help and advice for IR on a Ring circuit

[brucelee]

HI all

I need some advice and guidance on a lower then expected IR on a New ring final circuit

when carrying out testing continuity was correct and so to the IR testing
I tested L-N >299 perfect
L-Cpc >299
N-Cpc > anywhere from 40M/ohms to 299

so as its new rewire I split in half at centre point and began trying to locate any damage trapped Neutrals in back box etc
as i was splitting and testing the reading began to rise
so i took all sockets of on the suspect side
all individual legs were 299
so started to reconnect 1 at a time conducting further Ir and as I got so far reading lowered
the readings are Fluctuating and if you hold the test button down readings rise
sometimes as low as 40+meg sometimes all the way upto to 299

I suspected new wet plaster or there is a socket in rear bedroom on rear wall and previously this wall had been damp or water damage due to plastic windows fitted in old wooden sash frames the wood has rotted so water had been penetrating and damaged the plaster on this wall when chasing all plaster on this wall under window fell off

anyway I cannot pinpoint the low reading to any individual socket or length of cable
as i suspected this socket and after trying locate for 5 hrs plus
thought wait for the plaster to dry as it was deep depth of plaster here
the plaster has now been done for over a week so should be dry
so tested again and still readings at ccu range from 40+ upto 299
I repeated half splitting method and still no joy when i disconnect neutrals and earths at sockets readings rise soon as i reconnect readings fall
without sockets screwed back

I know this may sound daft and dont know why i decided to try it but
I decided to test between the Neutral of the socket and the wall and got similar strange readings
so just meggered the wall lol and got very low reading of 0.05
the wall at the side 2 feet away i got 299

I then decided to check for any voltage present between sockets and any copper pipes under the boards nothing
I tested between line and the wall for voltage and got 131v??????

tested nearby wall from a High level TV socket on this wall and got 5v
tested the suspect socket and the nearby wall and got 5v

Do you think damage has occurred to cable from plaster or plumber
the wall maybe causing issues due to damp


any help on this would be truly grateful as its fried my head lol spent 10hrs in total trying to pin it down i even tried bypassing sockets with new lenght of cable from living room socket to rear bedroom

WISHING I HAD INSTALLED TWO RADIALS

ideas please

 

[Des 56]

Lower than expected readings that rise during the test may very well indicate that damp plaster was the cause
Having allowed the plaster to dry and taking into account the readings you have mentioned,both voltage and the low N-E insulation values
I would suggest you have a nail or such penetrating the cable in that location
Try using a voltstick along the wall and see if it picks anything up

I would have thought that the satisfactory readings you are getting when the cables are dis connected, is because the cpc is no longer making connection with the nailed neutral, because its removed from the back box,which is where the connection may be being made between the N-wall-cpc

 

[brucelee]

Cheers for the reply des

I have tried everything i can think off so will try the volt stick

the cable comes from under floorboards up 450mm to socket
when i got the 131v i thought gulp lol someone has hit it

its had me baffled just as i think i have pinned it down the readings are back up and leave me baffled lol
this is the mother in laws house and job for assesment so was trying to get everything perfect first and every time

the plumber with his wonky plastic and copper piping run all over shop including on my cables so had to move them myself and place on a brick or 2 to lift them away from cables and the plasterer have been in since me
this is last chance to sort I told them let me test it all before fitting flooring but they have gone ahead anyway
this leg of the cable goes from living room to the back bedroom its only 2 up 2 down terraced house

all back boxes are earthed also

 

[Des 56]

Another test you can carry out if you haven't already done so, with the cables disconnected from the socket fronts,
insulation test between the conductors and those metal back boxes
If there is cable penetration,you may be able to locate or narrow it down that way

 

[brucelee]

thank you des will try the methods you have described
my mrs brother works for a builder and he had there elecy come look which i wants impressed but remained calm he came up with same as me also said it could be due to plumbers solder or the fact that her brother gave me some skts and bits of cable he had from work or his shed

