Wiring Question (4 wires?)

Accomodation, House and Garden
1
Hello,

I searched all over this forum, but could not find any answer to this one. I'm looking to install a lighted cabinet in the bathroom of our new apartment. I've installed dozens of lights before and there have only ever been three wires: Blue neutral, Brown live and Green/Yellow ground.

I'm puzzled because in our bathroom there is an extra Black wire? Any idea what this is for?

https://ibb.co/GT7Rp67

2
Is there an extractor in the bathroom which may be triggered by operating the light switch ?

3
Black wires are generally “hot/live” - the mirror in our bathroom has a sensor to turn on from motion. It has a similar set up as what you describe. I’d never seen one before and couldn’t figure out why “the light was always on until I found the sensor on the lower left side of the mirrors glass. It’s a small oval, and if there was enough motion from the door opening, or a hand waved over it, it went on.

4
Thats for the cctv camera...

5
It could be that the black wire is permanently "hot" while the blue one is controlled by a switch. This way you could connect one of those cabinets which have both a light and a power socket (neutral and ground would be shared).

Could you open the closest switch to see how the connections are made there? As an alternative, you could use a tester* and operate all the switches (including those in the main fuse box) to see when each wire has current.

* a real multimeter would be better than a screwdriver with light bulb...

6
It is common to have 3-phases in Switzerland

3 Phases - colour codes used in my place:

- Black

- White

- Red

But then it is also a fact that electricians use every colour under the sun for 'Switched' live.

I suspect the black is such a switched live.

Often there is a covered box in the ceiling you can open. also check the switches in the room to see the colours of wires there (unless you have KNX/EIB then it's more complicated).

Hope this helps

7
As it is for a bathroom cabinte:

Yelow-Green: Earth.

Blue: Neutral.

Brown: Switched live (for the light)

Black: Live (for a socket, racer outlet)

(Function of black and brown could be swapped).

A live blue colored wire, when there is a green-yellow earth? Run for the hills! Who knows what else is crazy in that house.

If earth is yellow-green, a (light) blue wire must be neutral !

If earth is yellow-green, there must be no green wire.

If earth is yellow-green, and there is a ligh blue wire, there must be no yellow wire.

Historic and current wire colors:

http://toolbox.electrosuisse.ch/_fil...gen_Teil_4.pdf

8
Yes, but only in the kitchen (we have two separate 3P circuits in the kitchen) or workshop, never in the bathroom!

Tom

9
Depends, many washing machines use 2 or 3 phases and could be installed in a bathroom. But the location does not make sense for multiple phases.

But most likely it is a switched live. Easy to test, connect a light (blue + black, and separately or with another light: blue + brown). Then try the switches in the room. Also if you take to cover off the light switch and peak behind you will probably see the colours used.

Blue = Neutral

Black/Brown = Live / Switched Live

Green/Yellow stripped = Earth

10
You're right, my mistake - I wrote "blue" instead of "brown". A bad error, apologies to the OP!

In the picture there's yellow/green, blue, brown and black wires.

Of course the blue should be neutral...

11
I have seen very pale blue used for a switched live, so be careful.

Generally speaking you should normally find earth, neutral, live/switched live at any electrical 'space'.

But I have also seen no earth for an oven installation etc... so always if in doubt be cautious.

If you don't have the competence then call an expert. If a fire or other accident happens you could have issues claiming on your insurance. Or someone could get seriously hurt

12
Am I the only one who shudders when I see questions about electricity/wiring posted on EF? If you have to ask here, you don't know what you are doing, and you should be calling a qualified electrician.