# Blue, red, yellow: how do you read a P17 socket?

> Colour, number of pins, earth position: how to tell the voltage and supply type of a P17 socket (IEC 60309 standard) at a glance.

Source: https://www.darkside-energy.com/en/did-you-know/reading-a-p17-socket/ · Dark Side Energy · Updated: 2026-10-27

27 October 2026 · 2 min read

- The colour shows the voltage: blue for 230 V, red for 400 V, yellow for 110 V.
- The number of pins shows the supply type: 3 for single-phase, 5 for three-phase with neutral.
- The position of the earth pin acts as a key: a plug designed for another voltage will not fit.

At an event, [P17 sockets](https://www.darkside-energy.com/en/glossary/#p17) are everywhere: distribution cabinets, power boxes, extension leads. “P17” is the common French name for the industrial plugs and sockets of the IEC 60309 standard. Even before reading the label, three clues tell you what you are dealing with: the colour, the number of pins and the position of the earth pin.

## The colour shows the voltage

- **Blue**: 200 to 250 V, the usual 230 V.
- **Red**: 380 to 480 V, three-phase 400 V.
- **Yellow**: 100 to 130 V, the 110 V found, for example, on building sites in the United Kingdom.

The standard provides for other colours, which are rarer at events: black for 500 to 690 V, violet or white for extra-low voltage.

## The number of pins shows the supply type

- **3 pins**: phase, neutral and earth, for single-phase.
- **4 pins**: three phases and earth, for three-phase without neutral.
- **5 pins**: three phases, neutral and earth, for three-phase with neutral.

## The earth pin acts as a key

The earth pin is the largest one, and its position varies with voltage and frequency. It is read like the hand of a clock, relative to the keyway: 6 o'clock for the usual blue 230 V and red 400 V sockets. A plug designed for another voltage has its earth at another hour: it simply will not go in.

Colour, pins and keying work together: a red 400 V plug will not fit a blue socket, and a three-phase plug will not fit a single-phase socket. The system protects the equipment, and the people who plug it in.

## What about the rating?

The [rating](https://www.darkside-energy.com/en/glossary/#calibre) (16, 32, 63 or 125 A) is marked on the socket and shows in its size: the higher it is, the bigger the socket, and a 32 A plug will not fit a 16 A socket. To find out how much power each rating can deliver, read [How much power can you draw from a P17 socket?](https://www.darkside-energy.com/en/did-you-know/p17-socket-power/)

> Blue means 230 V. Red means 400 V. And if the plug will not go in, this is not the time to force it.

Which socket for your equipment? The calculator suggests the right socket and cable.

[Open the electrical calculator](https://www.darkside-energy.com/en/electrical-calculator/#conversion)

[Why do LEDs trip RCDs?](https://www.darkside-energy.com/en/did-you-know/leds-and-rcds/)

## A project? Let's talk power.

Venue, dates, known requirements: tell us about your event and we will get back to you quickly.

[Request a quote](https://www.darkside-energy.com/en/contact/)
[contact@darkside-energy.com](mailto:contact@darkside-energy.com)