Low Insulation resistance readings when connecting final socket on ring?

[Justintime]

Hello All wondering if anyone could shed some light on a problem i have with my IR readings.

I recently rewired a house.. took care pulling cables in etc . finished 1st fix, checked cables by looping ring main in connector blocks and doing continuity and IR test . continuity was ok, IR read >999. everything fine.

Few weeks later came back..

2nd fixed , mounted board , terminated , sockets on tested circuits , all tests were fine apart from my IR readings on the ring mains>?? readings between N/E conductors was around the 1.6Mohms. and L/N around 2.3mohms

Investigated, Disconnected main earth & neutral . split the ring in half, took socket off to see which side the problem was on and both halves were reading >999 on both legs & all conductors?? i thought that socket was the problem so i tested by replacing with connector blocks but once loop was complete the readings dropped right down again??

the sockets are hager.. so not too cheap i cant understand why this is happening, can anyone help

 

[Octopus]

Have you disconnected the lives and neutrals of the ring at the cu?

 

[Justintime]

Yes Murdoch i have

 

[Octopus]

Then you have no choice but to add the sockets one by one and testing ir after each one is added

 

[PEG]

Hello All wondering if anyone could shed some light on a problem i have with my IR readings.

I recently rewired a house.. took care pulling cables in etc . finished 1st fix, checked cables by looping ring main in connector blocks and doing continuity and IR test . continuity was ok, IR read >999. everything fine.

Few weeks later came back..

2nd fixed , mounted board , terminated , sockets on tested circuits , all tests were fine apart from my IR readings on the ring mains>?? readings between N/E conductors was around the 1.6Mohms. and L/N around 2.3mohms

Investigated, Disconnected main earth & neutral . split the ring in half, took socket off to see which side the problem was on and both halves were reading >999 on both legs & all conductors?? i thought that socket was the problem so i tested by replacing with connector blocks but once loop was complete the readings dropped right down again??

the sockets are hager.. so not too cheap i cant understand why this is happening, can anyone help

I would do this test from both ends of your "halves",that is,a set of tests on the two ends at the socket,and a set at the two ends CU end.

What results have you for continuity of the three conductors on that circuit?

Do not discount one wayward screw,causing more than one type of fault,on one conductor.

 

[Baker1988]

Seems to me like maby a nail gone through the cable somewhere, When you have split the ring and tested and got >999 Mohms are you sure you did not mix the cables up as you could of been testing the L from one leg to the N of the other leg and as you split the circuit you would basically be testing between 2 separate circuits, then when you re-terminated into the socket you was testing the ring as a whole which was bringing the fault back to light. Just a thought.

 

[ferg]

Sometimes if you are getting low IR readings that disappear when you reterminate there is damage to the insulation within a couple of inches of the point you are working on.

Moving it about can clear the fault.

Only for it to reappear once the new socket is put back in place.

 

[Justintime]

Yeah M8 ended up taking all the sockets off , IR tested every cable double checked legs aswel all above >500 thought fault had cleared so put sockets back on test result this time was 18.3Mohm , so took sockets off again lol replaced with connector blocks checked again , all conductors >500!! replaced sockets 1by1 first socket i put on insulation resistance dropped <500 .. WTabsoulteF Ive left sockets off to hopefully dry out abit (if there was damp?) otherwise not sure what else i can do

 

[Justintime]

Seems to me like maby a nail gone through the cable somewhere, When you have split the ring and tested and got >999 Mohms are you sure you did not mix the cables up as you could of been testing the L from one leg to the N of the other leg and as you split the circuit you would basically be testing between 2 separate circuits, then when you re-terminated into the socket you was testing the ring as a whole which was bringing the fault back to light. Just a thought.

yes, i know what you mean..

 

[Justintime]

I would do this test from both ends of your "halves",that is,a set of tests on the two ends at the socket,and a set at the two ends CU end.

What results have you for continuity of the three conductors on that circuit?

Do not discount one wayward screw,causing more than one type of fault,on one conductor.

think the continuity was .89ohms L&N earth around 1.38

 

[David M]

Yeah M8 ended up taking all the sockets off , IR tested every cable double checked legs aswel all above >500 thought fault had cleared so put sockets back on test result this time was 18.3Mohm , so took sockets off again lol replaced with connector blocks checked again , all conductors >500!! replaced sockets 1by1 first socket i put on insulation resistance dropped <500 .. WTabsoulteF Ive left sockets off to hopefully dry out abit (if there was damp?) otherwise not sure what else i can do

Have you tested the sockets themselves? Has it been recently plastered? If all the conductors are testing out ok then its a good bet that the sockets themselves are damp. I'd test them to see and if the IR is low then as you said let them dry out and test again. This way you can rule out a faulty batch of sockets, which is unlikely but possible.

 

[Doomed]

Slightly damaged inner sheath of conductor being pushed against metal back box when socket is screwed on, or the socket screw being pushed tight against the inner sheaths?

 

[HandySparks]

Box of sockets left outside in the rain before second fix?

 

[PEG]

...Without being there,it is all supposition...who knows,someone could have stuck a neon behind every S/O,to make them easy to find in the dark :mickey:

 

[Justintime]

Slightly damaged inner sheath of conductor being pushed against metal back box when socket is screwed on, or the socket screw being pushed tight against the inner sheaths?

Thanks. Will keep an eye on that