Discuss TT and 'stability' in the Electrical Forum area at ElectriciansForums.net

Deleted member 9648

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"Fool!!!

So now your telling us not to even bother with ensuring ''Stability'' in a TT installation now are you??"

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The above was a response from E54 to a post of mine in another thread,now I'm not going to take issue with being insulted by his lordship as thats his style rather than have a proper adult discussion.
BUT....perhaps we can all input on this and if I can be shown the error of my ways I promise I'll go away and never ever get involved in a TT Ra 'discussion' again.

I'll ask this question.....What constitutes 'stability'. If you have an Ra of 20 ohms and it gets to 25 is that unacceptable to you?.....30?...40?....what?
Why,when we know that a 100ma S type RCD will operate within the requirements at an Ra of 500 ohms...and a 30ma @1667 ohms....is the Bs recommended max of 200 ohms unacceptable and why am I a fool for accepting it?....Why does a 200 ohms rod need to be stable when we know a dramatic increase in resistance will still work?

It seems to me that if you cant accept high Ra values and 'twigs'...(and most on here dont) then you have to achieve a low enough and guaranteed stable Ra to operate an OCPD....otherwise what is the point of stability?
Hopefully some of the regular and respected members on here (including E 54) will not be too bored with this subject to explain why I am so wrong and they are so right,because I simply dont get it, and I've been an electrician for 30 years.....(referring to small scale TT installs only....ie single dwellings/outbuildings etc)
 
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G

Guest55

Why ?
Because rcd's are an electronic device that can fail or cease to operate correctly , usually with no tell-tale or visable signs even to the skilled eye.
So the answer is good electrical design , paying particular attention to sound earthing , which in a TT installation means getting the Ra to as low a reading as possible so as to operate any opd quickly.
AS you know , bs7671 doesnt give any definate min or max resistance figures , and things would be more straightforward if they did to be honest , but its up do you what reading youre prepared to accept , but i know through experience that sub 30 ohms is achievable in most locations and would be considered a stable reading by most experts.
 
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sparks1973

biffs about on the mark here.....as has been said...RCDs can and do fail to operate....especially in the hands of unskilled/uninstructed persons not under supervision.....test quartely?...hmm?...i think not in many a household.....
 

HandySparks

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Why ?
paying particular attention to sound earthing , which in a TT installation means getting the Ra to as low a reading as possible so as to operate any opd quickly.
...........but i know through experience that sub 30 ohms is achievable in most locations and would be considered a stable reading by most experts.
OK, so which OPD will open quickly with an Ra of 30ohms?

ps, I quite agree that you need a reliable earth, but that doesn't necessarily mean stable TN-C-S type values (although if you can achieve this, great).
 

Deleted member 9648

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OK, so which OPD will open quickly with an Ra of 30ohms?

ps, I quite agree that you need a reliable earth, but that doesn't necessarily mean stable TN-C-S type values (although if you can achieve this, great).
Exactly!.....that is my gripe with this....those who insist that 30 ohms is good and mock higher values are just not thinking it through! If you cant accept the reliability of an RCD what use is 30 ohms!
I also take the point about a RELIABLE earth in the context of a TT,I think reliable and stable are two entirely different things. An Ra which fluctuted between 30 ohms and 300 ohms might be unstable but is still perfectly reliable on a system with a 100maS type up front and 30ma final circuit protection.
 

telectrix

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well, let's face it. unless you are going to achieve sub 1 ohm values, you are having to rely on the RCD/s for fault protection. i do agree with eng54 on his stance you should strive for as low as practicable and that a 100mA up front RCD is a good back up to the 30mA RCDs. i won't lose any sleep if i can't get below 100 ohms, though.
 

Richard Burns

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I would say that when driving a rod in you are looking for a low value because this would then indicate that there is a large surface area in good contact with an "earthy" material, usually permanently damp earth.
If you have a large surface area in good contact then you should have a stable value so long as the rod is driven deep enough to stay damp.


If you have a value of say 300ohms then based on the general earth resistivity and the size of the rod you could assume that only part of the rod is making good contact and if this is the case then shifting of the earth or drying could mean less contact and so an unstable value that could exceed your say 500ohms for a 100mA RCD.


