I am renovating my cellar. The electrician wired the room a couple of years ago and until now i´ve not had the money or time to finish it off. I was looking at the wiring for the wall sockets today and realized that for every box there is at least 8 wires stuffed into it separated into 2 groups of wires. 1 group of wires has 5 colours...brown, black, grey, green/yellow and blue, the other group had green/yellow, blue and brown. I mostly have double sockets so this setup is then repeated for the second socket next to it. How do I install the socket...what is grey? My wall socket has only 3 input holes...so what do I do?

Thanks for any advice.

  • What coutry are you in? Wiring color conventions vary around the world.
    – Hank
    Jan 11 '15 at 18:56
  • Hi..I´m in germany.If I attatch green/yellow as earth, blue as Neutral und Brown as live..what do I do with the others? Jan 11 '15 at 19:00
  • OK...So I´ve kind of worked out that Black,Grey and brown are all live wires. Do I isolate them or stick them all into the socket? Jan 11 '15 at 19:13
  • 1
    Don't put all three in, instead, pick one for each socket, and insulate off those you're not using. In theory, any of the three live phases should work, and should be loaded evenly Jan 11 '15 at 20:50
  • I would definitely ask a local electrician to at least help figure out what the plan was originally. Jan 13 '15 at 4:32

Do NOT touch the 3 hot wires together. From what I have heard, unlike the US, Germany provides full 3 phase power to residences. That means those three hot wires are each 120 degrees out of phase with each other, so touching them will create a short circuit. If you use a multimeter to measure the voltage from one to the other, you should see somewhere around 200 volts, and 220 between any one of them and neutral/ground. Regular outlets in Europe are 220 volts, so they are only wired to one of the three phases, and neutral. Different outlets should each use a different phase so the load is roughly balanced between the phases.


If you're Europe, those are the standard colours for 3 phase wiring. It may be the electrician had some spare and used that instead. I'd suggest testing the black and grey wires aren't live (and insulate them off), and continue to use the brown as live, blue as neutral and green/yellow as earth.


What country and what type of service do you have? Colors can mean different things in different regions, and the electrician may or may not have follow standard color schemes. But regardless, you should be able to figure out what the wires do by tracing them back to the source. You are correct - only 3 wires are needed for a basic wall outlet (hot, neutral, ground). You can find basic info about coloring schemes here. The important rules (for the US) are: hot=black (and connects to the bronze colored terminal on the outlet), neutral=white, and neutral-green (or green/yellow).

There are several main reasons why there can be more than 3 wires:

  • outlets are cascaded, i.e. there is an incoming and an outgoing wire with 3 conductors each, one continuing to the next wall box)
  • there can be a switched circuit and an always-on circuit (where one incoming wire is connected to a wall switch as opposed to a direct connection to the circuit breaker)
  • there could also be a separate circuit for an appliance like a washer/dryer/fridge/oven - you will find it in the service box based on colors
  • there could be a separate circuit connected to a GFI switch

Check for these things by locating the wires, based on colors, in other wall boxes for outlets and switches, or in the service panel.

ps: ok, now that we know you are in Germany, much of what I said does not apply (about colors and GFI, which is not optional and not distributed in Europe). But the basic process for identifying each wire remains the same.

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