TT System Questions

[UKMeterman]

I did see TWO NERs in the 33 - 11 kV sub at the university...

 

[Engineer54]

We perhaps older guy's know there are several methods of creating a decent TT system!! The problem is, the younger sparks, ...that just seem to be playing at creating TT systems, because they know no different.

....What are you and other lecturers teaching these new students of today at collage, about providing a functional TT system?? As far as i can see, there being taught to totally rely on a RCD device for there earth fault protection, and only need one of these pointless 1-2m 3/8'' rods, that can't be extended even if you wanted
too.

The problem with your suggestion, is that you would need to drill a 50 to 75mm bore, that you can fill with the conductive cement, or bentonite mortar. Not particually cost effective on a domestic installation, as it would involve the hire off the drill and rig. Personally, i would consider 3m as the minimum depth, but 2 X 1.2m rods is i suppose better than One rod!!

 

[Chr!s]

I think the opinion is that at depths beyond 1.5m are not prone to seasonal variation, Certainly in this country.

Bentonite is a gel/slurry, create a pool and drive in your rod, it will pull the bentonite down, it will help a little but not much. Time is the best, the soil will consolidate over time reducing the Ra the most.

Marconite is an aggregate added to cement to create a conductive cement, costly as E54 has mention, cheaper to add several rods. Though in hard ground it does have its place.

I'd just couple 2 5/8 rods 1.2 or 1.5 long. This will put a minimum of 1 m out of the reach of seasonal variation. But as a minimum add at least one other, i tend to try and connect an electrode at every DB, along with extraneous conductive parts this soon reduces the Ra.

Just to add, a rule of thumb for parallel rod resistance percentage improvement.

Second rod 60%
Third rod 45%
Fourth rod 35%

Regards Chris

 

[Engineer54]

I think the opinion is that at depths beyond 1.5m are not prone to seasonal variation, Certainly in this country.

Bentonite is a gel/slurry, create a pool and drive in your rod, it will pull the bentonite down, it will help a little but not much. Time is the best, the soil will consolidate over time reducing the Ra the most.

Your description of Bentonite is completely wrong Chris, Firstly you do not just create a pool and have the earth rod take the slurry with it.... that would be a complete waste of time and of the bentonite. Who on earth taught you that method??

Secondly Bentonite is a recognised throughout the industry as a working enhancement of earthing electrodes and as such a proven system. Your description of '' it will help a little but not much'' is totally incorrect. Maybe in the installation method that you propose, but certainly not, when used correctly!! ie, ...in a bore or in a excavated trench etc!!
Used correctly Bentonite will fulfill it's function of substanually reducing the resistivity of the surrounding soil for probably the life of the installation, as it will continually absorb water/moisture and hold that moisture, it's also in it's own right, a conductive medium.

As for the other points you brought up in your post, ...Well there certainly better than most of the TT systems that you'll find in the UK, ...that's for sure!! lol!!

Depth equals stability first and reduction of Ra values secondly. Both are important factors in creating a ''Functional'' TT system....

 

[Chr!s]

Your description of Bentonite is completely wrong Chris, Firstly you do not just create a pool and have the earth rod take the slurry with it.... that would be a complete waste of time and of the bentonite. Who on earth taught you that method??

Well, it's a method i've used, suggested by several chartered engineers who work for two of the largest Earthing solutions company's in the UK. where drilling and back filling with Bentonite would be to costly/time consuming. As i said create a pool and drive in the rod keep pouring the mixture and this will be drawn down with the rod, this will fill most voids around the rod and lower its resistance. Jobs a good un

Secondly Bentonite is a recognised throughout the industry as a working enhancement of earthing electrodes and as such a proven system. Your description of '' it will help a little but not much'' is totally incorrect. Maybe in the installation method that you propose, but certainly not, when used correctly!! ie, ...in a bore or in a excavated trench etc!!
Used correctly Bentonite will fulfill it's function of substanually reducing the resistivity of the surrounding soil for probably the life of the installation, as it will continually absorb water/moisture and hold that moisture, it's also in it's own right, a conductive medium.