Where the 200ohm value came from as a recommendation no idea, not much use if you have a 500mA RCD.


The actual value of the Ra (So long as it is below the trip limit) is, I agree, immaterial from an operational point of view since the RCD will still trip, however as an assessment of reliability a stable reading would give more confidence, since only a long term assessment can determine stability then you are back to having as low reading as achievable(!) being a reading that one in which you can believe is stable.
 
S

sparks1973

depth = stability here.....surface soil conditions can fluctuate wildly....so get them rods down deep....
 
S

sparks1973

I would say that when driving a rod in you are looking for a low value because this would then indicate that there is a large surface area in good contact with an "earthy" material, usually permanently damp earth.
If you have a large surface area in good contact then you should have a stable value so long as the rod is driven deep enough to stay damp.


If you have a value of say 300ohms then based on the general earth resistivity and the size of the rod you could assume that only part of the rod is making good contact and if this is the case then shifting of the earth or drying could mean less contact and so an unstable value that could exceed your say 500ohms for a 100mA RCD.


Where the 200ohm value came from as a recommendation no idea, not much use if you have a 500mA RCD.


The actual value of the Ra (So long as it is below the trip limit) is, I agree, immaterial from an operational point of view since the RCD will still trip, however as an assessment of reliability a stable reading would give more confidence, since only a long term assessment can determine stability then you are back to having as low reading as achievable(!) being a reading that one in which you can believe is stable.
i think the original concept of 200 ohms Ra Richard was taking into consideration fluctuating soil conditions....worst case scenario being upto 8 times 200 ohms...which of course is 1600....so less than the 50V/0.30=1667....
 

D Skelton

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explain why I am so wrong and they are so right
I don't think you are wrong at all. I posed this very question only about a month ago on here and no one has yet given a satisfactory answer.

My belief is that a 100mA S-Type should always be used for fire protection and as a backup should one of the 30mA RCDs fail. The only other way to ensure a perfectly safe TT system would be to establish an Ra value of less than 1 ohm, and not just a 1 ohm value, but a stable 1 ohm value!!! A near on impossibility in your typical domestic TT set up when taking into account the extra time and cost involved in hammering in ten or more 12ft rods!



i know through experience that sub 30 ohms is achievable in most locations and would be considered a stable reading by most experts.
I don't doubt this, however 30 ohms is just as useless as a thousand ohms?!?
 

PEG

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Because this issue of "reliability" concerning TT Ra values,it would be interesting to hear about readings that sparks on here have encountered during repeat visits/testing of TT supplied properties to see if variations have been noted specifically down to rod resistance flunctuations.We have probably all arrived at a TT system first time round and had issues (older infrequently maintained systems) but having obtained a satisfactory value,have subsequent tests revealed any variations? I know we've all got better things to do than set-up a data base of chronological Ra readings :yawn: but has anyone installed a rod,listed value and then returned 1,2 or 5 years later and noted a drastic change,not due to any other reason than ground conditions? ......my goodness i'm getting dull...!
 
E

Engineer54

The above was a response from E54 to a post of mine in another thread,now I'm not going to take issue with being insulted by his lordship as thats his style rather than have a proper adult discussion.
BUT....perhaps we can all input on this and if I can be shown the error of my ways I promise I'll go away and never ever get involved in a TT Ra 'discussion' again.
First off, the word ''Fool'' was the first thing that sprang to mind. (which may not have been appropriate) Basically because this is the second time you have given, what can only be described as irresponsible advice to those that may not know any different about TT systems. ( eg newly qualified inexperienced electricians and the hoards of Electrical Trainee's) ....The first being, if you get an Ra of 200 ohms or thereabouts the job's a good-un and no need to bother any further as it complies with a numbty clause in BS7671 that everyone seems to take as gospel....

