Wiring problem, I think the CU has them wrong

[garethg]

I must admit I have not opened up the consumer unit, which would possibly answer this very quickly.

I have a lighting circuit, which only provides 3 lights (I hope) in an extension of a house, which was built around 10 years ago.

The three switches in this extension have been replaced with some electronic switches off-the-shelf. The lights are 60W standard lights, these are suitable for the switches.

I believe that the live and neutral in the CU have been swapped over.
I have attached a layout diagram of the three junction boxes which service the switches.

The junction box which is between switch 1, and switches 2,3 is wired, red to brown, black to blue.
The diagram has the following labels as inputs to the junction boxes:
I: Input cable
S: Cable to switch
L: Load (light)
O: Output cable to next switch
The first switch works as expected. The second two switches do not work correctly.

I believe:
1) The first switch is either actually switching the neutral on the load (I was taught this was a bad thing)
or:
2) The live and neutral on this circuit are reversed.

Is there any easy way I can tell this without opening the CU? (given the state of some of the things here, I wouldn't be surprised if a dead something fell out).
As switch 1 works, switches 2 and 3 don't I suspect 2 is the correct 'fault'

Thanks,
Gareth

 

[Taylortwocities]

You need
1. a test meter or voltage indicator (NOT a neon srewdriver)
2. someone who knows what they are doing

 

[garethg]

Test meter as in AVO? If the earth hasn't been connected (and as it is AC you can't test for positive and negative), there is nothing I can test against is there? Or do I just use a handy radiator as the earth/neutral lead (hoping that the infinite resistance of the AVO is infinite today)?
Gareth

 

[Taylortwocities]

I'm not going to discuss how electricity works. Its too late.
A test meter capable of indicating AC voltages is what is required. AVO is a trade name. A £5 meter from Maplin will do.


You really need item 2 from my list

 

[Spark123]

The earth should have been connected. If there was no earth available for the new circuit then the new circuit should not have been connected to it.
You don't have a system whereas the neutrals are run to the switch. Providing the L&N are the correct way around, in the top JB the black to the switch wire is permanent live, the red is switch live. This black should also have a red sleeve on it to signify it is being used as a line conductor.

 

[garethg]

Thanks spark,
I thought the earth was connected when I replaced the switch, the earth was wired in the back-box, so I wired it in. When things started going wrong was when I investigated further to find that it wasn't connected the other end (on the diags I didn't make it clear, the top JB has no earth wiring, the bottom two are wired, green on the diag). I suppose I should have checked when I wired it in, however the JB was in the ceiling, and there was no way of getting to it without either removing a radiator, or smashing a hole in the ceiling. I have learnt now not to trust other people's work.
There was no coloured sleeving to indicate that the black wire on the previous switch was live, it was also wired to the L1 terminal (which is where I prefer to think of things as 'neutral', as if the switch is in 'off', that is the safe(r) end, very simplisticly).

If the top JB is correct, then the electronic switch (1) is getting 'live' on its 'load' and load on its live.
The second two are getting 'live' on 'live'.

The first one works correctly, the second two don't, which is what is making me think that the L&N are swapped.
Gareth

 

[ban-all-sheds]

the JB was in the ceiling, and there was no way of getting to it without either removing a radiator, or smashing a hole in the ceiling. I have learnt now not to trust other people's work.

You've also learned why JBs should be accessible..

There was no coloured sleeving to indicate that the black wire on the previous switch was live, it was also wired to the L1 terminal (which is where I prefer to think of things as 'neutral', as if the switch is in 'off', that is the safe(r) end, very simplisticly).

You really need to spend time learning the basics of circuits, and current flow, and the difference between live & neutral etc.

If the top JB is correct, then the electronic switch (1) is getting 'live' on its 'load' and load on its live.
The second two are getting 'live' on 'live'.

So? As you pointed out, this is AC, and the phase voltage wo neutral varies from +325V to -325V 50 times a second, and current flow reverses direction.

The first one works correctly, the second two don't, which is what is making me think that the L&N are swapped.

What are these "electronic switches", and what does 'don't work correctly' mean?

 

[garethg]

You've also learned why JBs should be accessible..
---
What are these "electronic switches", and what does 'don't work correctly' mean?

