Fault on Ring final circuit

[westward10]

Agreed as that is what an IR test is doing, testing for any continuity between L-E, N-E.

Just trying to say End to End continuity tests don't help too much in this scenario.

Totally agree and when I get a "flat" IR I immediately switch to continuity.

 

[DefyG]

The rn may be lower due to a fault to the cpc.

It could but not as conclusive as an IR test.

 

[AJB Temple]

I will do an IR test. That is helpful.

My amateur logic suggested that CPC was unlikely to be at fault as the resistance r2 was as expected vs rn.

It now transpires that although the CU has upstairs sockets on a different RCD to downstairs sockets according to the labels, the reality is that some upstairs sockets at one end of the house are out of action as well. CU clearly not labelled correctly. I think that the socket which started all this off, goes directly up to that area and it seems very likely to me that I will have to excavate that wire from the wall and conduit

 

[littlespark]

Cables don’t generally break down for no reason… so the most likely issue is with a connection in the back of a socket, OR recent works have damaged a cable… any new things been screwed to the wall above a socket?

In the OP, it suggests that the circuit has been moved between mcbs and onto the other side rcd…
You may have left a neutral on the wrong N bar,
Each rcd supplies a bank of mcbs AND the corresponding neutral bar

You do say it’s a bit of a mess and you may have missed it.

 

[AJB Temple]

Thanks liitlespark. Yes, I did move the entire ring across the CU to a different RCD to help eliminate RCD and MCB issues. I moved all six ends. It just tripped that RCD so very unlikely to be an RCD or MCB issue I felt. I had a spare 32A MCB on that side that I knew worked. All six ends are now disconnected from the CU so that I can have everything else powered up. I am very clear about which wires are on each side of the defective ring inside the CU. I am not a domestic electrician so I spend a lot of time double checking everything, including proving dead every time I do anything (I am working on my own).

Yes, studwork was put up in the room where the fault first emerged. I have added 150mm to 200mm internal insulation and panelling to the whole core of the house. The stud was actually fixed to an adjacent wall but tomorrow I will remove the panelling in the area and check that there has been no screw or nail gun penetration into the conduit. It's unlikely (I did all the studwork) and it is 200mm away from where the conduit is buried in the wall. However, I will check it in daylight. Thank you.

 

[AJB Temple]

You had me worried there so I just went and removed the panel in that section of wall (which luckily was not glued to the stud - 2nd sight saved me). However, there are no nail or screw penetrations into the wall where the conduit is buried. But I can't help thinking the problem lies somewhere in that section of cable.

 

[westward10]

Do an insulation resistance test.

 

[mainline]

You had me worried there so I just went and removed the panel in that section of wall (which luckily was not glued to the stud - 2nd sight saved me). However, there are no nail or screw penetrations into the wall where the conduit is buried. But I can't help thinking the problem lies somewhere in that section of cable.

Only testing will tell for certain.

Some like to think and some like to do, the ones that do both are the ones who fix it.

 

[AJB Temple]

I will definitely fix it. But please remember I am an amateur at DIY electrics and to a degree have to learn (courtesy of YT vids from GSH etc) as I go along. Hence it takes me ages to do what you guys would regard as obvious.

Naturally I want it all to be safe. Obviously I will get my electrician to check it when he gets back in February.

 

[AJB Temple]

OK. Here is what is happening to me. I have disconnected all six ends from the CU as I don't want to test the whole board, just this one circuit. Neon bulbed spur is switched off (this feeds an outside socket). Nothing is plugged into any socket as far as I can tell. (Do I need to worry about switch positions on the sockets?)

MFT1711 has green and red leads plugged into same colour sockets, leads checked for OK and zeroed. Left dial set to 500v in the red zone. Right dial is on 30 in the yellow (but doesn't matter?) "Air test" shows 999 as expected. Tested together and I get a 0 (dead short) as expected so test leads OK and meter working.

Dividing the ring circuit into Left and Right I get:

Left side
L-N 0.00 M ohms
L-CPC 0.15
N-CPC 0.15
L+N-CPC 0.14

Right side
L-N 0.00
L-CPC 0.17
N-CPC 0.15
L+N -CPC 0.15

This suggests to me that I have a dead short on the live side somewhere? Is that correct? Even though L-L continuity seems to be OK as testing at o.81 ohms today.