Most of the stuff came from neweys
but instead of getting all i asked for i have had it in bit and bats from different locations
its been a royal pain in the --- turning up to see if plastere been and finding out he has not most rooms are done except this back bedroom and the kitchen
they are away from saturday and this is when these rooms will be finished so need to sort it quick I know its still complies but not good at all on a new cable and install because this other spark says maybe damp in cable or skts due to coming from his shed I have had sockets from neweys ,B&Q MK which are rubbish terminals and get ,click a real mix and match slight damage from plumber her bruv etc he said its fine so they think it is

what about the voltage present from line to the wall 131v

I wouldnt mind but done all this work for free including alarm outside lights outside toilet ,shed supply and i am trying to do it perfect for them and I for the assesment i never try to do anything by short cut but wishing i hadnt bothered

 

[Deleted member 26818]

The fact that the reading rises during an extended test, indicates damp which is being boiled away by the test voltage.
Having voltage between line and the wall, indictes that the wall is providing a path to earth, probablly again due to dampness.
Try testing again with the CPC removed from the back box.

 

[Octopus]

Have you changed any of the sockets? I had a socket recently which was the culprit when it came to a lowish IR on a rewire!

 

[brucelee]

Thanks for the replies appreciated
yes tried changing the socket as he has bought some from B&Q DP switched ,some from his work and his shed ???? were its not good to keep electrical items and the rest were from Neweys think i have had to fit 4 different makes of skts

i have tried to locate with all sockets off, replacing the suspect ones, Linking out the suspect sockets with a new piece of cable so as to remove the possibility of the cable being damaged and still got strange readings
Only on the sockets and only on N-E
when i split and test each time i get the readings rising
IF I hold test button down I get the readings rising
tried N conductors to wall lower IR Line to wall 299 earth to wall 299
with the socket removed from wall still happens and from the conductors N to wall lower

I have another double on a wall within 2 metres and this is fine so is this wall

I noticed the gutters are leaking onto the rear wall with all the rain we are having and runs down to where the window is and were the socket is on the inside so this cant be helping with the PVC window being fitted inside the old wooden sash windows
under the stone sill there is water damage on the inside when i first chased water damge and all the plaster fell off it was like cutting cake
just crumbeld away

I tried as des said with the volt stick and nothing
then I tried with socket adapter and a Fluke t5 -1000 to check for voltage i disconnected the earth lead to back box I connected one lead of the votage indicator to the line of the socket adapter ad the other to the wall
and around the skt in a metre or 2 radius getting readings of
8v to 180v and there is a disconnected pipe under the boards and was getting about 220v this is all within a metre from socket
when i test the wall alone 0v when i test wall to pipe 0v
I even tried a stupid thing and put my hand on the wall and nothing
as I would rather it be me that gets a shock than her mum or dad

 

[IQ Electrical]

I agree with Spin here, it's almost 100% certainly dampness causing a climbing/falling reading like you describe.

I know this is a new installation but remember that you are getting an IR reading of 40,000,000 (40 million) Ohms here.

I'd assemble it, test it, record the values as they are and maybe pop back in a few weeks (it can easily take that long for the plaster to dry out fully)and measure the IR again out of interest.

On some large jobs where there are large expanses of plaster and buried cables, IR can plunge to single figures but you can measure it rising again each day if you're that way inclined!

 

[Farmelectrics]

i agree with iq 40mohms is a good reading fill in test sheets and get on your next job start earning money again

 

[Deleted member 26818]

I must admit, I would have expected the reading to drop with the earth to the back box disconnected.
Instead it appears to have risen from 131V to up to 180V.
Perhaps the pipe is to blame if it's earthed anywhere.
As has been said, the readings are within spec.
So how far do you go in order to find the cause of a less than perfect reading that's acceptable?

 

[tony mc]

I have to agree Dampness.

The bit about splitting it up & readings of >299 then as you rejoin the readings come down , dampness, with cables connected in parallel so a decrease in IR thats my opinion.

It takes weeks or even months to dry out completly.

