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Earthing and Bonding

Former Community Member
Former Community Member
Hi All


Working on a scheme whereby we have a private transformer serving the site - TN-S arrangement. This comes into the building, we then split to feed a switchboard in one part of the building which is existing, the second split heads to a new build part which has the second switchboard. This new build contains swimming pool. The supply to the new switchboard is via a busbar 3L+N+PER. Question relating to earth bars - we currently have the main earthing bar at the intake point which is at the existing switchboard location - we then had cable feeding out to the new earth bar at the new switchboard location. Contractor is proposing that they remove this interlinking earth cable between bars, and take a bond directly from the new switchboard earth bar to the new earth bar in the room. Does this sound feasible - to me doesnt sound right, but I can't find anything specific to say not.


Many thanks
Parents
  • Former Community Member
    0 Former Community Member
    Zoomup:
    Contractor is proposing that they remove this interlinking earth cable between bars, and take a bond directly from the new switchboard earth bar to the new earth bar in the room. 


    Does the contractor consider that the existing combined earthing/bonding cable is too small for its functions? Why not ask the contractor for  his reasons?


    Does 312.2.1.1 Fig 3.8 help? The protective conductor (PE) normally carries very small currents in comparison with normal load currents, but may carry high currents during fault conditions. 


    Z.




    Thanks for the replies so far everyone - just to clarify, when I say remove this cable, its from the design (to save cost) and not an existing link. Essentially saying that the aluminium conductor within the interlinking busbar becomes the earthing and bonding conductor. So what i'm reading so far is that if the aluminium CSA is sufficient size to equal the main earthing conductor it should be okay to use this as both the protective earth and the bonding conductor?


    The arrangement would be main earth into main earth bar from DNO, bond from this earth bar to panel supplying the remote switchboard fed by interlinking busbar, bond from remote panel to local earth bar in the room, with all local bonding to that earth bar. 


    Any other thoughts welcome


    Many thanks


Reply
  • Former Community Member
    0 Former Community Member
    Zoomup:
    Contractor is proposing that they remove this interlinking earth cable between bars, and take a bond directly from the new switchboard earth bar to the new earth bar in the room. 


    Does the contractor consider that the existing combined earthing/bonding cable is too small for its functions? Why not ask the contractor for  his reasons?


    Does 312.2.1.1 Fig 3.8 help? The protective conductor (PE) normally carries very small currents in comparison with normal load currents, but may carry high currents during fault conditions. 


    Z.




    Thanks for the replies so far everyone - just to clarify, when I say remove this cable, its from the design (to save cost) and not an existing link. Essentially saying that the aluminium conductor within the interlinking busbar becomes the earthing and bonding conductor. So what i'm reading so far is that if the aluminium CSA is sufficient size to equal the main earthing conductor it should be okay to use this as both the protective earth and the bonding conductor?


    The arrangement would be main earth into main earth bar from DNO, bond from this earth bar to panel supplying the remote switchboard fed by interlinking busbar, bond from remote panel to local earth bar in the room, with all local bonding to that earth bar. 


    Any other thoughts welcome


    Many thanks


Children
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