TT System Questions

[Engineer54]

Be my guest then ...lol!!

 

[trev]

I have their "regs" but the French is beyond me! Onto another TT myth then - is in true that in the "olden days" they would test how good an earth you had by connecting one side of a light bulb to live and the other side to the rod - the brighter the light the better the earth. I so want to try this!

You would be willing to hold a LAMP against an earthed rod then touch it with a live cable?
Do you promise to get your mates to post the video on youtube, there's a good chance you may be unable to

 

[UKMeterman]

Well..
In Canada I saw out in the country single wire HV with earth return....

 

[clicon357]

You would be willing to hold a LAMP against an earthed rod then touch it with a live cable?
Do you promise to get your mates to post the video on youtube, there's a good chance you may be unable to

It's on my bucket list!

 

[ackbarthestar]

I have their "regs" but the French is beyond me! Onto another TT myth then - is in true that in the "olden days" they would test how good an earth you had by connecting one side of a light bulb to live and the other side to the rod - the brighter the light the better the earth. I so want to try this!

Well, I believe there's a name for this - Live Working!

Try industrial insulated tongs, marigolds, wellies and a 11kV mat !

 

[Chr!s]

Not sure what your trying to prove with this link?? If it's driving 10 metres (several rods coupled) or more of earth rod in the ground, then as this link quite rightly points out, the good likelihood of those rods snapping or bending after hitting hard obstacles... (they won't be referring to 1.2m rods either, but 3m rods) Normally and as a matter of course, you would bore rather than drive (dependant of ground conditions) past 6 to 8 metres....

Chris, i've been involved with the creation of deep ground fields and other conventional and un- conventional grounding systems of deep and shallow earthing systems for a multitude of different purposes for over 30 years now. And in just about every type of soil condition i can think of, in different climates. I know what does work, and i also know what doesn't work, because i've had a few of them too in the early years. All i'm saying to you is, that relying on a bentonite slurry to be drawn in, as your driving a rod into the ground Won't and Can't work, for the reasons i've given you!! And probably why you were not too impressed with the results yourself...

Well i wasn't trying to prove anything as such, you said the use of Bentonite in the way i described was completely wrong. The method is used and it works to a degree, better than peeing on it LOL. The point i was making i suppose was that unless you are going to extreme measures soil consolidation will have the biggest effect on the Ra.

Even if you use Bentonite or marconite there's not going to be a massive reduction, roughly a 10 % reduction.

Take a soil resistivity uniform 120 ohms, 3 x 3 meter rod's, 1 rod 15mm diameter and another rod 50mm and 100mm using Bentonite.

The 15 rod comes out at 41 ohms, the 50mm rod comes out at 33 ohms and the 100mm at 29 ohms

So if we install 2 x 3 meter rods, 1 at 15mm and the other 100mm we have:

15mm = 24.6 ohms

100mm = 17.1 ohms

So as i said, if your driving in a few electrodes your not going to gain much by drilling 2 100mm holes and back filling, taking into account cost and time. Just add a little Bentonite as you drive this will help to over come soil consolidation and far less hassle. Your not going to gain much, but then you don't gain that much at 100mm lol.

Regards Chris

 

[Knobhead]

Onto another TT myth then - is in true that in the "olden days" they would test how good an earth you had by connecting one side of a light bulb to live and the other side to the rod - the brighter the light the better the earth. I so want to try this!

Done it, it works.
View attachment 9126
If you try it be careful.

 

[trev]

No dispute about whether it would work or not Tony, I just have visions of him in someone's garden with a pendant in one hand, a cable in the other and doing a little dance acting out a scene from The Green Mile

 

[alarm man]

Done it, it works.










If you try it be careful.

it does..

 

[Knobhead]

Where did you get that picture of me from? That was at school playing with a Van der Graaff generator or was it the Whimshurst machine.

 

[Engineer54]

Well i wasn't trying to prove anything as such, you said the use of Bentonite in the way i described was completely wrong. The method is used and it works to a degree, better than peeing on it LOL. The point i was making i suppose was that unless you are going to extreme measures soil consolidation will have the biggest effect on the Ra.

First off, it depends on what you mean by ''extreme measures'' if referring to a domestic installation yes i could agree, ...but it isn't considered so, in other applications. Oh, and anything is better than peeing on it!! lol!!...

As for Ra, No, not always!! I'm afraid you could be Wrong again, because that would depend very much on the resistivity of the soil type. Consolidation of an unfavourable soil type would make little difference to your Ra value, without a chemical or other form of enhancement. Consolidation by the way can be a lengthy process, anything from 18 mths to 5 years, again depending on ground/soil and climatic conditions (rainfall etc)


Even if you use Bentonite or marconite there's not going to be a massive reduction, roughly a 10 % reduction.

I have no idea, where you have got this 10% figure from, as it will be completely different for the type of ground/soil conditions. It can be significantly more than your stated 10% from my experience

Take a soil resistivity uniform 120 ohms, 3 x 3 meter rod's, 1 rod 15mm diameter and another rod 50mm and 100mm using Bentonite.

