TT...installing 5/8" rods

[GLENNSPARK]

well...here I am again...this time its installing a TT system utilising 2X 5/8" rods...with the connector..:


here is the necessary gear as laid out (the 20mm PVC conny isn`t in the pic)


these are the type of rods you need...no 3/8" twigs here (apart from in that bush behind maybe)


site is about 1 1/2 meters away from the house...thats the first one in..now to connect the second onto the first ....and carry on...


still some way to go...


get it brayed in....Robert my assistant uses the fork with a bit of tape to keep the rod steady


thats a length of 10mm CSA G/Y being pulled through a length of conny for main earthing (the conny was dropped into the ground)

Ze was OK at just over 15 ohms...had to change the 16th edition setup in the board...it was configured as a split load 10 & 2....dropped another RCD in it and did it 5 & 5
happy days...:biggrin:

 

[Deleted member 9648]

Posts @ Outspoken and Glennspark. Prefer no input from E54.

I am curious, and I am not knocking anyone here or their respective efforts, but a couple of questions;

1. Glennspark, did you take a reading from the ROB to a Test spike or from the rod to the earth point of the installation?
2. When installing rods does anyone actually test them correctly with a rod tester?
3. When doing the testing, does anyone actually have spare rods and joiners in case they need to go down deeper?
4. What is the minimum reading you would personally accept?

When I have ever installed rods personally, or been on a job where they were installed, I have ensured that they were tested properly as they were inserted into the ground and that more rods were added until the reading achieved was an absolute minimum of 10Ω, however I have never stopped as soon as I get this value, I will add rods until I get a stable return. Over the years I have found that about 4 rods will get you into the 1Ω range (+/-0.5Ω), and a fifth rod will easily achieve lower than 1Ω, and at these depths we are talking stable return paths.

As said, I am not having a go at the technique anyone uses, I will always attempt to get the reading as near to 1Ω as possible because I hate the idea of being reliant on the RCD, like all devices they fail and the ground state within about 2.5m of the surface is too impacted by the above surface environment, man made influences and the weather/climate.

iI you are achieving TN values of Ra then good onya. You are not happy to rely on an RCD and therefore insist on a reading which will make that possible. Personally I am happy to rely on an RCD for the small scale TT systems I install and therefore see no need for TN values,the reason being that in the 35 years I,ve been a spark I've yet to hear of an incident on a typical UK TT installation which would have been prevented with a lower Ra . My issue is with those who are not achieving TN values and yet scorn reliance on RCD's,when the values they quote as being aimed for still rely on an RCD.

1)measurement was taken as a Ze....the rod including any main earthing conductor (in this case 10meters of 10mm G/Y)

2)all my MFTs all have 2 wire, 3 wire and specific ground resistance ability...i need to get the test leads & spikes for this

3)In this case I was left with 2 rods...had it been one of my own jobs i would have certainly got three....as i have advised before in here

4)well....certainly not 200 ohms.....nor 100 ohms for that matter...lol....definately no more than 21....and then monitor it to see how much that drops...if not enough then send another rod in...but you really should be acheaving better than 21....

Glenn why 21?....why not go the whole way and get a TN value?....isnt 21 just a figure plucked out of the air the same as 200....or 100? And assuming you install a TT system are you really going back to site to 'monitor' it over a period of time? Why not just get it to sub 1 ohm and go home and forget it?

 

[GLENNSPARK]

Posts @ Outspoken and Glennspark. Prefer no input from E54.


iI you are achieving TN values of Ra then good onya. You are not happy to rely on an RCD and therefore insist on a reading which will make that possible. Personally I am happy to rely on an RCD for the small scale TT systems I install and therefore see no need for TN values,the reason being that in the 35 years I,ve been a spark I've yet to hear of an incident on a typical UK TT installation which would have been prevented with a lower Ra . My issue is with those who are not achieving TN values and yet scorn reliance on RCD's,when the values they quote as being aimed for still rely on an RCD.