In this case, your Now advocating that ''Stability'' of a TT system is not an issue to be concerned or worried about either. I'm sorry but anyone that's been in this industry for 30 years, should know that stability is at the very essence of a reliable TT system, be it Domestic, Commercial, or Industrial... Let me make myself even clearer, ...Reliable = Stability, which in turn = Depth of a made earth electrode. Anyone that believes, that one of these short thin twigs can give a TT system stability, reliability, or longevity is living on cloud cuckoo land to be totally honest... Two standard extendible 5/8'' coupled rods or a single 2.4m 5/8'' rod should be considered as the minimum requirement to achieve those ends for a domestic or small commercial installation... Installed correctly, it will give the client/customer both Stability/reliability coupled with a decent Ra value.

We have gone through all this before, many times. Relying on a single 30mA RCD device on a TT system is not particularly a good idea, backing those two single multi circuit RCD's up with a 100mA S type makes for a far safer installation. (which i know you also advocate) Unfortunately how many, of even those electricians on this forum would actually consider installing an up front S type RCD, or even a normal 100mA RCD as standard practice?? Not many i think!!!

So now we are relying on bonded services to lower the Zs of an installation, (which in all honesty you shouldn't be doing) which in turn, may or may not, give some form of earth fault protection to circuits. Chances are, at anything around that 200 ohm Ra, that'll be slim to none. But at a far lower Ra, combined with the installations service bondings, though not meeting disconnection times, will have/could have a decent enough chance of disconnecting a faulted circuit in the absence of a working RCD (faulty RCD)... Obviously, the lower the Ra value the better.

And this is the crust of the matter, ....You advising this ''Not to even bother attitude'' and the use of these twigs, that can't give an installation either a half decent Ra level or the reliability/stability/longevity, that a TT installation ultimately requires, is at best irresponsible!!

On Another Note...

I would go further than some of the posters here, and say that it is more than just possible to achieve far less than a 30 ohm Ra with the standard set-up i described above. There are all sorts of ways of enhancing the ground and/or giving a made electrode the best chance of low reliable Ra levels.

I'll state again, it's funny that when i came into this industry, the recognised Ra level of aim for a ground rod, was 10 ohms. (which was in practice, more often than not, far lower ) But then they weren't using these totally useless Twigs, it was 8 and 10 foot 5/8 / 3/4'' rods they were driving in the ground. But then, there wasn't any RCD's about in those day's.... Now we have this dangerous conception of using them as cover-all devices which in reality, they most certainly are Not!!
 

Deleted member 9648

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Thanks for the thorough and comprehensive explanation of your views E54, I completely respect your point of view, but would point out that if my point of view is irresponsible,then the 'guidance' in bs7671 is also irresponsible......I would take issue with the suggestion that my offering the requirements of bs7671 to those who ask on this forum is somehow dangerous.
 
E

Engineer54

Thanks for the thorough and comprehensive explanation of your views E54, I completely respect your point of view, but would point out that if my point of view is irresponsible,then the 'guidance' in bs7671 is also irresponsible......I would take issue with the suggestion that my offering the requirements of bs7671 to those who ask on this forum is somehow dangerous.
Wirepuller, You know only too well what i think of this section of BS7671, It needs to be completely revised into a section that can give Real guidance, on what a good reliable working TT system should consist of, and not based on the lowest possible denominators as it surely is now... I don't think I've stated your views are dangerous in the true sense of the word, just maybe blinkered by that dammed BS 7671 section covering TT systems... I can't think of another area, where we disagree to the point/level of being at such diagonally opposed stand points...

What i do take umbrage at, is while i try and give some encouragement to those struggling to create reliable working TT systems, (and i know i do sometimes go overboard...lol!!) You always seem to be there to undermine that encouragement, with your ''why even bother'' stance...

A question for you, ...Do you really consider for a domestic TT system installation, that my standard of two extendible coupled 5/8'' rods or a single 2.4m rod is excessive or over the top cost and labour wise??
 

Deleted member 9648

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Regarding your question....No...... I have used such rods on rare occasions when my usual 'twig' failed to achieve a reading below 200 ohms. The last time a month or two ago when doing a 'make safe' on a failed voelcb install with a L-E fault resulting in shocks off everything,if I recall an initial reading of 350 ohms was reduced to around 80 with two 5/8" parallell rods...(sandstone bed rock made depth difficult)....a temp 30ma RCD main switch and all was good until a necessary rewire takes place.
I dont have an issue with that at all.....I do take issue with those who mock the bs 7671 value and yet are happy with readings of 30-40 ohms.
You can say what you like....I will never ever be able to see the logic of that.
 