The 15 rod comes out at 41 ohms, the 50mm rod comes out at 33 ohms and the 100mm at 29 ohms

So if we install 2 x 3 meter rods, 1 at 15mm and the other 100mm we have:

15mm = 24.6 ohms

100mm = 17.1 ohms

If only designing an earthing system was as easy as this!!! ...lol!! Firstly, i've never seen or used an earth rod dia larger than 3/4''. Although i'm aware there are quite a few designer type earth electrodes available, but that's another matter!! Secondly while taking soil resistivity readings are an important factor, they are only giving you, if you like the top soil, soil resistivity values. If the ground type changes below, then so will your eventual Ra value. In reality a Topographic survey is also carried out on large or extensive earthing systems. Using a very similar basis to your calculation, i once in the past calculated an earth field, as to how many 2 X 2 rods positions i needed to get somewhere near the Ra value required. Only to find, that after having drilled all these bores, we achieved and surpassed that value with less than 2/3rds of the calculated bore holes. (i've never made that mistake again..lol!!)

The standard bore dia we use is 100mm so you can roughly say that the marconite will increase the rod dia to 100mm. It will also act as the medium of conductivity between the soil medium and the rod, ...No need to wait for consolidation, as the the marconite will fill the bore and to a certain extent, extend into the soil medium itself.

So as i said, if your driving in a few electrodes your not going to gain much by drilling 2 100mm holes and back filling, taking into account cost and time. Just add a little Bentonite as you drive this will help to over come soil consolidation and far less hassle. Your not going to gain much, but then you don't gain that much at 100mm lol.

Again, if talking about domestic, your correct!! But if i were you, i'd save the money your spending on the Bentonite, because that method is a pointless exercise and NO ...it still won't work!! You would find that you wiil achieve far better results by chemical enhancement in the situations you refer too. But ... if you did use bores holes, it would work, and probably work better than your 10% theory too!! lol!!!

Regards Chris

Let's face it, there are cut off points for everything in our industry, you plan/design systems etc, to the requirement of the installation. Same with roded earthing systems, your not going to install a 6m string of magnesium brick anodes to TT a domestic, but you would if you were protecting a very expensive and vital pipe line...

What i will say is, that TT systems today in the UK seems to have become a lost art, along with MICC and other proven wiring methods that now seem to be classed as ''Specialist Only'' lol!!

We could go on and on talking about the various methods, along with there advantages and disadvantages, as TT systems cover a vast area of uses and requirements, depending on it's situation. And that's before considering passive and active Cathodic Protection systems...lol!! So on this one, i think it's better to agree to disagree!! lol!!

 

[Chr!s]

Let's face it, there are cut off points for everything in our industry, you plan/design systems etc, to the requirement of the installation. Same with roded earthing systems, your not going to install a 6m string of magnesium brick anodes to TT a domestic, but you would if you were protecting a very expensive and vital pipe line...

What i will say is, that TT systems today in the UK seems to have become a lost art, along with MICC and other proven wiring methods that now seem to be classed as ''Specialist Only'' lol!!

We could go on and on talking about the various methods, along with there advantages and disadvantages, as TT systems cover a vast area of uses and requirements, depending on it's situation. And that's before considering passive and active Cathodic Protection systems...lol!! So on this one, i think it's better to agree to disagree!! lol!!

Well im not disagreeing with many of your points, and i am coming from a domestic small commercial direction where cost dictates to a degree.

Certainly on unfavorable soils, consolidation can take time i agree, though as i mentioned earlier on there is a place for soil enhancement without doubt, poor soils will require help.

The 10% comes from the manufacturers, though they do expect greater results, certainly where its used with a poor soil you would expect a far greater result than 10% than if you didn't.

Well when you talk about top soil to what depth? If you carry out a ground resistivity test, you can test the layers to a good depth, certainly below the top soil lol. Using the 4 pole tester and a Werner graph you can assess the ground resistivty at different levels, then you can calculate as you mention the different electrodes in that given soil. This gives you an approximation of the expected Ra.

Well 100mm will lower the Ra though it soon level's out after that. And certainly in poor soils there will be an improvement greater than the 10% and also enables an electrode to be less prone to seasonal variation.

Making a slurry, works to a degree, and you don't use too much, so cost is not an issue really, so its a good option for installations where cost is an issue. Voids will be created by the coupler and it will fill that void. Im not disagree 100mm bores are not a better option, cost does then come into play.

So i agree there's cut off levels and we have to install a Earthing system which is with in the balance of the client yet fit for the purpose.

Well i think it would be a good thread " Cathodic Protection", Galvanic and electrolytic cell corrosion, and the use of sacrificial anodes and impressed currents lol.

Regards Chris

 

[Knobhead]

Off you go then. But somehow I don't think there will be to many take up on it. Would be interesting though.

 

[Chr!s]

Off you go then. But somehow I don't think there will be to many take up on it. Would be interesting though.

I was sort of hoping you would tony

 

[La Poste]

Yeah don't stop here, this is the best thing I have read in ages.

Carry on chaps.