Glenn why 21?....why not go the whole way and get a TN value?....isnt 21 just a figure plucked out of the air the same as 200....or 100? And assuming you install a TT system are you really going back to site to 'monitor' it over a period of time? Why not just get it to sub 1 ohm and go home and forget it?

bus as i have said...i will monitor it....and if it dont come down....then go for another rod....
its stability i`m trying to acheave....

 

[D Skelton]

I think everyone knows where I stand on this. For those who don't, either install as many rods as neccessary to achieve a stable TN value or rely on an RCD. There is no inbetween and anyone who bleats on about how they got 10ohms and that's how it should be done is a fool! Your 10 ohms is just as good as my 500ohms as we'll both more than likely be relying on an RCD rated at 30mA and a type-s on the distribution circuit.

That's my two pence anyway, I say no more other than to say WP, I'm with you buddy

 

[Engineer54]

Posts @ Outspoken and Glennspark. Prefer no input from E54.


Tough because your going to get it!!

My issue is with those who are not achieving TN values and yet scorn reliance on RCD's,when the values they quote as being aimed for still rely on an RCD.

My issue, is that you always come on to any TT thread, after the OP has asked a question or whatever, been told how to do the job properly, and you ridicule the whole thing! No-one is denying that in most cases RCD's will still be necessary in the majority of instances, but then even domestic TN installations require them these days. TT systems really need an additional S type up front to cover RCD reliance issues!! The problem with UK TT installations is the almost general acceptance of using 1.2m twigs as the earth electrodes, and there lies the problem, they can't provide an installation with any certainty of stability. Now, going back over your past inputs in to TT systems, your stance is, that stability is also a waste of time and effort, as is putting any effort into creating a low value TT system as a whole!!

Glenn why 21?....why not go the whole way and get a TN value?....isn't 21 just a figure plucked out of the air the same as 200....or 100? And assuming you install a TT system are you really going back to site to 'monitor' it over a period of time? Why not just get it to sub 1 ohm and go home and forget it?

No it's not actually, that's the minimum figure given for substations and the like, not that you'll ever see such a high value at any substation, none that i know of anyway!! I think he's already told you what he wants from his install, and that's system stability. In my opinion his two rods will give him a good degree of stability but three rods will ensure stability of his system and as an added bonus bring his Ra value down significantly too. Shame on him for for even trying, ...well in your book anyway!!

And as a final point, just because YOU haven't heard of an incident where lower Ra values wouldn't of made a difference, doesn't mean it doesn't or hasn't happened!!

 

[Knobhead]

Not aimed at anyone, WP.

 

[GLENNSPARK]

Not aimed at anyone, WP.

looks like it came from someone a bit `blue blooded` Tony

 

[Engineer54]

I think everyone knows where I stand on this. For those who don't, either install as many rods as neccessary to achieve a stable TN value or rely on an RCD. There is no inbetween and anyone who bleats on about how they got 10ohms and that's how it should be done is a fool! Your 10 ohms is just as good as my 500ohms as we'll both more than likely be relying on an RCD rated at 30mA and a type-s on the distribution circuit.

That's my two pence anyway, I say no more other than to say WP, I'm with you buddy

If you really believe that, then it's not us that is the fool!!

That's what buddy's are for!! lol!!

 

[Knobhead]

OK that was an intended insult.

I’ve only been industrial and the only domestic TT install I’ve done was my own house*.
0.65 Ώ for the earth nest in the back yard. Lower when I altered it (it went way beyond the back yard!)

With industrial MV/LV substation installs we would be looking for < 0.5 Ώ.
1 Ώ being the limit for solid MV/LV earth interconnection.
>1 Ώ <5 Ώ and we had to operate an isolated earth where two nests were needed. That never happened as we would sink bore holes if needed to lower the LV earth values to <1Ώ.

Victoria centre in Nottingham the then EMEB had to drill 30m bore holes to form a nest in the Bunter Sandstone to get a good reading (at 30m it would be well below the water table.)

* I was an apprentice and buying my first house. Anything you wanted that was scrap you could buy for a pittance. I demolished an 11KV substation, copper lattice earth mat £1-00! The best bit, the then electrical senior engineer arrived with all the companies gear to test it.