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1shortcircuit

This thread has been an eye opener for me especially as I rarely come into contact with TT systems. There are still a lot of homes in my area that do use this earthing system so it's only a matter of time before I stumble across this situation.

At the moment and before reading this thread my thoughts would be that so long as I can achieve below 200 ohms when testing then this would be satisfactory as it is the "Number" stated in the regs.

Now here is the concern and where my lack of experience comes into play, whilst I may get below 200 ohms on the day of testing I am not fully aware of what can happen to the soil and what detrimental effect it may have on the resistance figures once the soil around the rod becomes frozen or dried out.

The attitude does seem to be, whack in a rod and obtain resistance tests under 200 ohms, bang in a 30mA protective device that will cover each and every circuit and jobs a goodun.

On reading E54's posts I can fully understand the logic for driving two extended rods into the ground and aiming to achieve far lower results.

This is most definitely an area that I need to do more reading on before I get caught by the short n curlies.

What would be the action made against you if:-

You fit a twig and protect each and every circuit with 30mA protection, test results are recorded at 150 ohms on day of testing but then 3 years down the line we are hit by a massive drought and the rod becomes ineffective and due to the RCD not being tested (quarterly as stated on the sticker on the front of the clients consumer unit) a fault occurs and the client/member of the clients family is injured as a result?

I would say that the electrician has worked within the Regs and therefore cannot be held liable but what is the reality of something like this happening on a TT earthing system?

:thumbsup
 

topquark

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I think you've kind of answered your own question 1SC, you know there is a possibility of that scenario, what would you do to minimise it? Put another rod on. IE if the first/second rod you put in gives you an "acceptable" reading (to you as the professional) put another one on and drive in.
 

spark 68

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Hi 1SC,

Just a small point, the test button does not need an earth to operate, it operates by placing a resistor across the incoming line side to the out going neutral side artificially creating an imbalance, this only tests the electromechanical aspect of the RCD/RCBO.
 
E

Engineer54

Regarding your question....No...... I have used such rods on rare occasions when my usual 'twig' failed to achieve a reading below 200 ohms. The last time a month or two ago when doing a 'make safe' on a failed voelcb install with a L-E fault resulting in shocks off everything,if I recall an initial reading of 350 ohms was reduced to around 80 with two 5/8" parallell rods...(sandstone bed rock made depth difficult)....a temp 30ma RCD main switch and all was good until a necessary rewire takes place.
I dont have an issue with that at all.....I do take issue with those who mock the bs 7671 value and yet are happy with readings of 30-40 ohms.
You can say what you like....I will never ever be able to see the logic of that.
I can only restate, that with a lower Ra value you DO stand a better chance of disconnecting a faulted circuit or RCD. As i said, maybe not in the stipulated times, but a disconnection just the same. Yes you will be also relying on the bonding of services, to bring your Zs down in most circumstances, which is why placement of made electrodes is just as important as the depth and stability you afford to the electrode. Making sure that the position of the rod, is outside the influence of the incoming metallic services, will certainly be a big help in this respect. The problem here is, that you can't test for overlapping sphere's of influence without a dedicated earth tester. Most self employed electricians won't possess such test kit, using a loop tester to read Ra values. But a careful survey of where services enter the house or building can give the electrician a good idea of where not to position an earth rod. And using the rule of thumb separation rule, (one to two times the length of the driven rod) you can make a reasonable assessment as to where your rod is best placed.

As for your recent example, ...yes there are going to be times where you just cannot achieve suitable depths for rod placements without having to resort to bore drilling. But there are other means of made electrodes, but unfortunately all are going to be more expensive in material cost and labour to install, than driving a rod in the ground... But ALL will out perform to the enth degree, a short thin twig....

On a final note, If the BS value was a realistic value, and not taken from the lowest denominator, i might be able to a point, agree with you. But while it remains at this ridiculous and totally useless 200 ohm value (a mockery in itself), in all honesty, i can't!!
 