I had a house which had been plastered and when testing all the plaster looked dry as a bone but the readings were down from what I expected on a new install. (It was like a green house inside the house with the sun coming in via the Velux windows but it was still damp underneath)

Testing a few days later and the reults were getting better so I left it for another few weeks and spot on >299 Meg on all tests.

IMO the wall will be damp giving you the voltage reading which will drop off as it drys out.

Best of luck with the assessment Bruce!!

 

[Deleted member 26818]

My tester shows >1000MΩ.
Makes you think anything below is dodgey.

 

[brucelee]

Thanks Guys

I appreciate all your wisdom and knowledge

Yes I know it complies and 40.000.000 ohms is still a high reading i expect it to be perfect lol like the rest
It was the voltage that i was reading between the line and the wall which was worrying me
and as it was showing between about 5v and 180v in different points this is with fluke t5 but with megger set on voltage range upto about 150 in differing points just moving the probes even slightly seems to affect how much voltage i get or IR


From the beginning before I even installed the socket on this wall it was clear there had been damp or water penetration as the plaster had blown and soon as i chased a large section fairly deep fell of completley to the brick about a 5 x 2 feet area
and on the stone sill thats under the window there was eidence of water marks the gutters are leaking they have only just bought this house
It had never been rewired
Had Lead sheathed cables that had completly crumbled at the accessories and the sockets were in VIR which had completly melted in full lengths
were it passed through from one switch to another on landing there were just bare conductors NO earths to lighting anywhere and the old sockets were earthed with bare copper to pipes

there were still lead gas pipes going up the wall to were there was old natural gas lights I removed it as i came across it
and all the old wiring and lead and copper has been removed except this one point in rear bedroom
there are new pipes but most of these are plastic apart from gas which is copper and copper at the bolier I have fitted 10mm to gas and water with unisualted crimps to BS951s
16mm earthing conductor 25mm tails
the Ze was 0.09ohms
PFC was 3.0kA
all continuity readings on sockets for r1 = 0.58, rn = 0.56 r2= 0.96
R1 + RN readings were between 0.26 and 0.29 except attic which is a spuur of FCU on landing this was 0.33
R1 and R2 were all within 0.36 to 0.39 ohms
R1 + R2 at the attic socket 0.44
up lighting was R1 +R2 =1.39ohms at second of the landing lights there is also a 2 way and intermediate incorporated in this
and 2 lights in attic
down lighting R1 +R2 = 1.03 at wall lights in lounge

IR on all circuits >299 except the N-E of the sockets at board around 180 sometimes others been as low as 40+ and as high as 299 but doesnt go off the scale like it does when says greater than 299 even though the megger i have only reads 299 you can see if it goes over this on the display with the needle on the meter
this circuit doesnt between the N-E

I have been well and truly baffled and spent forever trying to locate the reason why and only thing I can now come up with is moving this socket to the other wall with the other socket so the this will eliminate the damp issues

i have another point on this wall which will be to a outside light
I have run a 1.5mm to a fcu in kitchen then back up the wall to a single back box which will have a blank plate inside the connections will be made with helicons or wagos for the outside toilet light and the outside security light which i am thinking of telling them to get one of the new low energy ones

thanks to all you seem to be in a similar opinion to me that the damp is the issue
cheers DES, SPIN,MURDOCH, IQ, TONY MC, FARM ELECTRICS

 

[brucelee]

I hope when I move it this is the last i will see of this low IR as its drove me insane

I just have the alarm to test and commission and the kitchen as this is only at first fix stage waiting for the plasterer
5 circuits done and tested and 4 to go with a spare way for the future shed supply in 6 months I have already run the cable in for this in preperation
i have installed a large digital aerial and 4 points 1 living room 1 kitchen and 1 for each bed this is all done

just the cooker circuit
the oven circuit
kitchen ring and outside flood light and outside toilet light then done
all cables in
the outside light has a point on the damp wal in the suspect bedroom considering moving this as dont want to end up with same probs as i have with the sockets
I connected this circuit up with heliconns and Ir tested it but this one shows 299 on all but when it is powered up may have same prob as the sockets

cheers to all this is why this is the only forum i participate in and basically the only useful thing i ever found lol on the internet