 

[Deleted member 9648]

There are clearly two totally opposite camps here.
My view is clearly the minority but I have some support from respected member Mr Skelton. I have also had support via PM from another respected member who understandably doesnt want to get involved in a slanging match with See you next tuesday who's above reply I havent bothered reading.
Based on that and the historic support by IQ,who sadly doesnt post much now,I know I'm not wrong,just take a different view.


Skelton summed it up nicely, get a stable TN value if you wont rely on RCD 's for ADS....,whats the point otherwise of a stable 10-15-21 ohms?.....if a reading of 50 ohms,or a 100 ohms is stable whats the difference?

 

[D Skelton]

If you really believe that, then it's not us that is the fool!!

50V/10ohms = 5A fault current. Will this trip an OCPD? No. Will this trip a type-s? Yes. Will this trip a 30mA RCD? Yes.

50V/500ohms = 100mA fault current. Will this trip an OCPD? No. Will this trip a type-s? Yes. Will this trip a 30mA RCD? Yes.

See my point? There aint no difference!

Eng, I respect your opinion, I just think it's wrong.

 

[Engineer54]

Dear oh dear oh dear, it seems that the importance of Stability on a TT system is clearly very misunderstood by some here!! Perhaps i can suggest that some reading is called for here.

I find It amusing that around 18 months ago, when i was advocating very similar measures to that of Outspoken, i was bombarded and ridiculed by the very same people, ....then it was filling a garden with copper!! Now it seems, all has changed and something to be applauded, even though they wouldn't ever contemplate doing anything like it themselves!! lol!! Well i'm all for going all out to achieve TN values, so is the other camp going to change their mind again now?? lol!!

I've been involved with TT systems for more years than i care to remember as well as passive cathodic protection systems using just about every type of electrodes and method you care to mention. Even my own house in Cyprus is a TT system (0.89ohm overall and still improving) There are many ways to achieve sub or very near 1 ohm values in most soil/ground conditions, with just two or three of your short 1.2m earth rods, but unfortunately for some, you need to put a little effort and some extra cash into achieving it!! Let's say you achieved a value of 1 or 2 ohms with 3 rods, would you or wouldn't you add another rod?? You see for me, that situation would be a no-brainer, but for the other camp it would be ...Why Bother i've got my 30mA RCD!!!


Basically i have no time for those that can't or don't want to be bothered, but always seem to find it necessary to ridicule those that are. The very fact that a TT system should be installed to provide a 30 year lifespan and are often still in place far longer, doesn't seem to mean anything to them either. No wonder standards in the UK overall, are falling at the rate they are. Makes you wonder why they even bother with installing a TT system at all, when they can rely on a RCD to cover their arse, .....well it was OK when i left it 5 years ago mate!!


And it's ME that's wrong!! I don't think so!!

 

[telectrix]

achieving TN values is good, think wirepuller and most other members will agree. point WP has been making is that if TT values are above 1 or 2 ohms, then they are not really any better than 100 ohms. as OCPDs will not provide adequate fault protection.

 

[Engineer54]

achieving TN values is good, think wirepuller and most other members will agree. point WP has been making is that if TT values are above 1 or 2 ohms, then they are not really any better than 100 ohms. as OCPDs will not provide adequate fault protection.

Read past threads Tel, pointless to use all that copper according to WP around 18 months ago. We all know the draw backs of too higher a Ra value, but were normally talking more about Stability issues when talking about installing two X 1.2m, which as a consequence, will also in many circumstances provide around a 10 ohm Ra value!! But then it seems that stability is also not worth worrying about either!! lol!!

1 or 2 ohms, or lower single figure values, will give a far better protection level than 100 ohms. May not disconnect some OCPD's in specified times, but will trip, unlike a RCD with a reliability problem....

This dispute is all about those that are prepared to put the effort in to providing a good TT system, and those that are just not!! What annoys me, is that the can't be arsed, then find the need to high jack threads and ridicule those that do want to make an effort to do a good job.

 

[Deleted member 9648]

achieving TN values is good, think wirepuller and most other members will agree. point WP has been making is that if TT values are above 1 or 2 ohms, then they are not really any better than 100 ohms. as OCPDs will not provide adequate fault protection.