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1shortcircuit

Hi 1SC,

Just a small point, the test button does not need an earth to operate, it operates by placing a resistor across the incoming line side to the out going neutral side artificially creating an imbalance, this only tests the electromechanical aspect of the RCD/RCBO.
That I am aware of spark :thumbsup

It seems that 30mA RCD protection is being used as a fail safe option and by doing so the Earth resistance through rods is possibly given less attention which is the point that I believe E54 is making here?

We all know that a test button is rarely pushed and that these devices can become faulty or stick. If this was to be the case and there was a fault to earth, RCD fails and rod resistance has become unstable then where does that lead us? I think again this is why E54 states so clearly that more effort should be taken whilst carrying out this part of the installation process?

I think I understand both E54 and wirepullers comments but it's a shame to see such a disagreement between such valuable members.
 
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Engineer54

I think I understand both E54 and wirepullers comments but it's a shame to see such a disagreement between such valuable members.
It's just a storm in a Tea Cup shortcircuit!! ...lol!!!
 
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spark 68

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I agree 1SC,

I can see both sides of this argument, and neither side are wrong per se.

E54's argument is correct in that stability is the main factor (IMO), I would rather have a rod that gives an Ra of a 100 ohms but was deep enough to be stable and not fluctuate than a shallow rod that read 50 ohms that is likely to increase in the dry or frozen seasons.

The other posters are correct too, in that it does not really matter whether the rod measured 20 ohms or 200ohms, in the sense that neither will operate the OCPD device directly, and both will rely on the RCD to achieve disconnection.

As I said stability is the key here.

Incidentally, the 16th ed amd.1 OSG gives 220 ohms as the max recommended Ra, this OSG uses 230V as the Uo for the calcs.
So which edition Regs gave the lower 10 ohms figure E54 ?, I have seen this figure given for generators and the like, but not for general TT systems that used RCDs to achieve the disconnection times.
 
E

Engineer54

I agree 1SC,

I can see both sides of this argument, and neither side are wrong per se.

E54's argument is correct in that stability is the main factor (IMO), I would rather have a rod that gives an Ra of a 100 ohms but was deep enough to be stable and not fluctuate than a shallow rod that read 50 ohms that is likely to increase in the dry or frozen seasons.

The other posters are correct too, in that it does not really matter whether the rod measured 20 ohms or 200ohms, in the sense that neither will operate the OCPD device directly, and both will rely on the RCD to achieve disconnection.

As I said stability is the key here.

Incidentally, the 16th ed amd.1 OSG gives 220 ohms as the max recommended Ra, this OSG uses 230V as the Uo for the calcs.
So which edition Regs gave the lower 10 ohms figure E54 ?, I have seen this figure given for generators and the like, but not for general TT systems that used RCDs to achieve the disconnection times.
Long before the 16th edition, more like in the 13th edition times. Not even sure if it was mentioned in the reg's per say, but the 10 ohm value was pretty much standard throughout the industry for ''All'' TT type systems at that time, including lightning protection systems. ...Now that hasn't changed any, that's still a Max 10 ohms too, if i'm not mistaken....
 

spark 68

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Long before the 16th edition, more like in the 13th edition times. Not even sure if it was mentioned in the reg's per say, but the 10 ohm value was pretty much standard throughout the industry for ''All'' TT type systems at that time, including lightning protection systems. ...Now that hasn't changed any, that's still a Max 10 ohms too, if i'm not mistaken....
Thanks E54, it was a genuine question, it is not actually mentioned in the 16th ed reg books I have (amd1 &2) either, but is mentioned in the respective OSG's, I cannot find my 16th ed GN3, and I have no other GN's other than the two 17th edition sets.

I was just intrigued to where the figure came from.
 
I think these discussions and disagreements are the strength of the forum-without them we could just produce an FAQ based on BS7671 and be done with it ;)

As has been stated many times above, stability is the key and on that front, I agree with E54 on the 'twigs' thing.
I keep asking for any documented evidence of any injury or incident concerning a TT system with a failed RCD but there simply isn't any available because the system actually works in it's present form and has done for many years now. I think part of the reason for that might be the fact that although an RCD might fail an instrument test at say 5X IΔn, how many faults are actually of that low magnitude?

