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Discuss Main bonding..... yet again! in the Electrical Forum area at ElectrciansForums.co.uk.

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  1. happyhippydad
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    happyhippydad Member Electrician's Arms

    Location:
    Gloucestershire
    Afternoon all..

    Settling down to a fancy coffee from the new fancy coffee machine and as you do on a sunday afternoon I started thing about bonding :).

    Quite often the kitchen fitter, DIY homeowner etc has built around the Main bonding connection for the water and it is neither visible or accessible.

    It can be costly for a new bonding cable to be run especially when there 'may' already be one but it is just not visible.

    Previously if I saw a 2 x 6mm or 10mm cables leaving the CU (as well as the Main earth) and the water incoming pipe tested as 0.05 ohms or less to earth I would class it as having a satisfactory bond. However, it rarely comes back as 0.05 ohms or less so a new cable is needed unless I take part of the kitchen cabinet apart and see the cable.

    Also, the 10mm cable leaving the CU may not actually go to water and the water may just be joined to another earthed pipework with a 1mm somewhere thus giving a good reading to earth.

    What do you lot do when you cant see the Main bond clamp?

    Cheers everyone.
     
  2. anthonybragg
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    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    Take the bonding conductor out of the MET wandering R2 lead test use a mirror/camera on phone up behind the unit.
     
  3. happyhippydad
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    happyhippydad Member Electrician's Arms

    Location:
    Gloucestershire
    Thats pretty much what I do Anthony, however what would you do if you cant see the connection and lets say you get a reading of 0.2 ohms?
     
  4. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    cheshire/staffordshire
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    Telectrix
    you're wrong there about the 0.05 ohms. that is the max. reading you should get from the boding conductor to the extraneous metal to which it is bonded ( I.E. across the clamp.) it is NOT the resistance of the cable.
     
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  5. Baker1988
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    Baker1988 Electrician's Arms

    Location:
    Kingston Upon Hull
    Use a wander lead and test to the water pipe to the bonding conductor in the board if it is less that 0.05 ohms then i would say its fine and just note down that the clamp is inacessable to view or check.

    Also agree with tel above 0.05 is not the cable its to the pipe it is connected to as you always test on the pipe not the clamp
     
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  6. Pete999
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    Pete999 Trusted Advisor

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  7. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    The 0.05 figure is a guide at best as it’s never been quoted in bs7671 only GN3 and it’s origin seems to be unknown
     
  8. spinlondon
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    spinlondon Trusted Advisor

    Location:
    Harlow Essex
    Another figure bandied around is 0.02 Mohms or 20 Ohms.
     
  9. anthonybragg
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    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    As mentioned before I am on a site gutted refurb and the floor has been cut out for a platform lift the floor where it has been cut out has been supported by metal girders bolted to the concrete purlins all metalwork has been sprayed with fire-resistant paint this is to the floors between ground and first and first and second opinions should they be bonded?
     
  10. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Are they accessible to touch?
     
  11. spinlondon
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    spinlondon Trusted Advisor

    Location:
    Harlow Essex
  12. Pete999
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    Pete999 Trusted Advisor

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    Northampton
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    Well I don't know it seems that the 0.05 ohms relates to the resistance of the banding conductor and the connection vis the Earth clamp on the pipework, it does seem quite clear from GN3 and the numerous you tube videos from respected engineers that the case involves the bonding conductor AND the earth clamp's connection to the pipework. As can be seen from the statement that the length of the Main bonding conductor has some bearing on the problem. One statement suggests that anything over 25mtrs the conductor csa should be increased, which in my eyes confirms that the resistance reading does include the bonding conductor, and not just the resistance of the pipe and the earth clamp. I do agree with some that the reading should be taken from the disconnected bonding conductor and the PIPE as described in the video that was posted earlier. Just saying.
     
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  13. Pete999
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    Pete999 Trusted Advisor

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  14. anthonybragg
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    anthonybragg Electrician's Arms

    Location:
    NORTHAMPTON
    Business Name:
    CHARLTEC ELECTRICAL LTD
    They are covered with the paint.
     
  15. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    No it’s extraneous conductive parts in general as explained in the link
     
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