That is exactly my point.
Having against my better judgement read post 86 let me respond by stating that yes,there was a time when I didnt think TN values were obtainable by normal rodding methods. If anyone cares to trawl through more recent posts though you will find that I have no quibble with those who wont accept an RCD as an earth fault device,and insist on TN values of Ra and go the extra mile to get them. Nobody who uses this forum regularly over time can fail to be influenced by other opinions and the wealth of experience on here,and I have seen that values of Ra in line with TN values are possibly obtainable. But for the few small scale TT projects I do (sheds/small construction site units etc) I dont think it is worth 'filling a garden with copper' to acheive it,I am happy to adopt the 7671 preferred method of earth fault protection...RCD's (411.5.2 (i) ) and not start banging in rod after rod after rod.
If post 86 is 'all for going all out to achieve TN values' why the f*** is he having an orgasm over 15 ohms in post 24?

While I have the utmost respect for Glennspark and Tel's opinions on this,(and I would have for E's if he wasnt such an arrogant ****) nothing and nobody will ever convince me that 15 ohms is to be applauded and 150 to be ridiculed. It doesnt stack up.Nobody will ever convince me either that stability is that important for 'non-TN readings'...(15 ohms? 21 ohms ffs?) or that the only way to achieve it is to go down halfway to australia.There are a number of regular clients of ours with long standing TT installations served by 4ft rods where we carry out regular maintenance/small installs ,and the readings never vary,summer or winter.

 

[Engineer54]

That is exactly my point.
Having against my better judgement read post 86 let me respond by stating that yes,there was a time when I didnt think TN values were obtainable by normal rodding methods. If anyone cares to trawl through more recent posts though you will find that I have no quibble with those who wont accept an RCD as an earth fault device,and insist on TN values of Ra and go the extra mile to get them. Nobody who uses this forum regularly over time can fail to be influenced by other opinions and the wealth of experience on here,and I have seen that values of Ra in line with TN values are possibly obtainable. But for the few small scale TT projects I do (sheds/small construction site units etc) I dont think it is worth 'filling a garden with copper' to acheive it,I am happy to adopt the 7671 preferred method of earth fault protection...RCD's (411.5.2 (i) ) and not start banging in rod after rod after rod.
If post 86 is 'all for going all out to achieve TN values' why the f*** is he having an orgasm over 15 ohms in post 24?

While I have the utmost respect for Glennspark and Tel's opinions on this,(and I would have for E's if he wasnt such an arrogant ****) nothing and nobody will ever convince me that 15 ohms is to be applauded and 150 to be ridiculed. It doesnt stack up.Nobody will ever convince me either that stability is that important for 'non-TN readings'...(15 ohms? 21 ohms ffs?) or that the only way to achieve it is to go down halfway to australia.There are a number of regular clients of ours with long standing TT installations served by 4ft rods where we carry out regular maintenance/small installs ,and the readings never vary,summer or winter.

Arrogance or lack of, it has nothing to do with it, my stance has been the same throughout!! You can swear all you like, but ridiculing those that want to do things properly or better, that you find pointless isn't helpful to anyone, end of!! No-one's trying to convince you of anything, it's up to you to do your own research, ...and no-one is particularly applauding or ridiculing 15ohm/150ohms, that's just you seeing what you want to see!! I don't see how driving two or three 1.2m rods is going halfway to Australia. If you've been in the industry for 35 years, you would know that 2.4m and 3.6m are basically the same as what used to be the Standard sized rods in the UK, and still are in most other countries!!

No ones having orgasms, that's just you trying to emphasize your less than clever ridicule!!

As for your statement on 4 foot rods (which are probably twigs), I don't believe a word of it, not unless you have somehow changed the law of physics, especially in the UK's seasonal weather conditions!! A 4' rod having a certain ohmic value in the height of summer, will not have the same or even near ohmic value in the height of a freezing winter with snow on the ground, ....and that is an electrical Fact!! And is why depth and stability is, and always has been key to any TT roded system....


You stick to your BS 7671 (411) and continue to do as little as possible, and leave others to do Better!!