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.

 

[Leesparkykent]

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.

Struggling to make sense of it at a quick read but what was the earthing arrangement?

 

[sparky1508]

TN-C-S. CPC at ceiling sleeved black and connected to neutral. 2 black conductors at switch have earth continuity without the CPC at light being disconnected. This tells me there is a CPC neutral crossover somewhere else in the circuit.

 

[sparky1508]

I will attempt to draw a diagram when I get home and post.

 

[Leesparkykent]

TN-C-S. CPC at ceiling sleeved black and connected to neutral. 2 black conductors at switch have earth continuity without the CPC at light being connected. This tells me there is a CPC neutral crossover somewhere else in the circuit.

was the main switch off?

 

[sparky1508]

was the main switch off?

Yes main switch off.

 

[westward10]

That sounds like fun, not clear why cpc is being used as neutral, seen it sleeved red and used as a line conductor. This is irrelevant but is it black sleeving or a bit of insulation from a black wire, you rarely see black sleeving.

 

[sparky1508]

That sounds like fun, not clear why cpc is being used as neutral, seen it sleeved red and used as a line conductor. This is irrelevant but is it black sleeving or a bit of insulation from a black wire, you rarely see black sleeving.

It is insulation from a black wire but it has earth continuity unless it is used as neutral and the CPC neutral fault I have is causing it to have continuity. Have done R1 R2 and get continuity.

 

[westward10]

The only thing that springs to mind is that there is a broken neutral conductor and someone has resolved it by using the cpc.

 

[sparky1508]

The only thing that springs to mind is that there is a broken neutral conductor and someone has resolved it by using the cpc.

Possibly I suppose but isn't that bad? Failed IR tests for a start and the possible risk of shock increases massively

 

[westward10]

It is bad but you see all sorts. What I would do is reconnect the cpcs sleeved black from neutral back to earth, leave them sleeved black so you know which ones they were. Then redo the IR test and see if it clears the fault. If it does I would then get a long wander lead and do continuity tests from the CU neutral to all points in the circuit to see if the neutral is okay.

 

[sparky1508]

It is bad but you see all sorts. What I would do is reconnect the cpcs sleeved black from neutral back to earth, leave them sleeved black so you know which ones they were. Then redo the IR test and see if it clears the fault. If it does I would then get a long wander lead and do continuity tests from the CU neutral to all points in the circuit to see if the neutral is okay.

I did the IR test with all conductors disconnected at the switch and ceiling and still failed.

 

[sparky1508]

It is bad but you see all sorts. What I would do is reconnect the cpcs sleeved black from neutral back to earth, leave them sleeved black so you know which ones they were. Then redo the IR test and see if it clears the fault. If it does I would then get a long wander lead and do continuity tests from the CU neutral to all points in the circuit to see if the neutral is okay.

Is there an increased risk of shock from exposed conductive parts?

 

[westward10]

I would say yes and no. You have a TN earthing system so neutral and earth are deemed as being at the same potential. The danger is where the cpcs are being used for an alternate purpose, are there parts of the circuit which are now without an earth. Also if there is a break in the neutral and the cpcs have been used to resolve this then the cpcs at some point, if disconnected may have mains voltage present.

 

[sparky1508]

I would say yes and no. You have a TN earthing system so neutral and earth are deemed as being at the same potential. The danger is where the cpcs are being used for an alternate purpose, are there parts of the circuit which are now without an earth. Also if there is a break in the neutral and the cpcs have been used to resolve this then the cpcs at some point, if disconnected may have mains voltage present.

That is my thinking and back to the MET and mains voltage on all circuit CPCs. Is that possible.