Odd one

[SPECIAL LOCATION]

If you take the cables out of the consumer unit while all others are connected and test between L and E with the ends separate it reads 50Mohm. Which while not good is a pass.

Join Ring L1 to Ring L2 and Ring E1 to Ring E2 and then test between L & E you get 0.03Mohm.

This doesn't even follow the 1/4 measurement when doing a crossed r1+r2 test.

Can't see anywhere that you have told us what your actual continuity readings are around each leg..
(or r1+r2 test values?)

and not sure how you are equating insulation resistance values to 1/4 measurements doing crossed r1+r2s?

 

[mort2376]

The continuity isn't important. The readings are correct end to end.

And r1+r2 readings are correct when cross connected. But that does not affect the Ir readings I'm getting

 

[binky]

Even with the break at a socket not at the CU 40Mohm v 0.03Mohm.

Don't see how that is possible , unless you have 2 breaks in the ring.

 

[mort2376]

That's what's driving me nuts about it. It makes no sense.

I'm sure I'll be back there in the near future and hopefully I'll get my answer.

 

[SPECIAL LOCATION]

No one has yet managed to answer why the reading is different open ring and closed ring.

I have given an example based on info from your earlier posts of how a live conductor with insulation damaged making contact with a nail or metal capping, metal studwork or other non-electrical metal parts fixed to the fabric of the building would cause different readings to E depending upon which parts are open/closed, and/or connected at CU or not...

And as UNG mentioned nails touching but not piercing a cable conductor... Picture hook, dado rail fixing, Christmas decoration hanging point... etc.. etc.. .can cause all sorts of weird readings..

As you haven't provided a comprehensive list of test results around the whole circuit..
Including continuity measurements at every outlet point and IR's for each section of cable..
anything else is just a bit of guesswork.

Personally with these sort of problems I find you can get yourself tied up in knots forgetting exactly what you have or haven't tested...

Normally I find it best to get back to basics and identify exactly how the circuit is wired...
Then start from the CU down one leg of the ring measuring and noting everything on an A4 pad..
Room / Socket / L to E and N to E continuity's check they match / IR between everything L-N, L-E, N-E..
etc.. etc.. around every outlet on the circuit that you can find..

Then as you work your way around the ring something normally crops up as clearly incorrect and points you to the cause of your dodgy reading(s)...

Some I have found have clearly been there for years... but as no PIR's have been done..
And as everything was still "Working" the customer was oblivious..

In your specific case where you have left it with the customer "seeing how it all goes" re further RCD tripping..

I would have ready a copy of Best Practice 4 recommendations...
And if you are called back say that you need a full days labour to do more comprehensive testing around the whole circuit..
During which time you may be able to resolve the problem..
Or it may need further labour and materials to resolve based upon what your further testing reveals..?

During these sort of tests I get very meticulous with my measurements, especially continuity along ALL conductors making sure they are ALL proportional to the expected cable lengths.. [L-N, L-E & N-E],
As dodgy readings are often an indication of: Bad joints, Nails in cables, Squashed conductors.. Damp, Rodents influences etc..

Without further circuit detail info and more test readings, I think we are all second guessing this one?

Have you verified that there are NO crossed circuits / borrowed neutrals / shared earths??

e.g. I've seen a conservatory take its lights 'Live' from the from the lighting circuit..
but neutral from the sockets.. Cant remember where the Earth came from..?
But it caused a few testing head-scratching moments until it was tracked down!!!!

 

[UNG]

No one has yet managed to answer why the reading is different open ring and closed ring.

