Exporting tt earth

[EFLImpudence]

Page 6 deals with the Earthing Conductor & Main Protective Conductor.

Where it says that your EC csa is dependent on the size of the largest phase conductor, what is the relationship between the two? Please.

 

[JohnW2]

I agree about isolating the tap but "nobody" does that ...

I'm not so sure about that, particularly if it's a DIY job - there are plenty of kits like this one

.... and yet "the same people" insist on TTing outbuildings which may be no farther away from the MET.

I still don't see (in this context) the relevance of the distance - as far as I am aware, the main concern, in some's people's minds, relates to the very rare occurrence of the MET of a TN-C-S installation rising to a very high potential relative to true earth - and that would be as much a problem if the outbuilding was 2 metres from the MET as it would if it were 200 metres away.

Kind Regards, John

 

[EFLImpudence]

I'm not so sure about that, particularly if it's a DIY job - there are plenty of kits like this one

Well yes, but I doubt it is like that because of what we are discussing.

I still don't see (in this context) the relevance of the distance - as far as I am aware, the main concern, in some's people's minds, relates to the very rare occurrence of the MET of a TN-C-S installation rising to a very high potential relative to true earth - and that would be as much a problem if the outbuilding was 2 metres from the MET as it would if it were 200 metres away.

It's not relevant but (some) people advocate TTing an outbuilding because they dislike "exporting" the TN earth but don't consider an outside tap which may be farther away.

 

[JohnW2]

It's not relevant but (some) people advocate TTing an outbuilding because they dislike "exporting" the TN earth but don't consider an outside tap which may be farther away.

Well, in that case we can probably agree that 'they' simply aren't being logical or consistent. However, for a person (not me) who is concerned about the extremely low risk that we're talking about, I suppose that their mistake is in not realising that it also applies to the tap, not in being concerned about "exporting" a TN-C-S earth to an outbuilding.

In fact, accepting that it is an incredibly small risk that they are worrying about in the first place, I would think that the tap probably poses a (relatively) greater potential hazard than do most outhouses to which a TN-C-S earth is "exported", particularly if the outhouse doesn't have any extraneous-c-ps.

Kind Regards, John

 

[Risteard]

Where it says that your EC csa is dependent on the size of the largest phase conductor, what is the relationship between the two? Please.

Sorry, missed your question.

The earthing conductor must be an insulated copper conductor.

For domestic the tails are generally 16mm^2. With 16mm^2 tails the earthing conductor must be a minimum of 10mm^2. Where buried if not mechanically protected by steel/heavy duty PVC conduit then it must be a minimum of 16mm^2.