I was advised that I should not export the earth from my house and to TT it at the shed. Plastic water pipes and timber frame.
Who by?? This is an old iet article but the principles still apply:
http://electrical.theiet.org/wiring-matters/2005.cfm[/QUOTE]
To be fair, it's probably worth pointing out that this is a much-debated issue and that a good few electricians appear to be less than fully happy about exporting PME earths to outbuildings.
The IET article presents local TTing and exporting of a TN earth as the two possibilities, without any discussion of the pros and cons and without indicating any 'preference'. They also only talk about earthing systems at all in the context of outbuildings which have extraneous-conductive parts (like metal water pipes), leaving it not totally clear as to what they are suggesting/proposing about earthing in situations (like the OP's) in which there are no extraneous-c-ps. I suppose that, by silence on the issue, they are implying that one should simply export the house's earth (whatever type it may be) in that situation?
However, as I and others have suggested in the past, issues comparable with those arising because of the presence of an extraneous-conductive-part can, and often do, exist in the
absence of an extraneous-c-p in the outhouse - for example, if (as is quite common), there is a metalclad light switch just inside the door, which can (and often will) be touched by someone standing on ground just outside the building (possibly with bare wet feet) - or if there are Class I light fittings with exposed-c-ps on the outside of the building. The risks are undoubtedly extremely small, but seemingly no smaller than those which would be posed by the existence of an extraneous conductive part within the building. I am therefore not convinced that the presence/absence of extraneous-c-ps is necessarily the whole of what (should) needs to be taken into consideration.
Kind Regards, John