Without knowing or having any visual information on the layout of the faulty circuit it is difficult to pluck any answers out of thin air as to why you are getting the readings you are.
Also from the random and limited information and test results you have given it is difficult to build a picture of what other checks you have done during the time spent onsite that could be useful in finding an end result
I have had similar issues and have found that the test leads I was using had an intermittant minor fault that was affecting the accuracy of some of the readings I was getting so don't just assume the meter is correct

You appear to have a fault that is a bit more than basic faultfinding while some faults are extremely easy to find there are some that do try the patience and need a very methodical approach and analysis that needs a notepad to map out the circuit and the readings obtained at each point and from that it may become more obvious where the problem lies

I have had faults where people moving around in the property gave intermittant faults because cables where trapped by floorboards or had nails / screws that were just long enough to pierce the cable when the floorboard was walked on

I find a cable tracing tool to be a useful addition to the test kit as it makes it very easy to locate those live nails and screws that are potentially causing the problems also helps to map out a circuit and find hidden accessories

 

[binky]

Concur with @UNG , plus I think you've driven yourself to distraction, which is when logic tends to get lost and you just confuse yourself. If you do go back, I reckon you could find the fault or at least the faulty leg in under 2 hours. And, yes, I have done this myself

 

[mort2376]

Yeah I was thinking that. I've been there before when your head gets tied up on an issue.

I've messaged the customer so waiting to hear back.

Thanks peeps

 

[sirsparkabit]

I also find if I can't find a fault within 2 hours ,or one that's taxing my brain it's always a good idea to walk away from it, sit down or do something else for a while then take a reasoned methodical fresh approach . Ung is quite right draw it out on paper and record results of tests ect .
I had a Brian Scadden book on fault finding years ago which with maths could pinpoint some faults within a half metre or so , found that very handy.

 

[Mike P]

Concur with @UNG , plus I think you've driven yourself to distraction, which is when logic tends to get lost and you just confuse yourself. If you do go back, I reckon you could find the fault or at least the faulty leg in under 2 hours. And, yes, I have done this myself

I find it good to put a difficult fault aside (unless dangerous), re group and re think and go back With a fresh approach.

 

[Andy™]

I also find if I can't find a fault within 2 hours ,or one that's taxing my brain it's always a good idea to walk away from it, sit down or do something else for a while then take a reasoned methodical fresh approach

done that many times, left it and gone back the next day and sorted in almost no time

 

[UNG]

There are times the phone a mate / friend option (assuming you have a mate / friend who is an electrician) can give you a useful sanity check and offer some other ideas when fault blindness sets in

 

[kerching]

I have a couple of TDRs ( Time Domain Reflectometers ) that get dusted off from their me to time
One is a JDSU Acterna as used by Telecom Companies, this will pinpoint a fault to,within 0.5 m over about 3km.
Brilliant for data and telecom faults
Other is a BICCOTEST Faultman, same principle but has a filter so you can fault on a live cable
But in both cases it tells you distance to fault so you have to know the cable run. This is a challenge on a golf course irrigation system but I've not been beaten yet

 

[Sharpend]

I have a couple of TDRs ( Time Domain Reflectometers ) that get dusted off from their me to time
One is a JDSU Acterna as used by Telecom Companies, this will pinpoint a fault to,within 0.5 m over about 3km.
Brilliant for data and telecom faults
Other is a BICCOTEST Faultman, same principle but has a filter so you can fault on a live cable
But in both cases it tells you distance to fault so you have to know the cable run. This is a challenge on a golf course irrigation system but I've not been beaten yet

Why am I not surprised that you have a tool for every job!

 

[kerching]

Why am I not surprised that you have a tool for every job!

Actually TWO for every job.......good to have a spare

Winds our kids up,when I tell them that "one day all this will have to be sorted out by you three"

 

[Sharpend]

Actually TWO for every job.......good to have a spare

Winds our kids up,when I tell them that "one day all this will have to be sorted out by you three"

Ouch that’s going to hurt, especially if you’ve only got two of each! You will be cussed.

 

[Andy™]

puts my single TDR to shame then. it doesn't have a sibling, it just sits there all on its own (although it does have a thermal camera & hydraulic crimpers as neighbours)

 

[kerching]

Mmm hydraulic crimpers, I've only got 4. I think 500mm'2 is the biggest
So at least they can have one each and wife can have one as well. I'm nothing if not fair

 

[kerching]

Cancel that. It's FIVE crimpers. Forgot the foot pump one that at present has the shears on it

 

[Andy™]

only 1... and its a mere 300mm capacity