Following my quering of the current RSGB Guidence on PME Supplies and RF earthing , There will be shortly be amended guidence leaflet. I've queried the document on several points, Current network repair guidence,changes to Part P reporting,etc
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For Those that dont Understand Uk Earthing there are 3 Earth systems currently in use
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TT - ?No supplier Earth, Local Earth provided by Earth Stake/rod, supply must be fed from a RCD
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TN-S Neutral and Phase supplied seperately,Earth is outer of supply Cable- This used to the main type of Installation
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TN-C-S or PME Phase, Neutral and Earth combined on single conductor, - This is main earthing system now in use, The Combined earth Neutral should be spiked at several points along the supply
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All new supplies are PME unless conditions or Location mean a TT is applicable
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The problem now is all network repairs are done with TN-C-S ?or PEN Cable, so you could have TN-S at your cutout,but 6 foot outside you could be jointed with PEN. So now it's wise to assume you have a PME connection unless there is definite proof otherwise.?
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The problem with a TN-C-S (PME) supply is if the Neutral fails and you have a RF earth,Your RF earth will take the Full Load current of your house and possibly several neighbours Houses. It's rare but can Happen
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So if you have a Rf earth it should be able to carry the full load current,?
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There are ways to minimise the risk ie additional earth rod at your point of supply ,but your Rf earth must be connected to this point and still be in ?suitable sized cable to BS7671, But if you have a additional Rod this becomes reportable under part P and must be Installed by a approved electrician or you need to notify Building control yourself and pay the testing.
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Or you could convert your shack to tt, but all earth supplies in this room, Including pipes and services must be isolated from the main earth by 2m, not always possible, Again if you do this it's reportable work.
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If you have a shack in a outbuilding,then it should be a TT supply, again this is reportable work.
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As you can see what started off as a simple exercise, now ?becomes a minefield.
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Ian
2E0IJH
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