I am trying to determine if my light switches have a neutral wire, as I need to know if I can order smart switches with neutral wiring required.

Here in this picture you can see two example outlets:

  1. Blue and brown wire connected, green/yellow wire not connected
  2. Blue, brown, green/yellow wires all connected light switches

I have tested the first outlet with a multimeter and a voltmeter pen. The voltmeter pen lights up at the brown and green/yellow (albeit much less on it) wires. Connecting the blue and brown wires also gives 240 V as it should.

Furthermore, I am in EU, so I understand it is standard to have green/yellow be ground, and blue be neutral.

Lastly, at a different socket, I tested the same things and all was the same except green/yellow did not make the voltage pen light up at all.

My questions are as follows:

  1. Can I be assured that green/yellow is ground and blue neutral?
  2. Are the light switches wired okay? Someone on a different subreddit told me neutral should never be wired to a "dumb" light switch, but if blue is neutral, then it doesn't make sense.
  3. Is it normal that on one outlet I get some voltage on the green/yellow wire? Would this be an issue if I want to use that (assuming it is ground) wire in the future?

Thank you in advance!

  • are these outlets or switches? You ask about smart switches, but seem to show outlets. All outlets will have a neutral, as will newer switches. Please clarify.
    – dandavis
    Oct 11, 2023 at 21:52
  • Outlets and light bulbs need to have neutral, switches should only switch hot/live. Not sure how Europe does it, but US switches used to be able to use a white(your blue) as hot in a switch loop. Power goes to light box with a brown/blue cable to the switch, blue carried power and brown became switched hot. If it is an outlet, then blue is neutral(unless your wiring is really messed up), only switches you need to be careful, neutral does not connect to switch(in US).
    – crip659
    Oct 11, 2023 at 21:53
  • @dandavis sorry, english isn't my first language. these are the holes that are between the dumb light switches (which I took down to check the cables behind them)
    – Dani
    Oct 11, 2023 at 21:59
  • Where are you from... believe it or not but different countries have different conventions.
    – Questor
    Oct 11, 2023 at 23:34
  • Will need to check European electric, but US ground is bonded with neutral at the main panel. So you would read local(yours ~230) voltage between hot and neutral and hot to ground. Neutral to ground should be 0 volts. Ground is just there for your safety. It only provides a path for current to escape from going though you.
    – crip659
    Oct 11, 2023 at 23:34

1 Answer 1


You (almost certainly) don't have a neutral wire in those boxes. While blue is the standard colour for neutral, in switch boxes it is commonly re-used for 'switched live'. This is because while twin-brown cable does exist to be used in this situation, most people either don't know about it or don't want to buy 2 different types of cable. Switched lives should have brown tape or sleeving applied, but this is generally only done by the most conscientious electricians.

To answer your questions specifically:

1a. Green/Yellow is almost certainly ground (earth). It should never be anything else.

1b. Blue is almost certainly NOT neutral here

  1. Yes, your switches are wired OK. The blue wires are switched lives, not neutrals

  2. It's not uncommon for a voltage pen to light up on ground wires, it doesn't necessarily indicate a significant fault. Having said that to have it behave differently at different switches / sockets would indicate that the grounding is not continuous between those points which is a serious fault, because that would mean that at least one of those points is not correctly connected to the main earth point

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