Very Hi ZS Reading on TT system? any advice

[srl-8]

Hi guys,

i have changed a fuse board today in a outbuilding/large shed (it has a kitchen and shower and lounge etc.. a )

It is a TT system with earth rod.

My ZE reading was 187 ohms - now the regs state I am ok upto 200, so I assumed this was ok.

All the R1 + R2 and insulation resistance came back normal.

When I carried out the ZS tests, the reading were very high, for example:

Shower circuit on a 40a MCB - 2.6 omhs !
Kitchen Ring on a 32a mcb - 2.7 omhs !

same for lounge and bedroom rings.

I have checked to regs and these figures are over the maximum allowed.


Any advice ???

 

[Rockingit]

That's what all the girls say, can't beat a bit of length.

 

[IQ Electrical]

so why do we keep seeing these shallow rods ....all connected in series...as if thats gonna do owt..lol.....

Rods are available in a few lengths to suit a variety of applications, there could be cases where a rock shelf prevents good depth so multiple rods have to be used, not ideal but it does happen, you are also not just restricted to rods as an electrode...

 

[Engineer54]

There's far more fiction here than there ever was in War & Peace, I back up my arguments with all available statistics, British Standards and years of experience installing perfectly safe TT installations that meet the requirements of those standards.

Of course, the requirements are guided minima and if anyone wants to fill up a garden with copper to slavishly attempt to attain Ra values akin to a TN system then go for it but at least ponder beforehand the futility and costs of the task!

So where's the fiction?? You back up your arguments with ''Statistics'' haha!!! Who's statistics?? have you never heard that old saying about Statistic's, it basically tell's you Never to trust statistic's and for very good reason. The very same figures, can be made to say anything the authour wants them to say, ....An that's a well proven ''Fact!!''

Are you really trying to convince me that a 1m rod with a Ra of 200ohms is and will remain safe for the duration of it's lifespan, even when the paralleled bonding pipes are replaced with plastic services?? Come on IQ pull the other leg, it's got bigger bells on!!

Now, no-one is saying you should slavishly attempt to obtain TN values from a TT system, or filling a garden with copper, that's twisting what i have said here, they are Your words trying to be clever, NOT mine!! What i will say is, in generally found garden British soils, i could in most circumstances achieve a below 10ohm Ra with a maximum of 2 twin rod positions. If that is filling a garden with copper, so be it ...lol!!
What i'm also saying is, Not even trying to improve, a crap Ra value with a deeper rod, or at a second location, to me doesn't say much for an electrician that's installing/creating a TT system. Also a bad Standard, is a bad Standard, whatever way you like to dress it!!

If you have, with your years of experience, installed TT systems that are anything like those that seem to be the norm these days in the UK, ie, a single 1m rod with an Ra of around the 200 ohm mark, i'm sorry, your fooling yourself big time, thinking that's perfectly safe!! That would only be safe as such, while a the prime protection RCD was functional... It sure ain't gonna be safe when it isn't functional!!!

The only way i would feel even half happy leaving such a TT system in place, is if the CU in question, had an up-front 100mA S type RCD and all the circuit protective devices were RCBO's. At least then you have 2 RCD devices covering your bum, unlikely that both will fail, but then again, it's not unheard of either...

 

[IQ Electrical]

Back to the 1M rod again, where did that suggestion come from? (certainly not me!).

 

[Engineer54]

You'd need some depth to get to TN values in most UK soils!

I'd take a 400 Ohm Ra reading on a 2.4M rod anytime rather than 50 Ohms on a 1M rod though, depth is indeed king!

E54 keeps mentioning this 1M rod as if that's all anyone here uses!

That's right, would you like to put any money on this one IQ, i've been looking at several well known wholesalers in the UK, and that is the ONLY length they stock, be they 3/8'' or 5/8'' !! I haven't seen one, that stocks 3/4'' rods of any length!!

So that's exactly what everyone is using, unless they are purchasing direct from people like Furse!!!

 

[Deleted member 9648]

I have installed and inspected many small-medium TT systems in the south east UK over the 30+ years I have been in the trade.Most of those have utilised 1m rods.Off the top of my head I cant recall an Ra greater than about 250 ohms on an existing at any time of the year. Last year I did a temporary site hut install on the north downs...(chalk)...in the height of summer on very dry ground and got an Ra of around 350 ohms with a single rod. Linking two 1m rods got it down to around 120 ohms...more than acceptable.
Given that 30ma RCD protection was provided, in practice the 350 ohms Ra would have provided satisfactory earth fault protection even though it exceeded the UK recommended maximum.
No doubt E54 will be appalled and call me everything from incompetant to downright dangerous. But like IQ,I have never heard of an incident on a UK TT which could be attributed to a UK TT Ra which would have been prevented by an Ra of the level E54 advocates.
For that reason I am content to adhere to Bs 7671 requirements for TT systems,and have no doubts over the safety of such systems.
It is my belief that E54's posts on Ra values are misleading to those who seek advise on TT requirements...which is why I continue to open this particular can of worms.

