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.
Being sized for both earthing and bonding.......... well now what - add the two sizes together I suppose. I know asked this same question last too............darned if I can remember the answer.
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
KC83:
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?
Generally, but not necessarily. I think that one has to be precise about the nomenclature. If "main earthing conductor" is the earthing conductor of the entire installation, I cannot think of any circumstances when any bonding would be larger than it. So earthing conductor selected i.a.w. Table 54.7 and main protective bonding conductor selected i.a.w. Table 54.8.
If "main earthing conductor" means the link between the two parts of the building, it could be smaller than the bonding - see Andy's garden shed example above.
For a combined conductor, just select the bigger of the two.
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