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Ground the steel floor structure?

I've just finished re-building a couple of resort bungalows here in sunny Thailand.


The bungalows were wooden structures on 2m concrete posts (bungalow on sticks), the outer shell and roof were teak and Burmese ironwood which were structurally sound but the floor was "cheaper timber" which the termites got.


So the floor is now a welded steel frame sitting on the concrete posts with "Shera board" (cement board) flooring.


Supply is a TT submain on a 10mA RCBO from the house which is TNC-S, mostly 2 pin outlets except for the fridge which is on a local ground rod.


So, should I earth the steel, either to the existing rod or to its own separate rod.


No wet rooms in the bungalow although there is an exposed balcony, all wooden handrails etc.


Thoughts.
  • I would be inclined to bond the metal floor structure to the existing ground rod. It may well be already fortuitously grounded, but an extra connection is very cheap and prevents any dangerous touch voltage between the fridge and the metal floor supports.
  • Is the metal floor an extraneous-conductive-part, or will it ever be such as in the rainy season? That is the deciding factor.


    Z.
  • I agree with broadgage - bond it to the existing rod. It is likely already earthed to some extent via the salts in the concrete posts. 


    Regards,


    Alan.
  • Thanks chaps, that's pretty much along my line of thought.


    On a related subject, I used to visit an office/factory on Wallisdown Road in Bournemouth which (at the time) was a steel single storey structure elevated on concrete columns, underneath was parking. Arriving one day to look at a faulty equipment (I was doing field service) I noticed some very conspicuously new copper "lightning conductor" strip running down many of the columns. Apparently there had been an "electrical incident" which had livened up the whole structure much to the chagrin of anyone who happened to be in contact with the steel and ground (it also caused the reason I was there). It's now the Parvalux factory, the building is still there but has now had walls added to create more office space (and less parking).
  • The Shera board flooring sheets can absorb up to 35 per cent. water. The rooms' floors will be damp I reckon, and electrically conductive.


    From the official company's website: " Our fibre cement boards, by their very make up, are truly moisture resistant and, although they do absorb moisture, it is able to escape. They can also be painted, which will repel moisture altogether."


    Yep, it sounds as though the floor sheeting can  become a slightly extraneous-conductive-part, but with a TT supply does that really matter?

    https://www.sheraeu.com/Boards.html


    Z.
  • The Shera is unlikely to be left naked (it just doesn't look very nice), although at this stage I don't know what floor covering will be used.


    Knowing the owner of the bungalows it will be the cheapest Lino type stuff he can get ?