulation for the earth wire.

But why this particular combination of colours? The answer is deceptively simple: there is no type of colour blindness that will result in these wires becoming confused.

Above: how a UK plug looks to someone who is red-green colourblind.

Above: how a UK plug looks to someone who is blue-yellow colourblind.

One of the lesser-known safety features of a UK plug is the extra distance that the neutral wire has to travel when compared to the live wire. If someone pulls on the mains cable the live wire will disconnect first, making the plug safer.

Under the IEC 60446 standard only black, brown, red, orange, yellow, green, blue, violet, grey, white, pink and turquoise are acceptable colours for labelling wires. Countries must choose an appropriate selection of colours that eliminates the possibility of confusion.

IEC 60446 colours. From top to bottom: normal vision, deuteranopic vision, tritanopic vision.

During the course of writing this post I realised that there are no copyright-free high-resolution photographs of the inside of a UK plug available online. I hereby release the image below into the public domain.

Click to enlarge.

21 thoughts on “Plug wiring colour scheme

  1. Nice article; hadn’t thought about the colour -blindness issue. I always assumed that blue and brown were used so it was easy to remember which wire went where in the plug. b(L)ue – left and b(R)own – right.

  2. Its also fairly illogical given the names of the terminals

    A live wire we think of as blue/white – electric blue even – the colour of sparks & electricity – who associates brown with live wires or electricity??

    earth/soil is brown, so why isn’t the earth the brown one?

    alternatively brown (or grey) could be the neutral one as they are the basic neutral colours.

    But that would make things too easy wouldn’t it?

  3. What if there is White, Blue and Black? Which one is the live, the neutral and the earth?

  4. I have a light the wiring is purple and orange which is live and which is neutral

  5. There’s no system I know of that uses red, black and brown. Is it possible that the brown wire used to be green and has faded or decayed over time?

  6. I have a black & white wires which pins do they fit on a 3 pion plug

  7. It might be a good idea to update (or replace) this article to add pictures showing how the old red/black/green standard holds up under the same photographic manipulations. At the moment we just have your word for it (oh, and all the other places making the same claim). It would force the point home if you showed both.

  8. I wish I had a photo of black/red/green flex on a BS1363 plug for you. Sadly, I do not. I expect somebody, somewhere still has such flex in a junk box. Maybe John Ward or Big Clive or PhotonicInduction (all youtubers who play with electrical stuff, often to destruction, especially PhotonicInduction).

    The reason I mentioned it was John just did a video about terminology and colour changes. So I just left a comment on that video, and maybe he’ll read the comment and maybe he has some of the old flex kicking around.

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