 

[GLENNSPARK]

Rods are available in a few lengths to suit a variety of applications, there could be cases where a rock shelf prevents good depth so multiple rods have to be used, not ideal but it does happen, you are also not just restricted to rods as an electrode...

i agree that there are other means of earthing (tt) than rods ...such as tape/s and/or plate/s....

 

[IQ Electrical]

That's right, would you like to put any money on this one IQ, i've been looking at several well known wholesalers in the UK, and that is the ONLY length they stock, be they 3/8'' or 5/8'' !! I haven't seen one, that stocks 3/4'' rods of any length!!

So that's exactly what everyone is using, unless they are purchasing direct from people like Furse!!!

Do they not also sell a coupler that fits the 1.2M rod giving at X2 the 2.4M that I mentioned a few posts back?

 

[Engineer54]

Haha, the last person i need to teach me how to get a TT system to protect an installation, or how to create a TT system is you!! If anyone is misleading anyone here on Ra values and stability it's those that advocate BS7671!! You open these can of worms, because you are satisfied with an inadequate system based on an inadequate section in the BS7671 that has been in need of revision for too long..

Frankly i don't give a dam what you are prepared to walk away from on a TT system, but instructing those that are inexperienced, to ignore sound advice to improve a crap Ra value based on what is a nonsense Ra value because you happen to be happy with it, beggars belief!! As i thought you use 1m rods like everyone else and even after all these years of experience ,still actually believe what you have installed is a good, stable and reliable TT system,. ....NO Comment!!!

 

[Engineer54]

Do they not also sell a coupler that fits the 1.2M rod giving at X2 the 2.4M that I mentioned a few posts back?

Come on now, and just how many actually buy those couplers or come to that, the second rod... NO need IQ, ...they only need 200 ohms ...and what's stability all about, when it's at home, do we really need it .... It rarely happens, and You know it doesn't!!!

 

[JONOXNAM]

Come on now, and just how many actually buy those couplers or come to that, the second rod... NO need IQ, ...they only need 200 ohms ...and what's stability all about, when it's at home, do we really need it .... It rarely happens, and You know it doesn't!!!

I would just ask one Q for all the people who believe the regs values are the end of... if we switch to I/R - would you walk away from a dwelling if the I/R was 2.0Mohm?

The regs values are the as a min safety values....

 

[IQ Electrical]

Come on now, and just how many actually buy those couplers or come to that, the second rod... NO need IQ, ...they only need 200 ohms ...and what's stability all about, when it's at home, do we really need it .... It rarely happens, and You know it doesn't!!!

I wish you'd been invited to the Guidance Note 3 Amendment panel that I attended, if you'd produced all the evidence and research to back up your argument (none) then we could have revised this lethal 200 Ohm figure and saved countless lives in the process.

Until then I'll just continue with my reckless adherence to all published guidance on the subject.

 

[GLENNSPARK]

I would just ask one Q for all the people who believe the regs values are the end of... if we switch to I/R - would you walk away from a dwelling if the I/R was 2.0Mohm?

The regs values are the as a min safety values....

well iwouldn`t walk away as it stands now as the min. acceptable IR is 1 MEG...not 2.....

 

[JONOXNAM]

well iwouldn`t walk away as it stands now as the min. acceptable IR is 1 MEG...not 2.....

Ah yes as of 1st Jan.... but I was more trying to point out even at 2Meg so that would be 2x the min would you really be happy to walk away.... but the regs say you have a clear conscience?

 

[Deleted member 9648]

I would just ask one Q for all the people who believe the regs values are the end of... if we switch to I/R - would you walk away from a dwelling if the I/R was 2.0Mohm?

The regs values are the as a min safety values....

As above...1 meg...
On a new install I would not accept one...or two megs because from experience I would expect a new install be to be a lot higher.
On an existing install.(PIR?)...yes...because I know from experience that there are many,many perfectly sound existing installs with IR's circa 1-2 megs
which require no attention at all,and I wouldnt waste a clients money attempting to improve it.
I would also point out that under the 15th edition...(not that long ago)...the minimum was 0.5 megs.

