Another newbie insulation testing question...

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

  1. Beacon

    Beacon New Member

    Hi all

    I'm a recently qualified domestic electrician, struggling to come to terms with the reality of testing for certification - it's a joy isn't it?

    The whole thing is a ball-ache, but I have a particular problem; insulation resistance testing on a pre-existing domestic installation.

    It would be a lot of work to locate and remove/disconnect every accessory on the lighting/power ring finals and finals - so I'm doing L&N to E tests. Problem is, even doing this I'm getting close to zero results at 250v. I've tried using the busbars and MCB outlets, and disconnecting the live conductors and earth from the CU - still getting nowhere.

    Please - any wisdom/ideas greatly appreciated. 2 hours work installing followed by 3 hours trying to do the bl**dy tests isn't funny, or economic.
    I'm prepared to be stupid/wrong/ignorant, and am always ready to learn.
     
  2. Bazza-spark

    Bazza-spark Well-Known Member

    It sounds like you are being caught out by the star point at the transformer giving you false readings.

    You need to make sure the incoming earth and neutral are not in your test circuit.

    Hope that makes sense.

    Kind regards
     
  3. Beacon

    Beacon New Member

    Thanks Bazza - I thought I'd allowed for this by disconnecting all circuit conductors - could there be a link between separate circuits that is giving an alternative path to N do you think??
     
  4. Risteard

    Risteard Well-Known Member

    You shouldn't be disconnecting the cpc as it needs to be connected to the means of Earthing for the installation for the test to be valid. Ideally test the whole installation in parallel, otherwise you will need to calculate resistances in parallel to verify compliance with BS7671.
     
  5. Bazza-spark

    Bazza-spark Well-Known Member

    Rubbish!

    You need to disconnect when testing a ring to verify ring continuity, polarity etc.

    Stop giving incorrect information.
     
  6. Bazza-spark

    Bazza-spark Well-Known Member

    Have a look here http://www.sparkyfacts.co.uk/Inspection-and-Testing-Insulation-Resistance-Test.php and see if it helps.

    Kind regards
     
  7. Coloumb

    Coloumb Well-Known Member

    What exactly is it your testing the whole install for? You only need to test the ctt. you have altered, not the whole thing. Is this for a EICR? If it is then are you sure you have the experience to be doing them yet?
     
  8. Risteard

    Risteard Well-Known Member

    Verifying ring continuity has nothing to do with insulation resistance testing so you are the one talking absolute ****. If you don't understand BS7671 then cease from giving false information about it. Leave the real work of informing people to the Electricians amongst us.

    And in the meantime study Regulation 643.3.2
     
  9. Comlec

    Comlec Well-Known Member

    For anyone interested

    643.3
    BS 7671 requires that insulation resistance is measured between all of the live conductors and between the live conductors and the protective conductor with the protective conductor connected to the earthing arrangement. This key change to how the procedure currently worded was introduced in the 17th Edition in 2008 and is an important change to practice for many installers and inspectors. Taking cables as an example, previously it was acceptable to test a cable between the various cores, and test to earth (which was actually only the cpc, such as a single core conductor, or the armouring or sheath of the cable); sometimes these cables were terminated without further testing. This is not acceptable now and it is essential to test to the protective conductor (such as armouring) with it connected – via a fly-lead if necessary – to the installation earthing arrangement. This is shown in Figure 2.4c. It is a good idea to test all cables, including those tested during the construction stage using this method.
    (IET)

    IET. Guidance Note 3: Inspection & Testing, 8th Edition, 8th Edition. Institution of Engineering & Technology (IET), 07/2018. VitalBook file.
     
  10. Risteard

    Risteard Well-Known Member

    Indeed, but note also 643.3.2 - this is fundamental and has persisted throughout various Editions of the Regulations.
     
  11. Bazza-spark

    Bazza-spark Well-Known Member

    I perfectly well understand inspection and testing. Your post intimated the CPC should not be disconnected when testing. I poijnted out an instance where it needs to be.

    If you wish to comment post replies that a non-spark can understand.
     
  12. Risteard

    Risteard Well-Known Member

    It mustn't be disconnected for the insulation test - so talk of ring final circuit continuity testing is bogus and shows you up for someone who has no clue what he/she is talking about.

    Cease and desist from such nonsense posts which promote flagrant breaches of the Regulations.
     
    Last edited: Mar 27, 2019
  13. Comlec

    Comlec Well-Known Member

    Mmm - the sweet smell of law breaking.

    Nice typo tho’
     
  14. Comlec

    Comlec Well-Known Member

    @Beacon do you have, or have access to, a copy of The most recent edition of Guidance Note 3. Might help with your testing.
     
  15. Bazza-spark

    Bazza-spark Well-Known Member

    To tell a beginner that he shouldnt be disconnecting cpcs without explaining why is irresponsible and showsyou have no consideration for others as proved in the post regarding the poor soul with the cooker.

    I suggest you follow your own advice and
    until you can string a coherent and understandable answer for beginners and non=sparks to understand.
     
  16. Risteard

    Risteard Well-Known Member

    LOL, flagrant obviously.
     
  17. Risteard

    Risteard Well-Known Member

    The entire topic relates solely to insulation testing so your point is ludicrous and invalid.
     
  18. Coloumb

    Coloumb Well-Known Member

    Yes lol indeed. Had it been me you would have got right off on it. "ooooh look he can't spell, he isn't a spark etc etc. Look in your own backyard next time.
     
  19. peter palmer

    peter palmer Well-Known Member

    Maybe there is a fault on the circuit.
     
    Paco de Lucia likes this.
  20. Bazza-spark

    Bazza-spark Well-Known Member

    You really do twist things to try and make you look good and hate it when you are picked up.

    Made you put your website right though didnt I!
     

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