Exported earth

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SparkyMarky

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Whilst doing my Part P course recently we got to discussing the wiring of a garage remote from the main house. We were told that whilst it was fine to link the swa to the MET the garage itself should have its own TT system, something to do with an "exported earth". This, apparantly, was outside the scope of the course and no further explanation was forthcoming. Could anyone explain exactly what is meant by this?

 

steptoe

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to be perfectly honest if you dont know how this works then you be best not doing this sort of thing.

in short this is a quick explanation, as I understand it, some1 else may no doubt correct me.

if the garage is a long way from the incoming supply then by the time you run the cable to it, along with the exported earth you may well find you have a substantial voltage drop,

it may sometimes seem ok on the meter, but remember with the earth we are looking at a possible fault current.!

by exporting the earth you are effectively extending the size of the equipotential zone, not the best idea.

I have actually seen certain installations where the earth conductor in the garage/shed was actually showing a voltage potential to the earth/ground outside!

theoretically this would mean that anyone standing on the ground outside the shed and touching any part of the shed that was connected to the electrical earth that had been exported would receive an electric shock.

as I mentioned, its not really the sort of thing that can be explained on a forum easily,

IMHO if you need to ask this sort of question then you may well be best advised to obtain the services of someone who knows and understands this type of installation.

regards, Albert. :)

 

SparkyMarky

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"to be perfectly honest if you dont know how this works then you be best not doing this sort of thing." Well, what a smug, self satisfied (if ungrammatical) reply that was. Has it advanced our sum of knowledge on the subject? Not one jot! The clue, Albert, was in the word "exactly" not "please state the bleedin' obvious". So it seems that this is beyond the scope of my course and beyond the scope of an electricians' forum. Golly, it must be complicated. How can an upstart like me ever hope to comprehend such complexity without at least 15 generations of my antecedents being electricians? I may as well burn all my C&G certificates and become a chippie. Thanks for your help.

 

steptoe

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try reading the rest of my post!!!!

and to be honest, having a pile of papers aint worth sh it if your thick and cant read more than one sentence at a time.!!!

are your C&G certs related to being an electrician at all?

if they are then you should already know the answer to the question you asked,

and since when did wiring a garage ever become anything to do with building regs? thats what part P is, a building reg, so perhaps asking a question on wiring a sub main to an external load was a stoopid question to ask in that situation.

like I said at the beginning, if you dont understand the basic fundamentals of sparking (for providing an earth is a very VERY basic subject) then I sure as hell aint gonna explain to you how to get someone killed cos your doing a half ar5ed job cos you dont even have the competence to change a 1362!!!

 

steptoe

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This, apparantly, was outside the scope of the course and no further explanation was forthcoming. Could anyone explain exactly what is meant by this?

it means the course didnt cover this subject.!!!

I would have thought that was self explanatory to someone with all your C&G papers. or didnt you get one in reading?

 

SparkyMarky

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I did try to read the rest of your post but it became increasingly incoherent. At my third attempt I did get a C&G in reading but, unfortunately, not in mind reading so I'm still not able to divine whether you know the answer to my original question. From the scorn and vitriol I suspect not. What else do you do with your evenings besides writing scathing and unhelpful posts. Do you masturbate because you certainly come across as a prize ******!!

 

steptoe

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so,,,

you dont understand voltage drop?

you dont understand difference of potential?

you dont understand the equipotential zone?

you dont understand PFC?

you dont understand the possibility of giving some1 a potentially lethal electric shock?

seems to me theres not that much about sparking you do understand.

maybe that chippie comment would be a better option for you after all.

Im only here to try and advise if you have a little bit of knowledge and are able to adapt the information to your own particular situation, obviously you dont have the knowledge to know your limits.

hence the comment that if you dont understand something then best to employ the services of some1 that does.

Im not a baby sitter.

like your part P friend said,

this forum doesnt cover the scope of trying to educate someone who knows it all already.

