Exporting earth on TT system

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Can't remember if this was covered in the great exporting earth posts of a few weeks ago (seem to remember discussion related to PME mostly).

With a garage just 6 feet from house and about 20 feet from earth rod, would anyone bother putting in a seperate rod??? Seems pointless to me but.....

 

steptoe

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oh my my....

glad you're taking an interest tho.

depends on your situation,

BUT,

it may be a good idea to run an additional 10mm earth (equipotential bond) along with your submain.

TBH a little more specific info as regards the garage (installed equipment and water etc) would be beneficial.

:)

 

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That "Exported Earth" thread is well known, worldwide, Gents. :D

 

steptoe

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I did a 65m sub main on a TT system a while back, I contacted NIC help line for advice on the earthing arrangements and they said second rod for sub DB and drop the earth on the feeder (sub DB end).
that would be due to differential in relative earth over that sort of distance Noz, you could prob find a 10 or 15v difference between actual earth and exported earth over that sort of distance, and thats not taking into account the difference in ground type.

you would need to run a stupid size main equipotential bond to probably.

 
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oh my my....glad you're taking an interest tho.

depends on your situation,

BUT,

it may be a good idea to run an additional 10mm earth (equipotential bond) along with your submain.

TBH a little more specific info as regards the garage (installed equipment and water etc) would be beneficial.

:)
Sounds good, as there is water in the garage. Will run in 6mm though, as if I remember rightly that is an adequate size for TT.

 

steptoe

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Sounds good, as there is water in the garage. Will run in 6mm though, as if I remember rightly that is an adequate size for TT.
6mm will be more than enough, how big is your Neutral tail? have you done a voltage drop calc for PFC? and also for Ze?

do you think the fault on the 6mm will never exceed the current your neighbour will put back through your water main?

these things will all come to you in a court of law, that is why I always say 10mm, you have 'taken all reasonable precautions' , 6mm will be laughed at in court, and you will save how many pounds?

 
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If 6mm is legal, its legal - havn't double checked yet but will before doing job. I suppose if system was ever upgraded to PME then it would have to be 10mm. (Can't quite undesratnd how fault from neighbour would shoot up water main, it being buried in earth I would expect it to dissipate to ground). But your right about not having to worry if exceeding cable sizes, and I found a drum of 10mm buried in my van yesterday that I had forgotten about, so will use that. After all, there's no point in asking advice if not prepared to listen :)

 

steptoe

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If 6mm is legal, its legal - havn't double checked yet but will before doing job. I suppose if system was ever upgraded to PME then it would have to be 10mm. (Can't quite undesratnd how fault from neighbour would shoot up water main, it being buried in earth I would expect it to dissipate to ground). But your right about not having to worry if exceeding cable sizes, and I found a drum of 10mm buried in my van yesterday that I had forgotten about, so will use that. After all, there's no point in asking advice if not prepared to listen :)
sorry, sometimes I just go overboard a bit sometimes. Blushing

you can get away with 2.5mm sometimes(still in 17th?) if in galv conduit or similar.

if your neighbour has PME then you can pull their fault in through your bonding, thats why its so large, and I just tend to work on the basis of everything going wrong if it can, Pray

remember, the guidance given in BS7671 is not legal. tho it can be used in a court of law to help show compliance with EAWR.

 

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and I just tend to work on the basis of everything going wrong if it can, Pray
Which, In My Humble Opinion - Is the BEST way to work it! ;)

 
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Which, In My Humble Opinion - Is the BEST way to work it! ;)
Yeah but, no but, yeah but, no. Having been trained and responsible for Health and Safety at several 'blue chip' organisations, the magic phrase in H&S legislation is 'reasonably practicable'. ie you are allowed to apply common sense to different circumstances, otherwise nothing would ever happen or cost too much to do. After all, to be perfectly safe from electricity, you wouldn't allow the public to use it at all.

I take the stance that I'm only working on one property and can only control that one installation, some clever bods in offices/ laboratories have worked out all the ins and outs of domestic electrics and written the regs accordingly and no doubt from 'fail safe' position. Therefore if I comply with regs on my work, I do not need to consider the neighbours or lightning strikes or anything else. :OPray:)

 

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Morning Matt Lucas, That's a valid way of looking at it too. :D

 
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I have also written safety stuff, and if you think 10 is safe, then 12 is safer and covers ones posterior nicely. For instance, when designing a winch for a crane type arrangement, the factor of safety is 5. ie the winch and associated components are 5 times stronger than they need to be to lift a nominated weight. Likewise I once calculated the main earth for a TT installation could be 0.25mm, but had to use 6mm minimum.

 

steptoe

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Yeah but, no but, yeah but, no. Having been trained and responsible for Health and Safety at several 'blue chip' organisations, the magic phrase in H&S legislation is 'reasonably practicable'. ie you are allowed to apply common sense to different circumstances, otherwise nothing would ever happen or cost too much to do. After all, to be perfectly safe from electricity, you wouldn't allow the public to use it at all.I take the stance that I'm only working on one property and can only control that one installation, some clever bods in offices/ laboratories have worked out all the ins and outs of domestic electrics and written the regs accordingly and no doubt from 'fail safe' position. Therefore if I comply with regs on my work, I do not need to consider the neighbours or lightning strikes or anything else. :OPray:)
I think you will find that you can NEVER use that arguement for the safety of an electrical installation.

do you have a copy of EAWR? (it is in there.) it is the ONLY regs you MUST work to and it IS STATUTORY, unlike 7671 which is only guidance.

cost is never a factor in electrical safety,

as far as is reasonable practical, well that is covered in section 16 of EAWR also,

remember, its your ass on the line when it goes to court.

it is actually illegal to instal an electricity consuming system WITHOUT taking into consideration other users of the network, (have at look at your providers T&C) so you MUST take into consideration your neighbours installation as well as your own.

lightning is also well covered in the regs as well, although perhaps if you do mainly domestic you may not have come across the preventative measures yet, but the regs are there for it.

 

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Steps, it's the Electricity at Work Act not 'Regs' which is what makes it a law. Only Act's that are passed by Parliament are enshrined in the law books. :)

 

steptoe

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Steps, it's the Electricity at Work Act not 'Regs' which is what makes it a law. Only Act's that are passed by Parliament are enshrined in the law books. :)
thank you Mr S for pointing out the blindingly obvious to me which I couldnt see cos of my own stoopidity there.

well, I hope my point got understood anyway.

just that people think if they do something to BS7671 then they will be absolved of all liability, which couldnt be further from the truth.

 

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Just that people think if they do something to BS7671 then they will be absolved of all liability, which couldn't be further from the truth.
Very true words Steps. Guiness Drink

 
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just that people think if they do something to BS7671 then they will be absolved of all liability, which couldnt be further from the truth.
No liability is liabilty, which is what we take on every time we start a job, and hence should be charging for.

What I was trying to get at is that cost is always an issue even to the people who write the regs / legislation in the first place. And to cover their liability they tend to over state what is required to cover all possible likely events around the country, hence most of the standards tend to over state what is actually required as a catch all/ cover all, fall back position. Therefore compliance with regs is all that is needed and not adding to them eg using 10mm cable when 6mm is sufficient.

Hope I've made that clearer, I did type the previous post whilst half asleep:z

Now I'm typ[ing after a few of these Guiness Drink :) before going back to :z

 
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