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I'm currently trying to change my lamp in my bathroom so I disconnected my current lamp and forgot to write down what the cables were attached to.

There are 3 cables coming out from the ceiling.

-----------------------
      /  |  \
     /   |   \
    /    |    \
   /     |     \
Brown   Blue   Black

Between Brown + Black I get voltage.

Between Brown + Blue I get voltage.

Between Blue + Black I get no voltage.

How can I tell which of these cables are ground (AC 230V)?

Is there any way of measuring resistance/current/voltage to tell what is ground here?

Please let me know if I can provide any more information.

I'm from Sweden, usually ground is green-yellow here.

There are two lamps connected to the dimmer so the circuit is split somewhere in the wall.

I ended up connecting blue to neutral and brown to live. Works like a charm. Read Winny's comment below for more detailed information.

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  • \$\begingroup\$ Can you provide a picture of the lamp and tell us what country you are ? Wiring standards vary \$\endgroup\$
    – Warren Hill
    Commented Apr 12, 2020 at 7:29
  • \$\begingroup\$ Which country you are in? Because AC mains wiring has color standards. It differs from country to country, but as you got 230VAC its not US at least. Usual wiring colors in Europe are Brown = Live, Blue = Neutral, Green-Yellow = Protective Ground. \$\endgroup\$
    – NStorm
    Commented Apr 12, 2020 at 7:30
  • \$\begingroup\$ @WarrenHill Hi, unfortunately the wiring from the dimming-outlet is split to another lamp aswell, so I don't think that's gonna help. I'm from Sweden. Usually ground is green/yellow. But there's no such cable. \$\endgroup\$
    – Joel
    Commented Apr 12, 2020 at 7:30
  • \$\begingroup\$ Is there are way of measuring voltage/resistance/current to tell what is ground here? \$\endgroup\$
    – Joel
    Commented Apr 12, 2020 at 7:32
  • 1
    \$\begingroup\$ Hej fellow Swede! Your lamp circuit is not grounded at all. It’s quite common at least in the 70s to route from your fuse central to the lamp post and from there to switches and outlets. Black is probably a different circuit for your outlets or possibly for your light switch. Flip the switch and measure again. \$\endgroup\$
    – winny
    Commented Apr 12, 2020 at 7:46

2 Answers 2

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Here is my guess:

3-wire lamps

The type of each cable can be easily determined using a voltage tester (neon lamp) and voltmeter as follows:

  • First find out the live wire(s) by touching it by the voltage tester.

  • Then connect the one probe of a voltmeter to the live wire and find out the neutral wire by connecting the other probe to wires. If there is voltage, the wire under test is the neutral wire (ground).

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  • \$\begingroup\$ The three wires are coming out of the ceiling where the light fitting was. It seems there is only one switch. \$\endgroup\$
    – Transistor
    Commented Apr 12, 2020 at 10:35
  • \$\begingroup\$ If the switch is only one, what is the need for a third wire? \$\endgroup\$
    – Circuit fantasist
    Commented Apr 12, 2020 at 11:13
  • \$\begingroup\$ That's the question! It could be one neutral and the live hopping off to the next lamp which is getting its neutral elsewhere or it could be one live and a neutral loop. \$\endgroup\$
    – Transistor
    Commented Apr 12, 2020 at 11:23
  • \$\begingroup\$ @Transistor Could also be live, neutral, and earth, no? \$\endgroup\$
    – Hearth
    Commented Apr 12, 2020 at 11:59
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The case is dangerous! Wrong connections or materials can cause dangers and invalidate insurances. Even electric works done by non-qualified persons can invalidate insurances.

There's no evidence are old wires connected as the code stated in the assembling day. More: You probably do not know the valid assembly day code.

Where I live the code has allowed as late as 20 years ago color variations if the wires were labeled. The labels can be taken off and as well the electrician can have decided "not enough that right color, but I use the other - who cares - time is money and other works wait!"

Do not make more unorthodox connections - get qualified local help or find the other ends of the wires!

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