UK - low voltage from mains cable?

Question

I've lived in this house for a couple of years now and I'm in the process of mounting a pair of Sonos One speakers in the corners of my kitchen.

I was working on the premise that I would need to run some cables down the wall to a wall socket, but when I got up to look on top of the cupboard there were two power cables coming from the wall (each cable with L/N/E) going into a inline connector box (similar to https://www.screwfix.com/p/debox-in-line-connector-box/8692h) - Result I thought ...

I bought a new dual socket outlet, and prepared to wire it up. After doing so and plugging in the Sonos ... no dice.

Hooking up a multimeter to the cables I'm getting 180V Live to Neutral, and 180V Live to Earth. I believe I should be getting 240V from a UK mains connection unless I'm mistaken?

I did some more testing, and removed the cables from the socket to rule that out, and it looks like only one of the cables is actually live - the other 'live' cable doesn't give me any voltage at all.

Do I need both to get to 240V or is there something else at play here?

Answer 1

There are many applications in home wiring where part of a circuit requires 2 wires travel somewhere. However, as it works out, they are not hot and neutral - they are whatever and whatever - switched-hot and travelers, hot and switched-hot for a switch loop, you name it. You as an electrician are expected to know of the existence of such arrangements. They don't make special cables for these. You use the exact same commodity off-the-shelf brown/blue T&E that you use for everything else. And you, as an electrician, are expected to recognize one of these odd arrangements when you stumble upon it.

If you really want to iterate on this question, you can keep following wires and testing, and you will eventually discover what this box is associated with and what it does. However that is orthogonal to your goal, and I strongly recommend against trying to learn electrical by tinkering; this results in a very "holey" education (as does searching Google). Books provide a far more complete education far more efficiently.

Answer 2

The single phase supply voltage in the UK is 230V a.c -6% to +10%.

In the UK 180V is not a voltage you will ever see. Either your meter is faulty, you are not using it correctly as in reading d.c voltage instead of a.c voltage, or you have what is called a floating neutral which is a wiring fault and possibly a neutral has disconnected somewhere in the circuit.

Regardless this is not something you should be playing around with. As well as possibly being electrocuted which includes the risk of death you also risk creating a serious fire hazard. You do not know what this circuits intended purpose is. In a kitchen at that height it could be a lighting circuit for example. These circuits use in older times 1.0mm T&E which is not suitable for carrying socket loads. It may even be an abandoned circuit for the reason you have even mentioned. Unlikely however and certainly not safe in that condition but historically all sorts of quirks happen.

I would point out that all electrical workings in the UK are notifiable to (Part P of the Building Regulations) meaning you need to be an electrician to do them. Quite frankly Electrical is not something anyone should be doing as DIY as it is too dangerous and people get it so wrong all the time. Half my career is made up fixing their mistakes.