 

[GLENNSPARK]

Ah yes as of 1st Jan.... but I was more trying to point out even at 2Meg so that would be 2x the min would you really be happy to walk away.... but the regs say you have a clear conscience?

as of the 1st of Jan?..what 2012?...i think not mate.....was 1 meg when the 17th edition kicked off...if testing at the tails (all at once) then 2 MEG...if less than this value then you would test individually...but as has been said here n all...if i was getting near these kind of values then it would be prudent to recommend to the client that some remedial works may be due......

 

[Engineer54]

I wish you'd been invited to the Guidance Note 3 Amendment panel that I attended, if you'd produced all the evidence and research to back up your argument (none) then we could have revised this lethal 200 Ohm figure and saved countless lives in the process.

Until then I'll just continue with my reckless adherence to all published guidance on the subject.

You're beginning to make me laugh now, so what evidence (published or otherwise) have you got to hand that say's i'm wrong and your 100% right?? None, zilch, Zero, Your basically totally relying on an RCD for your total protection/disconnection. Forget your flowery semantics, and trying to look clever here, as i can remember you and others on here talking about trying to convince some panel you/they were invited too, to lower this numbty 200ohm threshold. So at one time or another, you too thought it an unrealistic value also, but now it's not , ...Right!! ...lol!!!

Another thing, this figure of 200 ohms is talking about stability, now how the hell an Ra value, can be related to stability is something i'd love someone to explain to me?? Can you IQ, ....seeing as your so clever and knowledgeable and experienced on this subject?? I must have missed something along the way, during the 1000's of rods i've been responsible for putting in the ground!!

As i've said to you and others here.... you do whatever you want to do, so by all means, you follow these published guidance's, but please don't tell me that's it's me that's talking nonsense here, ...because i most certainly am not!!

 

[Deleted member 9648]

You're beginning to make me laugh now, so what evidence (published or otherwise) have you got to hand that say's i'm wrong and your 100% right?? None, zilch, Zero,Kindly provide the evidence (published or otherwise) to say you are right and Bs 7671 is wrong then Your basically totally relying on an RCD for your total protection/disconnectionSee 411.5.2. Forget your flowery semantics, and trying to look clever here, as i can remember you and others on here talking about trying to convince some panel you/they were invited too, to lower this numbty 200ohm threshold. So at one time or another, you too thought it an unrealistic value also, but now it's not , ...Right!! ...lol!!!

Another thing, this figure of 200 ohms is talking about stability, now how the hell an Ra value, can be related to stability is something i'd love someone to explain to me?? Can you IQ, ....seeing as your so clever and knowledgeable and experienced on this subject?? I must have missed something along the way, during the 1000's of rods i've been responsible for putting in the ground!! Given that a 30ma RCD will provide EFP up to an Ra of 1667ohms minus final circuits R1+R2 that leaves a comfort zone of 1447 ohms for increase in ground resistance....I'd call that reasonably stable.

As i've said to you and others here.... you do whatever you want to do, so by all means, you follow these published guidance's, but please don't tell me that's it's me that's talking nonsense here, ...because i most certainly am not!!

..........

 

[IQ Electrical]

You're beginning to make me laugh now, so what evidence (published or otherwise) have you got to hand that say's i'm wrong and your 100% right?? None, zilch, Zero, Your basically totally relying on an RCD for your total protection/disconnection. Forget your flowery semantics, and trying to look clever here, as i can remember you and others on here talking about trying to convince some panel you/they were invited too, to lower this numbty 200ohm threshold. So at one time or another, you too thought it an unrealistic value also, but now it's not , ...Right!! ...lol!!!

Another thing, this figure of 200 ohms is talking about stability, now how the hell an Ra value, can be related to stability is something i'd love someone to explain to me?? Can you IQ, ....seeing as your so clever and knowledgeable and experienced on this subject?? I must have missed something along the way, during the 1000's of rods i've been responsible for putting in the ground!!

As i've said to you and others here.... you do whatever you want to do, so by all means, you follow these published guidance's, but please don't tell me that's it's me that's talking nonsense here, ...because i most certainly am not!!

I've never 'attempted to lower the 200 Ohm value.'

This isn't about you or me being right or wrong or looking clever, it's about you castigating myself and other members for handing out advice on TT installations fully in line with published guidelines and British Standards and propogating the myth that this advice is somehow dangerous.

For the last time, please give me any evidence of just 1 case where there has been an injury or death as a result of following the published guidelines on TT installations....

Last time.......

 

[Engineer54]

..........

Ha ha .... you mean you actually need evidence that a 200ohm Ra is a nonsense?? I Really can't even be bothered to answer that, or your relationship of an RCD mA rating to the stability of an earth electrode... your just pulling at straws now!! lol!!