Yup!

These are switches from www.homeeasy.eu.
Basic internals of the switches as far as I can determine are a step-down transformer, diode rectifiers, RF receiver, and electronic variac

Don't work properly has two stages.
1) the things get warm, this is what I am concerned about, only switches in this position, on this circuit, none of the others in the house.
2) not so worried about, this is the only position on this circuit where the switches default to 'ON 100%' when voltage is applied in circuit.

When in other places in the house, these switches do not do this,

Edit:
Perhaps a better way of solving/putting this is:
Is either of junction 2 or 3 incorrect (I don't think so)? The diagrams on the right are as wired.

Is junction 1 possibly better off wired with the switch cable the other way around, /plus/ better marking on the cables in the switch box?

 

[ban-all-sheds]

Better marking is definitely a good idea.

You need to check the switch documentation to see if it matters if supply and load are reversed, but I can't see how swapping it at switch 1 will affect switches 2 & 3.

You can check polarity quite easily with a multimeter - if the cpc isn't properly connected then you can (and should) fix that. You need to check polarity this way because assuming it in lighting circuits on the basis of colours is going to go wrong. And why "red live, blue neutral" anyway? The pairings are either red & black or brown & blue..

 

[garethg]

Thanks for the reply, unfortunately apart from wording 'take note of how the old switch was connected' and obvious markings of 'live' and 'load' on the switch itself, it doesn't explicitly state the correct way. The swaping the switch cable comment was basically, do most people expect red (brown) to be live at the switch (and I guess the answer is, those people with experience don't expect it to be anything )?

The JB is difficult to get to unfortunately, but I will give it a shot at connecting the earths (unless 'leccys mutate and grow special angular arms... ). If I don't immediately get a good earth connection, then I will call in an electrician instead (even if I do, will get them to double-check before covers go back on). Unfortunately it looks like whoever put this in, deliberately cut off the earth wires on the 4 cables in that JB.

And why "red live, blue neutral" anyway? The pairings are either red & black or brown & blue..

The way I drew the diagram, I thought that blue would be easier to see than black wires on a black 'outside box' that is all.

Luckilly, as this is meerly a hall light and outside light, it is not an urgent situation.

 

[ban-all-sheds]

Thanks for the reply, unfortunately apart from wording 'take note of how the old switch was connected' and obvious markings of 'live' and 'load' on the switch itself, it doesn't explicitly state the correct way.

If it labels the terminals that way then connect them that way. I wonder how electronics modules work with no power? - There's nothing at the switch with a potential difference. Do they never fully turn off, i.e. there's always a few mA flowing through the lamp to keep the switch powered?

The swaping the switch cable comment was basically, do most people expect red (brown) to be live at the switch (and I guess the answer is, those people with experience don't expect it to be anything )?

Most people who've never looked into it would expect red/brown to be live. They would also expect black/blue to be neutral, which causes no end of fun with traditional loop-in ceiling roses...

Unfortunately it looks like whoever put this in, deliberately cut off the earth wires on the 4 cables in that JB.

The unpalatable fact you now have to deal with is that the sort of idiot who would do that can't be trusted not to have done idiotic things elsewhere, so you need your entire installation checked...

The way I drew the diagram, I thought that blue would be easier to see than black wires on a black 'outside box' that is all.

Fairy nuff.

 

[garethg]

If it labels the terminals that way then connect them that way. I wonder how electronics modules work with no power? - There's nothing at the switch with a potential difference. Do they never fully turn off, i.e. there's always a few mA flowing through the lamp to keep the switch powered?

The switches have a blue LED on them, so certainly there is some power draw (and a DC requirement).
From what I can remember (from a long time ago), if you have a capacitor on an AC feed, with an infinite resistance behind it, you can get a little 'free' power from it (well, you cannot create energy obviously, but the 'neutral' is not required for power to accumulate in the capacitor). I don't think mains is enough to get any decent current though.

Just checked, by unplugging a lamp the LED on the switch immediately goes out, so there can't be anything magic like the above going on, there must be a small current flowing.
I suppose, if I could be bothered, I could measure the resistance of the lamp, the voltage either side, and determine what the resitance of the switch is. However, that will have to wait until tomorrow if I can be bothered.