Original and strange ring main readings RCD Tripping

[Roger]

Need some guidance from the wise old forum please

Have a issue with a rcd tripping,Thought I had issue with original marked downstairs ring so did continuity end to end at CU all ok after I did R2 cpc ,all ok whole house lights and everything,good values for cpc so that was ok .Did Cross connection l/cpc and n/l out and in, you know the figure of 8 to get the R1 and R2 readings.All the sockets in the whole house both floors seemed ok apart from 3 ! .1 socket in the UPSTAIRS bedroom and 2 sockets in the Downstairs front living room had high readings of 24.9/25 ohms everything else seemed ok with readings no higher than 1.10.For info front room had 4 socket the other 2 were fine.All sockets were wired as rings and had 2 cable entries no spurs.

Very strange so reconnected CU back up and then checked original marked upstairs ring,end to end ,cross connected and the 3 sockets with high readings seemed fine with acceptable readings.Out of interest checked other sockets that were ok with first tests and they all had voltage so could confirm that they were all feed from the so called downstairs ring.

Question why the high readings ? ,ring main crossed somewhere ?

For info they had a socket in the toliet,only a small room and a child could pee on it easily.I think every light switch needs replacing as they all feel very worn and gritty when switching.Old house again for info she did want the meter relocated moved down the into the hall about 4 foot ,Electricity board quoted £1500 and could not do it for 9 weeks.No more than 4 hours work tops.,

She's just getting the house back together she will be very annoyed if I have to pull floorboards up.

Any ideas ?

 

[Des 56]

I dont quite follow the problem solving
You say you had a problem with RCD tripping
Then you describe ring continuity tests

Did you change the consumer unit?

 

[electricAl]

Unless you`re describing the R1+R2 tests conducted for another reason, i`m equally puzzled as to the association.

If an earth leakage clampmeter wasn`t to hand then i`d have been looking at the insulation resistance readings with interest, not continuity - no direct relationship with RCD tripping.

Or is there more to the problem than meets the eye?

 

[Roger]

More info, yes CU change,since change when switching various appliances RCD trips that services those circuits.

Tests were completed to establish ring was ok ,a good place to start one thought ,the logical step !

Or not !

Not strange that I had 3 sockets ,2 downstairs,1 upstairs with identical high readings.

I am back there tomorrow hopefully and will do insulation tests (did not have it with me today )on upstairs ring and see what I find.

Any other pointers to look for.

 

[electricAl]

Sympathise with your predicament, but also with the customer too.
Altho i`m sure you don`t want to hear it right now, this is exactly the kind of situation you can find yourself in if you don`t carry out at least rudimentary tests before changing the CU.
In fairness to your customer, i wouldn`t be too impressed either, seeing as without being advised of the distinct possibilty, she`s now got an non-functional installation. And facing the possibilty of having disruptive remedial work done that she hadn`t anticipated. Probably some way off what she visualised after having a new spangly CU fitted.
And as you`ve now dicovered the RFC is screwed up, you`re obliged to sort it one way or tother

Anyway, thats no help to you at present.
I only read your post thru quickly the first time around, & on looking a little more carefully, those readings are virtual no readings. Clearly a very poor or even broken connection somewhere. Somewhat unsure of your summarisation Roger - are you saying you`ve got 2 RFCs and a connection between them. What were the IR readings BTW. They may tell us something...
As to the original problem of RCD tripping, if it only popped when something is switched on (an appliance) it may be unrelated, but i would double check your Neutral terms in the board - if you do have 2 RFCs then i`d assume you`ve got one on each RCCB? Ensure the respective neutrals terminate in the correct N bars.

Be interested to know how you get on with it.

Al

 

[Roger]

Sympathise with your predicament, but also with the customer too.
Altho i`m sure you don`t want to hear it right now, this is exactly the kind of situation you can find yourself in if you don`t carry out at least rudimentary tests before changing the CU.
In fairness to your customer, i wouldn`t be too impressed either, seeing as without being advised of the distinct possibilty, she`s now got an non-functional installation. And facing the possibilty of having disruptive remedial work done that she hadn`t anticipated. Probably some way off what she visualised after having a new spangly CU fitted.
And as you`ve now dicovered the RFC is screwed up, you`re obliged to sort it one way or tother

Anyway, thats no help to you at present.
I only read your post thru quickly the first time around, & on looking a little more carefully, those readings are virtual no readings. Clearly a very poor or even broken connection somewhere. Somewhat unsure of your summarisation Roger - are you saying you`ve got 2 RFCs and a connection between them. What were the IR readings BTW. They may tell us something...
As to the original problem of RCD tripping, if it only popped when something is switched on (an appliance) it may be unrelated, but i would double check your Neutral terms in the board - if you do have 2 RFCs then i`d assume you`ve got one on each RCCB? Ensure the respective neutrals terminate in the correct N bars.

Be interested to know how you get on with it.

Al

Many thanks for that,LESSON learnt with tests first.To be honest the customer sort of expected some problems,I dont know why maybe something in the past has happened.I did also explain she might get some tripping with a new CU and if she had problems it would highlight them.I had originally thought the ring main was bridged somewhere(in experience).I will do insulation resistance on the circuits and let you know my readings (BTW ?)
One further thought when I was testing the downstairs ring I had assumed the 2 questionable downstairs sockets where part of that ring .At that point the upstairs ring was still live ,so knowing what i do now those sockets should have shown voltage.My tester beeps and warns me if sockets are still live and this did not happen.Another lesson leart here switch everything off.The plumber wanted a cuppa so I told him to use the upstairs ring.I tested those questionable sockets and getting my r1 and r2 high values was with them in theory live !!! they were all connected to the CU.

