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CSA of main earthing conductor for TT

Grumpy
Morning! Has the minimum CSA of the main earth to the rod changed in the 18th ed? I can't find any reference to it in the BBB (except when buried). 

I have a guy who is insisting on 16mm whereas I "thought" it could be much less if not buried and protected against corrosion and mechanical damage. I only have table 4.4(ii) in my 17th ed OSG as corroboration. Thanks.
  • 0
    He is probably applying Table 54.7 protective conductors sized according to line conductor size. If line conductor is smaller than or equal to 16mm2 the protective conductor is required to be the same size if of the same material.. 


    If the line conductor is greater than 16mm2 up to 35mm2 than the productive conductor shall be 16mm2.


    Z.


  • 0
    No it hasn't changed.  2.5mm where mechanically protected, 4mm otherwise. Unless your Ze is a few milliohms of course! Reg. 543.1.1. I must admit I tend to use 10mm anyway as it is more noticeable. That is TN Z.
  • 0
    Unless the rod has a spectacularly low resistance to terra-firma, a bit of 2.5mm would do, so long as well protected against mechanical failure,  and this is reflected in the 18th edn  UK regs - which I do not have to hand or I;d give you the para number.

    The OSG does( or did at least) also say this.

    mike.
  • 0
    Thanks both. So, are we saying that if you can't do the sums then you have to use 16mm? There isn't a definitive statement in the BBB like there was in the OSG?

    Mind you he only "presumed" the main earth was 6mm instead of 16mm so am I to assume he couldn't find one? Surely that might have been worthy of a comment, as might the presence of three electric showers, disconnection times of 0.4 and 5 seconds . . . I'm beginning to wonder if I've wasted my dollar!!
  • 0
    543.1.1 allows you to go down to 4.0mm2 if certain conditions are met.


    Z.
  • 0
    And thanks to you too Mike, sorry crossed. The para would be most helpful.
  • 0
    I used 10 mm last week, not because it needs to be that big but it looks the part. Without looking in the book I would say 2.5 mm would have been okay.
  • 0
    Zoomup:

    543.1.1 allows you to go down to 4.0mm2 if certain conditions are met.


    Z.


    I get that Zoom but the man still has to do some sums and if he can't then the default appears to be 16mm. He could do with a nice numpty table like that in my 17th ed OSG!


  • 0
    Sparkingchip:

    I used 10 mm last week, not because it needs to be that big but it looks the part. Without looking in the book I would say 2.5 mm would have been okay.


    I agree Andy, I always use 10mm. To me, stating that 16mm is required and a C2 undermines his credibility. As do the wrong disconnection times.


  • 0
    Grumpy:
    Zoomup:

    543.1.1 allows you to go down to 4.0mm2 if certain conditions are met.


    Z.


    I get that Zoom but the man still has to do some sums and if he can't then the default appears to be 16mm. He could do with a nice numpty table like that in my 17th ed OSG!




    There is still a "numpty table" in OSG, but it is now Table 4.4(iii).


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