Earth electrode tester or not?

[D Skelton]

Trust me mate, if you've whacked in 2 x 1200 x 5/8" rods and you have a reading in the high hundreds as I have done many a time round here then it's gonna take a hell of a lot of work to bring that reading down to a sub ohm value!

 

[Outspoken]

How so? They both achieve exactly the same thing!

What makes people look daft to me is when they say a stable 10/20/30/40ohms is better than a stable 200ohms. Your 40ohms is just as useless as 200 of them!!!

WTF..did you read my posts FFS, Posts like that make you look a dick.

A resistance of 10Ω is clearly not doing the same as a resistance of 200Ω because the fault current will be higher (Do the ruddy maths and it will prove it)...now as I said in my posts you failed to read I did not say that this was an acceptable reading FFS, so take the earth rod out of your arse, remove the mega and PLEASE read what is said and not what you want it to say so you are all big and winning an argument..when we were not having one in the first place.

If you want my opinion on this, which I have refrained from giving in this thread then it is this...

BSI and the IET committee were wrong to state a 200Ω figure, it should have been 2Ω as a maximum for earth rods. However in my humble opinion any spark who does not achieve a reading, without good reason, of a maximum of 1Ω is failing in their moral responsibility to ensure that all fault currents are cleared effectively and disconnection times will always be compliant no matter what happens to the ground.

Pushing 4 or 5 rods into the ground is not real different from 2 rods, the regulations do not require a single earthing point, only that the earth paths do not overlap for adjacent rods.

I personally have driven five stacks of 4 rods into the ground around a structure to ensure that not only did it have adequate lightning protection but that the Zs reading was around 0.6Ω, and this was stable over many years.

If you investigate and price a job correctly then you should take into account the need to multiple rods, realistically a stack of 3 or 4 rods should meet the needs of the majority of installations to achieve a sub 1Ω Zs, but there is always an exception to the norm.

 

[Outspoken]

I would like to state the following to those who blindly follow the Regs.

While the publishers and the contributors believe that the information and the guidance given in this work is correct, all parties must rely upon their own skill and judgement when making use of it. Neither the publisher nor any contributor assume any liability to anyone for any loss or damage caused by an error or omission in the work, whether the error or omission is the result of negligence or any other cause. Any and all such liability is disclaimed.

Also:

Users are responsible for its correct application. Compliance with a British Standards cannot confer immunity from legal obligations.

You are responsible for all your work, the Regs are an absolute minimum standard but you are expected, nay, required, to exceed those standards and be professional at all times in how you undertake your works. If you do not agree with the Regs then may I suggest..

It is the constand aim of the IET and the BSI to improve the quality of our products and services. We should be grateful of anyone finding an inaccuracy or ambiguity while using this British Standard would inform the Secretary, G.D.Cronshaw (gcronshaw@----------), The IET, Six Hills Way, STEVENAGE, SG1 2AY, UK

 

[Engineer54]

That is the issue in essence....how is accepting Ra's of 10-15 ohms and not accepting 100-200 logical when in the next breath you are scorning reliance on RCD's?

Perfect analogy.

It's only a Perfect analogy, to those that can only see fit to twist and/or distort what has been clearly stated on this and other threads.

Still talking around Ra values, because you still can't, or rather don't want to see any other point or aspect except your own. There is absolutely nothing logical about accepting 100/200 ohms as being suitable for the vast majority of TT situations, extremely bad soil conditions would be an exception!! But baseing all TT installations on the lowest possible denominator, such as you seem to think is the way to go, is total nonsense!!

Yep, your right, i do scorn the reliance of RCD devices, and with very good reason!! Perhaps you might too, if you had seen the amount of boxes of RCD devices beeing returned for replacement on the projects i've been involved with, and more noticibly over the last 4 or 5 projects. And were not talking budget devices, but from so-called top of the range manufacturers!! I'm now fully expecting for you, to now come back and say, you have never had, seen or heard of an RCD to fail, ...Right?? lol!!

 

[Outspoken]

I'm with E54 on the RCD issue, personally I feel the reliance on them is a way to cover up for poor installation design and a lowering of overall standards. Don't get me wrong, used correctly I have no issue with them, but all too often, such as all socket circuits, they are abused and used in a poor way.

The main reason TT systems were required to have an RCD main switch was to abdicate the responsibility of the DNO to provide an adequate earth path that would ensure, at all times, that an installation met the requirements for disconnection times, and if you doubt this, then consider when the RCD requirement was introduced, about 18 months after the newly privatised DNO's commissioned a report that estimated the costs to ensure TT systems met the new requirements would cost them each tens of millions each year for about a decade.

