Dodgy wiring

[sparky1508]

Hi all,

Changed some standard pendant lights today and the wiring was a bit dodgy.

The first light I looked at had 3 red ( normal ) 1 switch line ( normal ) but 3 neutral and 2 cpc. One I the cpc was sheathed in black and connected in the neutral of the light a continuity check confirmed it was connected to earth.
Second thing the light is on 2 way switching and in the first switch was 3 reds connected together 1 of which was from 3 core and cpc which went to the common of the second switch. 2 strappers yellow and blue in the correct place. There is 2 blacks in the first switch connected together and I disconnected them and checked and one was continuous with earth so when connected they both are. I disconnected the whole lot in the switch and ceiling rose and ran an IR test. L - N >500 Mohm
L - E >500Mohm
N - E failed.
Can anyone shed some light on this or is this a danger. My thoughts are that the earth in the light fitting shout not be connected to the neutral at any time and also is this likely to liven up anything connected to earth. His circuit is not on the RCD either.

 

[7029 dave]

Here you go. What's the answer.
View attachment 32885View attachment 32886

Looking at the first pic, to me it looks like that is the S/L cable and somebody has used the cpc as a neutral down to the switch position.

 

[sparky1508]

Looking at the first pic, to me it looks like that is the S/L cable and somebody has used the cpc as a neutral down to the switch position.

That was my first thought but on doing R1/R2 it turns out that the cpc sleeved black is actually connected back to earth and so are the 2 actual neutrals in switch 1. They were still connected to earth with the entire 9 conductors separated at the ceiling so it tells me neutral and cpc are interconnected elsewhere.

 

[7029 dave]

That was my first thought but on doing R1/R2 it turns out that the cpc sleeved black is actually connected back to earth and so are the 2 actual neutrals in switch 1. They were still connected to earth with the entire 9 conductors separated at the ceiling so it tells me neutral and cpc are interconnected elsewhere.

So we know the switch line cable cpc is connected to N on the ceiling position where is it connected at the switch.?

 

[westward10]

Try not to rip this circuit apart you will get more confused. Break it down methodically and if necessary draw a plan to see if you can narrow the problem down.

 

[sparky1508]

So we know the switch line cable cpc is connected to N on the ceiling position where is it connected at the switch.?

Sleeved black again and connected to neutral which is also connected to earth. No idea where that neutral goes after that without starting to take the circuit apart. Customer can't afford to pay for full investigation as the job was only supposed to be changing the pendants as they are moving house and wanted to take other fittings with them.

 

[7029 dave]

I would say at a guess, that cpc is connected at the switch position to earth hence your NE interconnection, just take the switch plate off and look.

 

[westward10]

I know this is a bit late but for future reference always test the circuit before undertaking any works on it so this issue doesn't arise again.

 

[andyb]

That was my first thought but on doing R1/R2 it turns out that the cpc sleeved black is actually connected back to earth and so are the 2 actual neutrals in switch 1. They were still connected to earth with the entire 9 conductors separated at the ceiling so it tells me neutral and cpc are interconnected elsewhere.

Did you disconnect the neutral of this circuit at the board before testing?

 

[sparky1508]

I would say at a guess, that cpc is connected at the switch position to earth hence your NE interconnection, just take the switch plate off and look.

Done that, one of the 2 blacks at the switch is cpc sleeved with insulation from black conductor the other one is an actual neutral but it has continuity with earth even with all conductors at the ceiling separated. This is what make me think the interconnection is elsewhere in the circuit. I would need to dismantle the circuit bit by bit and do continuity on each section to find what's going on but like I said, I have spoken to the customer about the problem but they haven't got the budget to pay for and investigation that would probably take a whole day. I have told them of the risks and changed all light fitting to the standard plastic ones now so minimal risk but still a risk in my eyes.

 

[7029 dave]

Well going by your drawing it's 3plate and if it's been wired like that at every ceiling position, the interconnection will be at every point? you have trouble, you need to drop every rose and look. It can't be left.

 

[andyb]

Shouldn't take too long. It looks like someone has taken a live and neutral from the switch, as there was no neutral there they used the cpc of the switch wire. Disconnect the live and neutral coming away from the switch, not the 3 core or the switch wire, and see what doesn't work. Should tell you what's happened.

 

[sparky1508]

Did you disconnect the neutral of this circuit at the board before testing?

Disconnected all 3 conductors for testing once I saw how it was wired at the first lampholder. That's how I figured it had neutral earth connection as IR test failed on neutral to cpc.

 

[sparky1508]

Well going by your drawing it's 3plate and if it's been wired like that at every ceiling position, the interconnection will be at every point? you have trouble, you need to drop every rose and look. It can't be left.

It's not like that at every point. The first one in the toilet is fine, the second in the hall just has stranded 3 core flex coming out of a hole then there's this one in the living room, then a dining room and kitchen which are both wired standard 3 plate so this is the only one I have issues with.

 

[telectrix]

came across something like this some years ago. what had happened was that an outside light had been wired from the hall light switch and the guy who did it realised there was no N at the switch so he used the cpc of the switch drop, connected it to N in the rose to get a N at the switch.

 

[gazdkw82]

Id start by drawing a proper wiring diagram going from light to light and then work out what's going where. If you can narrow down which is the feed from the previous rose and which is the feed to the rose it means you only have to figure out what's going on between the rose in question and the switch.

Thay being said, if all cieling roses are like this one you have your work cut out