 

steptoe

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you run the SWA to the garage (assuming you have calculated for voltage drop etc and have correct size cable)

earth the SWA sheath at the house(supply) end only,

terminate it to a plastic CU or adaptable box or whatever at the garage side.

do NOT carry an earth of any description from the SWA(supply) to the garage.

drive an earth rod into the ground and from this run a 16mm or larger,(depending on sub main,or supply size) earth cable to the MET for garage.

there you go, garage is now separate TT system.

remember to allow selective RCD protection for your sub main and finals in garage.

and to route the SWA in prescribed areas.

is this what you needed?

 
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you run the SWA to the garage (assuming you have calculated for voltage drop etc and have correct size cable)earth the SWA sheath at the house(supply) end only,

terminate it to a plastic CU or adaptable box or whatever at the garage side.

do NOT carry an earth of any description from the SWA(supply) to the garage.

drive an earth rod into the ground and from this run a 16mm or larger,(depending on sub main,or supply size) earth cable to the MET for garage.

there you go, garage is now separate TT system.

remember to allow selective RCD protection for your sub main and finals in garage.

and to route the SWA in prescribed areas.

is this what you needed?
I believe that was the reply OP was looking for Albert. :)

Try not to get worked up Albert - Watch your blood pressure. OP was unsure - so he asked - That's what we are here for Sir... To help each other out. That where everyones experience comes in.

I am on the C&G course - although we had used swa, we haven't been told of the earthing requirements on long runs - So I can sympethise with the OP. I have picked up a heck of a lot of knowledge through buying books and studying, going to college, Prcticing in my workshop etc and more so from Guys like YOU, whom I respect.

I don't like forums that give carp replies, hence my reason for starting this one, Sir.

Let's keep it insult free (ish) & word it better. And that goes for us all - not just you Sir. :p

Now...Who's for a free Promo Sticker. :eek: :^O

I am off for a minute to order them.

:)

 
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Jamie:I can sympathise with Steptoe here m8. Sparkymarky DID come back at him a bit strong, you must agree. It isn`t the easiest thing to attempt to explain, although Steppy, that WAS a well written response.
Possibly six of one and half a dozen of the other???? ?:| :(

Not actual sure Sparkymarky has been given an explanation to his question..

{"exported earth". This, apparently, was outside the scope of the course and no further explanation was forthcoming. Could anyone explain exactly what is meant by this.}

don't think he was asking how you actual wire the SWA to the garage with a TT configuration with additional rod?

But I may of course be barkin up the wrong tree???

maybe even in the wrong forest?? ?:|

"Often outside the scope of the course" means the lecture don't know himself how to explain it!!! X(

been trying to think how to put my understanding of the term "exported earth" as simply as possible...without tying myself up in knots...

But my PC's anti virus has decided to go an do a "Full System Scan"..

so things are running a bit SLOOOOOOOWWWW at the moment!! :(

I may return shortly!

 
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I thought that on a TN system if there was no extraneous metal work in the oubuilding you could export the earth. There is a IET paper on this which i will look up.
I was under the impression it was a no-no on PME. As you say, will have to hit the books and find reference. ?:| :eek:

Yes, Jamie, I agree. :) Wasn`t having a go m8. :eek: Could just see myself getting a bit het up with that type of reply. ]:) ] :)

 
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Whilst doing my Part P course recently we got to discussing the wiring of a garage remote from the main house. We were told that whilst it was fine to link the swa to the MET the garage itself should have its own TT system, something to do with an "exported earth". This, apparantly, was outside the scope of the course and no further explanation was forthcoming. Could anyone explain exactly what is meant by this?
Not aiming this remark at SparkyMarky, but this shows how poor these 3 or 5 day wonder courses are. What are these so-called electricians meant to do when met with such a job ? As i had not been to college for a long, long time i sat one of these short courses, in 2003 before the start of part P. You had to prove your existing qualifications as an electrician before being allowed to enter as these were originally designed as refresher courses for the 16th update, not to make you an electrician.

 
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Exported earth..

here goes; basics first..

Why do we use "earth at all"?

There is protective & functional earthing.

protective earthing comprises source & electrical equipment earthing.

[functional earthing is for stuff like IT equipment with high leakage currents...but we will ignore them for today!]

quote from NICEIC..

"The purposes of source earthing are:

 
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