Cynical, damn straight I am, it was corruption pure and simple, it started then and continues now. We need to return to properly designed, installed and verified installations that not only exceed the requirements of BS 7671:2008, but in effect begin the writing of a new standard so things are constantly improving and not being watered down for commercial interests of the big players and the DNO's.

 

[1Justin]

OK. On a more practical note, might I stand a chance of getting 5/8" (16mm) rod with a standard Makita 780W 2.9Kg hammer? - Or would I need to rent a big boy ?

 

[Outspoken]

OK. On a more practical note, might I stand a chance of getting 5/8" (16mm) rod with a standard Makita 780W 2.9Kg hammer? - Or would I need to rent a big boy ?

I have used a Makita 110V 780W hammer drill (on hammer stop obviously) for many years to drive in stakes. The ground resistance (physical not electrical) does determine how difficult this process is, but I have driven 4 5/8 rods into the ground with it...although I admit to finished off the last about half meter with a block of wood and sledge hammer!!

 

[1Justin]

Thanks, I'll remember the sledge as well then

 

[Engineer54]

No. It complies with the regs.If you go down the route of adding more rods how far do you go if it's not coming down to TN values,? if (say) 3 rods gets it to 15 ohms then you are no better off than you were before, so you have to keep going or you've wasted your time.
But I would advise the client of the safety advantages of a 100ma S type upstream of the 30ma on the domestic DB.

And say that the 3 Rods gave him a low single figure, he'd still be waisting his time would he??

As i keep saying, if your not prepared to make any effort whatsoever, your never going to know. And by the way, you'll be hard pressed NOT to improve on a value of 198 ohms obtained from rusting steel rods of unknown length!!

I do however, whole heatedly agree with the advice of fitting the upstream S type RCD....

 

[Engineer54]

WTF..did you read my posts FFS, Posts like that make you look a dick.

A resistance of 10Ω is clearly not doing the same as a resistance of 200Ω because the fault current will be higher (Do the ruddy maths and it will prove it)...now as I said in my posts you failed to read I did not say that this was an acceptable reading FFS, so take the earth rod out of your arse, remove the mega and PLEASE read what is said and not what you want it to say so you are all big and winning an argument..when we were not having one in the first place.

If you want my opinion on this, which I have refrained from giving in this thread then it is this...

BSI and the IET committee were wrong to state a 200Ω figure, it should have been 2Ω as a maximum for earth rods. However in my humble opinion any spark who does not achieve a reading, without good reason, of a maximum of 1Ω is failing in their moral responsibility to ensure that all fault currents are cleared effectively and disconnection times will always be compliant no matter what happens to the ground.

Pushing 4 or 5 rods into the ground is not real different from 2 rods, the regulations do not require a single earthing point, only that the earth paths do not overlap for adjacent rods.

I personally have driven five stacks of 4 rods into the ground around a structure to ensure that not only did it have adequate lightning protection but that the Zs reading was around 0.6Ω, and this was stable over many years.

If you investigate and price a job correctly then you should take into account the need to multiple rods, realistically a stack of 3 or 4 rods should meet the needs of the majority of installations to achieve a sub 1Ω Zs, but there is always an exception to the norm.

I'm afraid they only see what they want to see, and then twist and/or distort to suite they're position. The rest will be totally ignored, because it isn't in BS7671/OSG, that they steadfastly have to stand behind, as a way or an excuse of not having to do anything!!

 

[Outspoken]

I'm afraid they only see what they want to see, and then twist and/or distort to suite they're position. The rest will be totally ignored, because it isn't in BS7671/OSG, that they steadfastly have to stand behind, as a way or an excuse of not having to do anything!!

That is why I posted the comments from Page 2 where it states the legal onus is on us who are doing the works and the Regs are NOT an abdication of this responsibility and nor are they something to hide behind, they stand behind us as a back stop from which we are required to improve upon and not simply follow blindly.

 

[Engineer54]

OK. On a more practical note, might I stand a chance of getting 5/8" (16mm) rod with a standard Makita 780W 2.9Kg hammer? - Or would I need to rent a big boy ?

You'll need an SDS driver, which can be bought off the shelf, or you can make your own by welding a suitably sized socket (to fit the driving earth rod bolt) onto an old cut off SDS drill or similar. I have home made adaptors for both 5/8'' (that i haven't used to date) and 3/4'' rods.... Had them for more years than i care to remember too!! lol!! Off the shelf ones cost around the £20/25 mark....