I often ramp test failed 30mA RCD/RCBO devices and it's quite surprising to see how many still trip around the 200-500mA range and virtually all on the way up to 1000mA.

For the record, I'd never say 'no need to bother trying for a lower Ra value' and neither as I recall has Wirepuller ever implied that but his point about the futility of hitting 30, 40 or 200 Ohm values of Ra is absolutely correct!
 

Deleted member 9648

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Thanks to all for the constructive comments rather than a slagging match..:smiley2:...as this is probably the only subject on which I have a major dispute with anyone on here it's something perhaps this thread has cleared up for me, and I'll try and leave it alone now...:8:.(cue big cheers)
Re post 16....I suppose you'd have to ask yourself if the 200 ohms is ever likely to get to 1667 ohms.....as it would need to get above that before you might have a problem with the Ra value affecting a 30ma RCD....(not advocating such high values as ok before anyone asks!)
 

Marvo

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Technical issues aside, the thing the surprises me is the the UK regs are happy to put all their eggs in one basket and rely solely on the functionality of the RCD when it comes to the acceptable TT figures whereas pretty much everywhere else in the regs there's a belt and braces approach wherever possible. I can't help wonder why this is the exception to the rule...
 
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Engineer54

Technical issues aside, the thing the surprises me is the the UK regs are happy to put all their eggs in one basket and rely solely on the functionality of the RCD when it comes to the acceptable TT figures whereas pretty much everywhere else in the regs there's a belt and braces approach wherever possible. I can't help wonder why this is the exception to the rule...
And like everywhere else in the world of any consequence, i'd be willing to wager a months salary, that your max Ra value isn't 200 ohms. ...lol!!! You also probably have a requirement for an up-front RCD, regardless of any downstream RCD devices being present??
 

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Technical issues aside, the thing the surprises me is the the UK regs are happy to put all their eggs in one basket and rely solely on the functionality of the RCD when it comes to the acceptable TT figures whereas pretty much everywhere else in the regs there's a belt and braces approach wherever possible. I can't help wonder why this is the exception to the rule...
Agree....As you know I have no issues with the preferred means on disconnection being an RCD (which allows high Ra values) but it is a mistake to allow a single RCD.....it should be a requirement for more than one device,ideally a 100ma S type main switch with 30ma to final circuits.
 
D

drew35

After reading all of these post it reminds me why I always try to get a PME supply put in by the DNO, then I've washed my hands of the responsibility, over to you DNO!
I do live in rural Wales though so have plenty of TT experience, and I've learnt that when it comes to solid slate they're best avoided!
There as always are difference's of opinion, and a lot of discussion, as to whether the BS7671 is correct in certain area's. But we have to remember that should somebody be hurt or killed by an electrical installation its the BS7671 that will be used to prosecute us. Whether we agree with it or not. And if its not followed then its porridge and water!
 
we have to remember that should somebody be hurt or killed by an electrical installation its the BS7671 that will be used to prosecute us. Whether we agree with it or not. And if its not followed then its porridge and water!
More like Playstations and university degrees mate:)
 
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Engineer54

One has to wonder why, that old 10 ohm value was ever dropped, as that value had been the norm for years, long before i came into the industry, (and it was taken as the MAX and not the cut-off point) and long before RCD's were even thought about. One can only assume, mainly because of the common use of RCD devices. Which is fine to a point. But still foolish to then totally rely on a single RCD for your earth fault protection throughout a complete installation. Then you have the advent of these non extendable short thin twigs to replace 8 and 10 foot rods, and you can see straight away, that things have gone drastically down hill in a relatively short period of time in the UK...

I don't and can't accept that because people haven't read of instances of injury or accident or whatever, in publications it has never happened. That would be to assume that every accident or occurrence would automatically be reported and investigated, which is simply never going to happen in the real world. When accepted electrical theory tells us, what will or can happen in the absence of a fully functional RCD device and an earth rod resistance that is so high as to be totally useless. So the present system only really works when the RCD device is functional, it won't and can't work when it isn't. We know that the chances of a broken neutral on a PME/TNC-S as being, to say the least, remote, ...but we still take precautions against that possibility!! So why is there a reluctance to accept taking similar steps with TT systems??....

