Fault finding - insulation testing

[Sparky_marky2]

Hi everyone, did some insulation testing on my mates house as his RCD was tripping manage to isolate it to the ring circuit, Live-Earth for the ring circuit came to 0.01Mohms and all appliances have been disconnected and removed.

However I have disconnected the Live-Earth behind one socket (Socket A) in order to split the circuit and with the process of elimination work out and get closer to where the fault is.
I got readings of >900 for another socket in the same room (Socket B) but when i reconnected the Live-Earth in that Socket A and tested Socket B again just to make sure the reading fell to 0.03Mohms.

Theres no clear correlation to which sockets are ok and which aren't for instance there are four double sockets in the living room all will have a reading of 0.03Mohms but one will be >450Mohms and the dining room next door also has 4 double sockets and two have given a low reading of 0.02Mohms and the other two have >550Mohms, any ideas?

Thanks in advance.

Mark

 

[Bob Geldoff1234]

It sounds like you have got joint boxes under the floor feeding various different sockets.If you cannot break the ring to find the fault then usually i would remove all the sockets and using a trailing lead test between each pair of wires to determine where they go.Draw a diagram of the rooms and overlay the schematic of where each wire goes.Only then can you make sense of how it's been wired,how many joint boxes there are and ultimately where the fault is.

It sounds like damp from your readings.Could be in a joint box under a wet floor or in the back of a socket on a damp wall.
Good luck finding it!

 

[Octopus]

I can't quite make out what you are doing tbh .... Have to checked the continuity of the ring and tried to determine which are Spurs?

Sound to me as if you could have an old ring, with junction boxes under the floor and Spurs off Spurs .....

Had something very similar earlier this year .... Different ages and types of cable too

 

[Sparky_marky2]

It sounds like you have got joint boxes under the floor feeding various different sockets.If you cannot break the ring to find the fault then usually i would remove all the sockets and using a trailing lead test between each pair of wires to determine where they go.Draw a diagram of the rooms and overlay the schematic of where each wire goes.Only then can you make sense of how it's been wired,how many joint boxes there are and ultimately where the fault is.

It sounds like damp from your readings.Could be in a joint box under a wet floor or in the back of a socket on a damp wall.
Good luck finding it!

I'm going back tomorrow evening to have another try this time disconnecting all Live-Earth conductors from behind the sockets and doing individual IR tests along each hopefully to find the problem. I had thought about joint boxes under the floors, my mate bought the house of a guy who had bought it to 'refurb and sell on job' and he doesn't have any testing certificates for me to go off.
Yes I've already prepared a diagram ready for tomorrow, I hope it isn't damp...... It has been chucking it down the past few days!

 

[DPG]

Let us know what you find !

 

[Lucien Nunes]

Don't start with IR tests. Do as mentioned above and use continuity tests e.g. on the N conductor, to trace the wiring. Then, the IR tests you do will be much more meaningful as you know which parts of the cabling they will reach.

An L-E of 0.01MΩ is very low even for a damp fitting, but you aren't getting much useful info from using the IR range bottomed out like that with just one digit reading, it could be one ohm or ten thousand, so you don't know what kind of problem to look for. Test the IR with your DMM or 250V or continuity range and see just what it is like. If it reads say 10Ω you know it is an intermittent short that will probably be scorched and smell of burnt stuff. If it's 15,000 ohms then it might just be damp.

 

[sparkdog]

Might be a mouse has made a meal of the insulation.