 

[1Justin]

Nice idea, I'll dust the welder off and save a few quid.

 

[Engineer54]

Trust me mate, if you've whacked in 2 x 1200 x 5/8" rods and you have a reading in the high hundreds as I have done many a time round here then it's gonna take a hell of a lot of work to bring that reading down to a sub ohm value!

Were going round in circles again!! As i've already stated, if your dealing with extremely bad soil/ground conditions for a domestic installation, then i can fully agree with you that from a cost effective view, RCD's would be the way to go in most instances!! Not so, on say a medium sized commercial/industrial premises. As i have also said, i can substantially bring down the high values you talk about, and it won't be totally down to banging in rod after rod after rod.

 

[Marvo]

How so? They both achieve exactly the same thing!

What makes people look daft to me is when they say a stable 10/20/30/40ohms is better than a stable 200ohms. Your 40ohms is just as useless as 200 of them!!!

I've avoided this thread because I think the UK regs on acceptable TT rod impedances are unsatisfactory and putting all your eggs in one basket with RCD protection is not good practice but clearly the UK regs make provision for it so who would I be to preach any differently?

That said, given that as a UK electrician you're entitled to work to the value given so I can understand why you feel the 10/20/30/40ohms or 200 ohms makes no difference but I still disagree. I'd be more inclined to agree if the system earth's only function was to protect against overload currents and guarantee disconnection times .....but it isn't. The earth is functional also and especially nowadays with SMPS's, variable frequency motor controllers and surge arrestors it carries a considerable amount of standing leakage with a good possibility of a considerable amount more if certain power conditions occur. High earth impedances can adversely affect the functionality of devices and it can also encourage galvanic corrosion of pipework, hot water cylinders etc.


I'm happy to agree to disagree but I'm firmly in the camp of a low Ra being far better than a high one on any earthing arrangement including TT regardless of what's in the regs.

 

[Deleted member 9648]

I've avoided this thread because I think the UK regs on acceptable TT rod impedances are unsatisfactory and putting all your eggs in one basket with RCD protection is not good practice but clearly the UK regs make provision for it so who would I be to preach any differently?

That said, given that as a UK electrician you're entitled to work to the value given so I can understand why you feel the 10/20/30/40ohms or 200 ohms makes no difference but I still disagree. I'd be more inclined to agree if the system earth's only function was to protect against overload currents and guarantee disconnection times .....but it isn't. The earth is functional also and especially nowadays with SMPS's, variable frequency motor controllers and surge arrestors it carries a considerable amount of standing leakage with a good possibility of a considerable amount more if certain power conditions occur. High earth impedances can adversely affect the functionality of devices and it can also encourage galvanic corrosion of pipework, hot water cylinders etc.


I'm happy to agree to disagree but I'm firmly in the camp of a low Ra being far better than a high one on any earthing arrangement including TT regardless of what's in the regs.

I would agree completely where there are likely to be high earth leakage currents. However on the kind of small TT installs commonly queried on this forum that is not likely to be an issue.
The last TT I did was a shed/workshop fed off an ELCB with no SMPS's,variable frequency motor controllers and surge arrestors ,but plenty of lawnmowers and spades.

 

[Marvo]

I would agree completely where there are likely to be high earth leakage currents. However on the kind of small TT installs commonly queried on this forum that is not likely to be an issue.

Given the sheer number and type of modern appliances found in your average residence I'd argue the average household installation nowadays would qualify as an installation with considerable current flow in the earth. The problem with the functional earth current is it's an unknown quantity. Yes, you can measure the standing global leakage current of an installation easy enough but when power disturbances occur that standing leakage will increase by an unknown factor and along with a high impedance TT earth could quite possibly be sufficient to create a neutral earth voltage value that would be a concern or inadequate surge suppression that would be detrimental to electronic appliances.

 

[D Skelton]

WTF..did you read my posts FFS, Posts like that make you look a dick.

so take the earth rod out of your arse, remove the mega and PLEASE read what is said and not what you want it to say so you are all big and winning an argument..when we were not having one in the first place.

And this is where your side of the argument ceases to hold any credability at all. That's me done I think.

 

[Outspoken]

And this is where your side of the argument ceases to hold any credability at all. That's me done I think.

I see, you're proven to be in error and you run off. I thought you liked controversy and argument, yet when you misrepresent what someone actually posts in a way to try to "score points" you do not like being called out on it.

 

[D Skelton]

Not so, on say a medium sized commercial/industrial premises.

And this is where we agree. Commercial/industrial/agricultural TTs I would be banging them in until I got TN values.