At the end of the day, the more effort and application put into creating a functional and working TT system, the better that TT system will be. You don't have to necessarily go overboard, just careful positioning of the rod, or made electrode, ensuring to the best of your ability the electrodes overall stability, a little knowledge on ground and/or rod enhancement where required, and you won't go too far wrong!! You will not achieve any of this using 3/8'' short twigs or being satisfied with a 200 ohm or thereabouts Ra level.... And you can take that to the Bank!!!
 

Marvo

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Another spin-off of a high impedance earth that hasn't been mentioned is that it sets the scene for accelerated corrosion of copper pipework and hot water cylinders or immersion heaters etc. Whilst this may not be a direct electrical safety issue it would certainly be a consideration when coming up with a regulated acceptable figure.
 
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Engineer54

Another spin-off of a high impedance earth that hasn't been mentioned is that it sets the scene for accelerated corrosion of copper pipework and hot water cylinders or immersion heaters etc. Whilst this may not be a direct electrical safety issue it would certainly be a consideration when coming up with a regulated acceptable figure.
Marvo, Jessus, ...Don't go throwing them another spanner into their works!! lol!!! :rolleyes2:
 
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Engineer54

Think i should have posted this on a TT system thread instead of crimping tool thread, where i came across this bit of useful kit...lol!! Anyway i've done so now.... lol!!

How about this little bit of kit. With a bit of adapting to extend the drill bit(s) this could be a god send for TT system installations. Perfect for Bentonite and conductive mortar applications, or even part bored, part driven earth rods. The bored section backfilled with Bentonite, keeping the conductive moisture content constant for long periods of time....

Well worth having this bit of kit, if you do a fair amount of TT systems in your area... Plus, as a bonus, you can even do your own fence posts etc, as well as a few other things...lol!!!!

NEW GROUND HOLE DRILL 52CC | eBay


 
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Engineer54

I've seen one of those in use, well actually it was a lot larger but it was on that TV program (decked out or something) LETHAL bit of kit lol
No idea about UK TV channels and programmes these day's. lol!!

This bit of kit is not that too dissimilar, to those that are used professionally for drilling earth rod bores. Though certainly bigger and more powerful than this small hand unit... This units drill bit's just need extending by either welding or by threading modifications...
 
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sparks1973

After reading all of these post it reminds me why I always try to get a PME supply put in by the DNO, then I've washed my hands of the responsibility, over to you DNO!
I do live in rural Wales though so have plenty of TT experience, and I've learnt that when it comes to solid slate they're best avoided!
There as always are difference's of opinion, and a lot of discussion, as to whether the BS7671 is correct in certain area's. But we have to remember that should somebody be hurt or killed by an electrical installation its the BS7671 that will be used to prosecute us. Whether we agree with it or not. And if its not followed then its porridge and water!
BS7671 will be used to prosecute us eh?....don`t think so love...BS7671 can be used to show compliance with the leccy at work regs 1989...but thats all....BS7671 is a guidance note lass......and non-statutary n all.....EAWR1989 will be the one thats used in court.....
 
1

1shortcircuit

BS7671 will be used to prosecute us eh?....don`t think so love...BS7671 can be used to show compliance with the leccy at work regs 1989...but thats all....BS7671 is a guidance note lass......and non-statutary n all.....EAWR1989 will be the one thats used in court.....
The problem being, whilst you may be correct... The prosecutor will appoint someone who can tie you up in knots with the BS7671. IF you've not worked to the regs then you will have to explain why and defend that it complies with or is better than what BS7671 states.

Also, IIRC Building Regs, which IS LAW, states that all work must conform with BS7671 so you're in the deep if you don't really and why chance it?

I personally would not like to EVER be in that situation:thumbsup
 
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sparks1973

yeah well i know that working to one will/should demonstrate compliance with the other...but the point i was making is it will be the EAWR1989 that has the final say in court...not BS7671.....thats used to show compliance with EAWR.....
 

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