There is always a question of if it is better to earth random bits of metal or leave them 'floating' -  the question is what sort of fault you guard against.If the post is well earthed, but you are holding a damaged extension lead with an exposed live core, you may prefer it not to be earthed,  and indoors a similar argument may be made for kitchen sinks and faulty kettles, and advice about earthing sinks or not has varied over the years, with no clear wining strategy, except perhaps recently, to not worry too much but to fit RCDs instead.

If the installation is to be properly protected by equipotential bonding, you have to do everything, a half-and half affair can be worse than none.

You can achieve this indoors, but outdoors the idea of an equipotential zone rapidly becomes impractical, as there is too much stuff in reach that is casually earthed, fence posts, spades, wheel barrows, that cannot sensibly be bonded, and actually cannot sensibly become live either. For this reason kit for outdoor use, mowers, hedge trimmers etc are normally double insulated, and metalwork is self earthed to the ground it stands on by a fairly indeterminate impedance, depending how far it is hammered into the ground or is sitting in a puddle. (though a container sitting on its metal skids in the ground can be a fairly low impedance if the ground is damp and rich in organic matter - so farmland over clay is surprisingly good.)


However, if the metal work in question is part of the support or the enclosure for some class 1 electrics, so perhaps there is a credible fault path that might make it live, then maybe we'd rather it was earthed - again if the box or the light switch was metal, the same connection would be there via the fixing screws and brackets and no-one would question it, would they ?

It is not really clear-cut.

Ideally if we had the choice, the cable, the light switch and an fittings would all be double insulated and no CPC would be  needed - but that is not how most things are made.


Regards Mike


PS also where two SWA cables go into a plastic box, is often a weakpoint in terms of the armour and earthing continuity and current handling capacity, as it all funnels down onto a rather weedy little bolt  stuck into a painted metal or plastic box.

The pirahna nuts, and the related twin hole versions are much better in that way than banjos, which for my money should be omitted from the gland kits and  the nuts recommended instead, as indeed the likes of screwfix are doing.
    

Pirahna nuts in various sizes or Whiska 2 hole earth plate


M.

There is always a question of if it is better to earth random bits of metal or leave them 'floating' -  the question is what sort of fault you guard against.If the post is well earthed, but you are holding a damaged extension lead with an exposed live core, you may prefer it not to be earthed,  and indoors a similar argument may be made for kitchen sinks and faulty kettles, and advice about earthing sinks or not has varied over the years, with no clear wining strategy, except perhaps recently, to not worry too much but to fit RCDs instead.

If the installation is to be properly protected by equipotential bonding, you have to do everything, a half-and half affair can be worse than none.

You can achieve this indoors, but outdoors the idea of an equipotential zone rapidly becomes impractical, as there is too much stuff in reach that is casually earthed, fence posts, spades, wheel barrows, that cannot sensibly be bonded, and actually cannot sensibly become live either. For this reason kit for outdoor use, mowers, hedge trimmers etc are normally double insulated, and metalwork is self earthed to the ground it stands on by a fairly indeterminate impedance, depending how far it is hammered into the ground or is sitting in a puddle. (though a container sitting on its metal skids in the ground can be a fairly low impedance if the ground is damp and rich in organic matter - so farmland over clay is surprisingly good.)


However, if the metal work in question is part of the support or the enclosure for some class 1 electrics, so perhaps there is a credible fault path that might make it live, then maybe we'd rather it was earthed - again if the box or the light switch was metal, the same connection would be there via the fixing screws and brackets and no-one would question it, would they ?

It is not really clear-cut.

Ideally if we had the choice, the cable, the light switch and an fittings would all be double insulated and no CPC would be  needed - but that is not how most things are made.


Regards Mike


PS also where two SWA cables go into a plastic box, is often a weakpoint in terms of the armour and earthing continuity and current handling capacity, as it all funnels down onto a rather weedy little bolt  stuck into a painted metal or plastic box.

The pirahna nuts, and the related twin hole versions are much better in that way than banjos, which for my money should be omitted from the gland kits and  the nuts recommended instead, as indeed the likes of screwfix are doing.
    

Pirahna nuts in various sizes or Whiska 2 hole earth plate


M.