Another newbie insulation testing question...

Discussion in 'Electricians' Talk' started by Beacon, Mar 27, 2019.

  1. Beacon

    Beacon Member

    Thanks all.
    I’m going back to the site tomorrow so will report on technique in post 28 and give more information.
  2. Beacon

    Beacon Member

    Hi again.

    So, I've found the bad circuit. I set up for a global test and went through the MCBs. All was well but one.
    It's a ring final that runs pretty much all of the 2 storey cottage, less the kitchen. Isolating L/N/E from the CU and testing L+N to E gives same result.
    I've been round the house twice and in the loft to try and be sure everything is disconnected - no difference.
    So I split the ring to see if I could narrow the search area. Guess what? The ring is crossed at some point.

    Ideas for nest steps?

  3. Risteard

    Risteard Well-Known Member

    NEVER disconnect the cpc for insulation testing. As in not ever. It is a flawed and non-compliant test.
  4. spinlondon

    spinlondon Screwfix Select

    I thought we’d done this?
    You can disconnect whatever you want, if it aids fault finding.
    Andy_1983 and Sparkielev like this.
  5. Comlec

    Comlec Screwfix Select

    It's not worth it Spin - leave the NICEIC/RECI nitpickers to run their own world whilst the rest of us get on with our work in here - being polite and helpful to others.
  6. Coloumb

    Coloumb Screwfix Select

    I don't know what the deal is with payment or your customer, but if it was me I would find every and disconnected every jb/socket/fcu etc and test each length of the ring until you find the fault. The good news is at least you narrowed it to the ring and the ring doesn't include the kitchen. Once I had a very similar issue and it turned out a slug had got inside. Testing a backbox in wet plaster can make odd things happen.
  7. Coloumb

    Coloumb Screwfix Select

    HE is fault finding. Once he has found the fault he can do the poxy test with the CPC connected and issue the EIC. Do you want to help him or no?
  8. Beacon

    Beacon Member

    Chaps - good news - I found the fault.
    The ring final that showed the fault had a hidden spur to the garage (suspect t£e under slabs...) which had a RCD protected socket with a drill battery charger plugged in. ***.
    While frustrated, it’s good to start gathering the real world bits of experience that will be useful forever.

    So, thanks for the support and wisdom. I joined this forum as some of the other’s seemed officious and unwelcoming. It seems I made a good choice
    I’m sure I/we can ignore the smart arses, messianic and idiots. Just be grateful you don’t have to go to the pub with them

    Lots more to learn; thanks again.
  9. spinlondon

    spinlondon Screwfix Select

    Nice one.
  10. Coloumb

    Coloumb Screwfix Select

    Right, well don't forget to connect the earth :p:p:p:p;)
  11. Risteard

    Risteard Well-Known Member

    What's your point? Hiding a fault to Earth which isn't a fault to the cpc hinders fault finding - in no way does it aid it. Have some wit about you and realise the reason for the requirement.
  12. spinlondon

    spinlondon Screwfix Select

    Disconnecting the CPC will establish whether a neutral or line to earth fault is to the CPC or to some exterior earthed conductive-part.
  13. Bazza-spark

    Bazza-spark Screwfix Select

    Look, I have been in the trade since 1973, long before you were born. Disconnecting the cpc for fault finding is quite acceptable. When I was serving my time correct practice was to "isolate the suspected faulty circuit". That is what the OP has done.

    When he comes to carry out his final test for the certificates it will be with all conductors and circuits connected.

    Oh yes, and you hadn't spotted it wasn't a fault to earth when supposedly advising the OP with your infinite wisdom (not!). In fact I don't see any helpful, constructive advice - correct or otherwise - at all, like most of your posts.

    Note: Think carefully before you post an abusive reply.
    Coloumb and Comlec like this.
  14. Coloumb

    Coloumb Screwfix Select

  15. spinlondon

    spinlondon Screwfix Select

    What what?
  16. Mr Rusty

    Mr Rusty Screwfix Select

    titter ye not in the back row.......:p:p:p:rolleyes:
  17. Beacon

    Beacon Member


    More testing shenanigans.
    I'm working in a bungalow that's had a floor added. All wiring was in the old loft, but is now under the 1st floor, so I can't get to the junctions, LV lighting transformers etc etc.

    So how do I test circuits I can't fully disconnect?

    I figured L+N to E would be the way forward - with the line conductor out of the MCB, linked to the N busbar, and E picked up at the MET. This still gives very low results on the LX final circuit, and the socket ring final as it happens.

    In all cases the main isolator is off and the main supply earth is connected to the MET (!!!!)

    So it's a 2 part question:
    1. What to do if I can't disconnect accessories?
    2. Why doesn't a L+N to E test get round these issues?

    Thanks guys
  18. peter palmer

    peter palmer Super Member

    As per earlier in the thread - what part of disconcerting the neutral do you not get?
  19. chippie244

    chippie244 Super Member

    Do you tell the neutral his Mother didn't love him :):)
  20. Beacon

    Beacon Member

    Forgive the hard of understanding, but I know which circuit I have a problem with, and the 2-pole main isolator is off so there is no connection back to the step-down transformer and therefore to supply earth, so why would disconnecting the circuit neutral have an effect?

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