Not disagreeing if used as a back fill, though there is a limit om the radius and its effectiveness. Though certainly in many domestic situations i don't see many drilling holes LOL. The method i mention is relatively effective without to much hassle. Though i would probably use Marconite if i was trenching, it doesn't rely on water, Bentonite can dry out.

As for the other points you brought up in your post, ...Well there certainly better than most of the TT systems that you'll find in the UK, ...that's for sure!! lol!!

Depth equals stability first and reduction of Ra values secondly. Both are important factors in creating a ''Functional'' TT system....

Regards Chris

 

[Engineer54]

Tell me the name of this earthing solutions company, ....i'd love to talk to these C'eng's on this utterly useless application method of bentonite...lol!! The slurry would have to be so thin and therefore weak in bentonite content to even be drawn down with the rod!! For bentonite to be an effective enhancer, there needs to be a volume of the mixture surrounding the rod for it's full length in the soil. Having bits here and bits there, that would be so thin, it'll useless and probably dry out in next to no time!!

Check with any of the manufacturers of bentonite powder or granules and see what they say is the standard installation method!! You'll find that it is exactly the same as the Maronite method. Powdered bentonite being favoured for bores and granules for excavated trenches...

 

[Chr!s]

Tell me the name of this earthing solutions company, ....i'd love to talk to these C'eng's on this utterly useless application method of bentonite...lol!! The slurry would have to be so thin and therefore weak in bentonite content to even be drawn down with the rod!! For bentonite to be an effective enhancer, there needs to be a volume of the mixture surrounding the rod for it's full length in the soil. Having bits here and bits there, that would be so thin, it'll useless and probably dry out in next to no time!!

Check with any of the manufacturers of bentonite powder or granules and see what they say is the standard installation method!! You'll find that it is exactly the same as the Maronite method. Powdered bentonite being favoured for bores and granules for excavated trenches...

Well i think you need to consider when your driving several rods at depth the void left by the coupler will allow sufficient amounts of Bentonite to be drawn in. Once the gel begins to swell this will create a good contact with the rod where a void made by the coupler would of existed.

As for the Ceng, im not going to disagree with their techniques, im happy with it, it works to a degree. I can assure you they know there stuff Lol.

Regards Chris

 

[Chr!s]

E54, consider if you were being really adventurous and went for 10 meters depth with a power hammer, the void left by the couplers would be considerable. Its one way of over coming soil consolidation.

Regards Chris

 

[Engineer54]

I considered it for about 5 seconds flat Chris, commonsense and experience tells me there is not going to be any significant volume of bentonite surrounding a driven rod(s) of any depth. The Fact is, ....the minimum bore hole required for a bentonite enhanced earth rod is 50mm, the standard bore hole is 100mm, ...So you tell me how a thin slither of bentonite around a rod is going to do anything to enhance it's surface area and lower it's resistivity volume?? ...It can't, can it!!!!

If these Engineers advocate this method of installation for a bentonite slurry/mortar, then i would have good reason to doubt the term given to them in that ''They Know There Stuff' because clearly they Don't!!! ...It won't and can't work!!

 

[Engineer54]

E54, consider if you were being really adventurous and went for 10 meters depth with a power hammer, the void left by the couplers would be considerable. Its one way of over coming soil consolidation.

Regards Chris

The problem with that analogy is that you were not talking about 10metres in your original post you were talking 2 metres!! But even so, even driving 10 metres you are not going to end up with a bore of 50mm or more!! Not that anyone would consider driving 9 or 10 rods into the ground. Perhaps this is why you were not impressed with the results of bentonite, and why what went into the ground didn't last very long??