I am getting confused and will return after a logical methodical fault process is put in place.
The CU has two RCD's and the neutrals are on seperate terminals blocks.Thinking about it the one socket I did not pull off was in the bedroom upstairs.Young daughter never seen so much clutter in a girls room,fitted bed and everything pilled around it.

Thanks again for you help ,i enjoy getting the old grey matter challenged

 

[sparky paul]

Have you checked for borrowed neutrals

That tends to trip rcd`s

 

[old dog]

it sound like you have crossed your nuetrals over. will the rcd trip as soon as you plug something in ?

 

[Yooj]

Hi Roger,

BTW = By the way...

On a differnet note, and this is not aimed at you Roger as I think you will insist on testing from now on on any subsequent CCU changes, but for the benefit of trainees, new sparks etc reading this...But whenever I do a CCU change, I always, always do a PIR on the whole installation first...dependent upon the size of the installation, this does tend to add 3 or so hours onto the job, but certainly in older houses, it is time well spent with regards to some of the horror stories I have uncovered in the existing installation.

As part of my quote, I explain the need for the PIR (I don't add much onto the overall cost of the work for this), and in some cases also provide a copy of the ESC Best practice guide for CCU changes (here's the link: http://www.esc.org.uk/pdfs/business-and-community/electrical-industry/BPG6_09.pdf ) See section 8 - Risk assessment.

Once th client reads through this, they usually concur with you, and realise that you are not trying to diddle them.

Anyway, Roger good luck with the fault finding, and let us know what you find out.

Yooj

 

[patricklondon]

very interesting thread. fair play to you roger for being honest and open with a mistake that many would be to proud to admit in a forum like this.
A mistake in test procedures have provided you and hopefully many others an invaluable lesson and save such a thing becoming a habit or bad practice. saving time, money on unpaid remedials, embaressment for having to explain a mistake and most importantly the risk of injury fire etc.
some good follow ups from the lads. cheers

 

[Roger]

very interesting thread. fair play to you roger for being honest and open with a mistake that many would be to proud to admit in a forum like this.
A mistake in test procedures have provided you and hopefully many others an invaluable lesson and save such a thing becoming a habit or bad practice. saving time, money on unpaid remedials, embaressment for having to explain a mistake and most importantly the risk of injury fire etc.
some good follow ups from the lads. cheers

Hi there,Mistake being that I did not test first ? interesting and informative post from Yooj,many thanks.

With the sockets being randomly spread around the house 2 down 1 up ,is that ok to leave assuming I can find the fault ? should I just rewire the sockets to the correct ring ? however the real pain is the downstairs ones with the feeds are under the floorboards where as others are dropped down from 1st floor.I would do a sheet to identify all sockets to the client so she would know exactly what MCB/RCD covers what.

The client is cool and chatted with the plumber offering to pay me money to sort it out ! he is the main contractor so everything goes through him. I popped in today and all neutrals are in the correct bars on the CU,thats all I could do (van problem)

I might put a RCBO on the ring to maybe help stop the tripping as I am now not going back for about a week as her kitchen stuff has been delayed.

Thanks to all for your help,I could spend hours on here its very interesting.

 

[Phil Mumford]

RCD tripping is going to become the lifebood for many an electrician in the future.

Neutral/earth faults will be their main provider of income. Tricky to nail down (no pun intended). Can trip an RCD through a fault on another circuit - may even be load dependent - more load more trips !

Cross connected rings/radials, borrowed neutrals, incoming loose neutrals and 'the bloke next door' plastering a live conductor into the wall, are some of the ones I have come across.

I have even had to remove RCBO's and install RCD sockets because you cannot rip up the floors to find the fault.

Welcome to my world

 

[Davey101]

I once tested a job (local hospital), and everytime I used my 'walkie talkie' to speak to my mate, it would trip two or more RCBO's at the board!
Started shouting to each other after that!
Also managed to nail through a cable on a new kitchen I had just wired,causing the rcd to occasionally trip. I carried out insulation tests over and over, all was clear. My mate removed a length of sheathing, and found the problem. Try all the obvious, and carry out all tests, but bear in mind that it could be caused by pretty much anything, as Phil suggested.
Also, rare as it may be, it 'may' be a faulty RCD.
Good luck

 

[Roger]

A quick update and a quick fix the RCBO fitted to the defective ring has actually cured the problem,no more tripping.Happy client however the problem still exists and I am obliged to sort it out.

Hopefully I'll get a free day and investigate further.

Remove every socket fascia ,unscrew and remove wires and go socket feed to socket feed to establish actual ring and routing of the cable direction and while I am doing that do a insulation test to check each wire.Blimey another day it was only a kitchen refurb with a new CU !.

 

[Davey101]

A quick update and a quick fix the RCBO fitted to the defective ring has actually cured the problem,no more tripping.Happy client however the problem still exists and I am obliged to sort it out.

Hopefully I'll get a free day and investigate further.

Remove every socket fascia ,unscrew and remove wires and go socket feed to socket feed to establish actual ring and routing of the cable direction and while I am doing that do a insulation test to check each wire.Blimey another day it was only a kitchen refurb with a new CU !.

Just a quick note mate, if you carry out an IR test on the whole circuit, or indeed the whole installation, you shouldnt need to test every cable individually (presuming that the 'whole circuit reading' was clear of course).
A 'figure of 8' test is very important as well, especially on the neutrals, to make sure that you have the correct neutrals connected to the correct RCD. Personnaly, I would connect the live and neutral, and then check all sockets on that circuit. I would also test all sockets on the OTHER circuit as well, to try to eliminate shared neutrals. An IR/continuity test between the different neutrals at the board, and in the field may be usefull as well.
If your unsure, its always best to carry a martindale, or volt stick (ducks for cover) when you are sticking your IR tester on something which 'could' be live.
Not sure what the first line of your post means.