Bentonite is a highly absorbing medium and will continually absorb moisture from rainfall etc. It holds it's moisture for considerable periods of time, so is even good for areas of low seasonal areas of rainfall.... But only IF and WHEN it has been used correctly. I'm not saying it's the best, it's not. .....Conductive cement or Marconite would fill that title, but it is the a good runner-up in this field!!!

 

[Chr!s]

DEEP EARTH GROUNDING VERSUS SHAL

http://www.copperinfo.co.uk/earthing/downloads/pub-119-earthing-practice.pdf Page 95 - 96

These are a few ive managed to dig out, im sure there is others, so im not the only one LOL.

Regards Chris

 

[Chr!s]

The problem with that analogy is that you were not talking about 10metres in your original post you were talking 2 metres!! But even so, even driving 10 metres you are not going to end up with a bore of 50mm or more!! Not that anyone would consider driving 9 or 10 rods into the ground. Perhaps this is why you were not impressed with the results of bentonite, and why what went into the ground didn't last very long??

Bentonite is a highly absorbing medium and will continually absorb moisture from rainfall etc. It holds it's moisture for considerable periods of time, so is even good for areas of low seasonal areas of rainfall.... But only IF and WHEN it has been used correctly. I'm not saying it's the best, it's not. .....Conductive cement or Marconite would fill that title, but it is the a good runner-up in this field!!!

Well, im not saying the method doesn't work, it does to a degree, you drive in 3 5,8 rods and you will be surprised how much gets drawn down and there's no doubt it improves the Ra. Its a case of is it necessary i suppose, the soil will consolidate over time.

 

[Engineer54]

DEEP EARTH GROUNDING VERSUS SHAL

http://www.copperinfo.co.uk/earthing/downloads/pub-119-earthing-practice.pdf Page 95 - 96

These are a few ive managed to dig out, im sure there is others, so im not the only one LOL.

Regards Chris

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...

 

[Engineer54]

Well, im not saying the method doesn't work, it does to a degree, you drive in 3 5,8 rods and you will be surprised how much gets drawn down and there's no doubt it improves the Ra. Its a case of is it necessary i suppose, the soil will consolidate over time.

An earthing system made up of earth electrodes is installed with a minimal expected lifespan of 30 years or more. So if as your saying in your original post, intimating your method wasn't giving lasting results, then clearly it ''Doesn't work'' does it??

 

[alarm man]

you can get a decent tt system with 2 rods driven into the ground,its what we do its in the regs we dont need trenches we dont need to drill for oil just to put a rod in,i think were over complicating matters here..

 

[Engineer54]

you can get a decent tt system with 2 rods driven into the ground,its what we do its in the regs we dont need trenches we dont need to drill for oil just to put a rod in,i think were over complicating matters here..

I don't think were talking about the easily achievable low standard of what's required in the Reg's here. But rather in the type and/or method of installing an enhanced earth rod Alarm Man.... But i'm pleased to hear that you couple your rods to get that bit of extra depth on installations. ..lol!!

 

[clicon357]

Is it France where they "insist" on an earth plate for domestic TT i.e. a large copper plate buried in a pit - or did I dream that?

 

[Engineer54]

Is it France where they "insist" on an earth plate for domestic TT i.e. a large copper plate buried in a pit - or did I dream that?

You dreampt it i think, but they do want a decent TT system at domestic installations.
But It can be by plate(s)/ rods(s) or tape, etc...

 

[alarm man]

I don't think were talking about the easily achievable low standard of what's required in the Reg's here. But rather in the type and/or method of installing an enhanced earth rod Alarm Man.... But i'm pleased to hear that you couple your rods to get that bit of extra depth on installations. ..lol!!

it worked e54,78 ohms,well within regs..lol,maybe you could discuss it on the iet forums,lol

 

[clicon357]

You dreampt it i think, but they do want a decent TT system at domestic installations.
But It can be by plate(s)/ rods(s) or tape, etc...

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!