If you missed the drift here wirepuller, RCDs have a tendency to Fail quite often, they are all well and good when functioning correctly, ....were talking about when FAIL!!

 

[GLENNSPARK]

well i will throw my too penneth in n all and say that RCDs not liking damp conditions (cellars) where a lot of C/Us can be found......

 

[Engineer54]

I've never 'attempted to lower the 200 Ohm value.'

This isn't about you or me being right or wrong or looking clever, it's about you castigating myself and other members for handing out advice on TT installations fully in line with published guidelines and British Standards and propogating the myth that this advice is somehow dangerous.

For the last time, please give me any evidence of just 1 case where there has been an injury or death as a result of following the published guidelines on TT installations....

Last time.......

I'm castigating no-one... but when someone tries to belittle me because he thinks he has to protect the UK way of doing things, then i will react!!

By the way, why is it always me that needs to prove this or that, to You, ...but you can't or won't move on anything i ask?? i asked you a question in my last post, that has like any other question/query been totally skipped over in favour of another line of ridicule ...

What myth, there's no myth there at all, the probability is plainly there, ...as for evidence, i can't, exactly the same as you can't show any evidence that it hasn't done so!! But i have already stated that in an earlier post didn't i ??

 

[IQ Electrical]

Belittle? I can't be doing with paranoia.

I'm sitting in my office surrounded by publications 'backing up' my beliefs and opinion, do I just send them over?

They are UK publications but that's where I carry out my lethal TT installations.

 

[La Poste]

What I will say is, in generally found garden British soils, I could in most circumstances achieve a below 10ohm Ra with a maximum of 2 twin rod positions.

I'm not taking sides in this debate or anything like that but I would really love some advice on how to achieve this or anywhere near this value with two twin rods.

Thanks

 

[Engineer54]

Belittle? I can't be doing with paranoia.

I'm sitting in my office surrounded by publications 'backing up' my beliefs and opinion, do I just send them over?

They are UK publications but that's where I carry out my lethal TT installations.

Did i say you ..?? And i don't do paranoia

Surrounded, wow!! Send them over, by all means, ...I'll be happy to peruse your publications backing up your beliefs!!

I see your still ''trying'' to be clever!!..... lol!!

 

[Deleted member 9648]

I'm castigating no-one... but when someone tries to belittle me because he thinks he has to protect the UK way of doing things, then i will react!!

It's got nothing to do with 'protecting the UK way of doing things' E54....I recall you 'accusing' me of patriotism during a previous TT/Ra skirmish a while ago. But you miss the point....This is a BRITISH STANDARD ffs....it's not like this is being made up. I spent 5 years as an apprentice being taught that 'the regs' as they were then,are the bible....nothing has changed....If the powers that be deem that a change is required to british standards on TT systems I will change my practices accordingly,untill such a change,complying with Bs 7671 cannot be unsatisfactory,dangerous...or any other accusation you may care to throw at it....and is the correct advise to give to TT questions on a UK based forum.

 

[IQ Electrical]

Did i say you ..?? And i don't do paranoia

Surrounded, wow!! Send them over, by all means, ...I'll be happy to peruse your publications backing up your beliefs!!

I see your still ''trying'' to be clever!!..... lol!!

You posted the comment under my quoted post.

You're slaughtering me with facts and hard evidence, along with the 'trying to be clever' comments, if you pay the courier costs, I'll send my publications over, I'll meet the costs for yours lol!

Of course they're all based on pathetic British Standards that have been proven adequate over many decades but don't let that sway the argument!

 

[Engineer54]

You posted the comment under my quoted post.

You're slaughtering me with facts and hard evidence, along with the 'trying to be clever' comments, if you pay the courier costs, I'll send my publications over, I'll meet the costs for yours lol!

Of course they're all based on pathetic British Standards that have been proven adequate over many decades but don't let that sway the argument!

I have indeed posted comments under your posts, ...???

You hide behind your publications, but if you honestly believe what your defending, then i really don't know what to think!! You stick to your RCDs that haven't harmed anyone, .....well, not that You've read about anyway!! Geezus!!

Still nothing on anything i've asked you then i see?? Can't you quote anything from any of these publications that are surrounding you, on my last Query of you??

You mean like your slaughtering me with all of yours, ...lol!! As i stated before, you stick with your pathetic standards, that relates 200ohms Ra with stability, ...while i'll continue to install TT systems of all types and descriptions safely and correctly....lol!! But i don't think you'll find a mention of 200 ohms going back past the 15th edition!!

If i were to produce a TT system of anywhere approaching your magical 200 ohms, on any of my projects large or small, which i might add are fairly strongly based on BS7671, ...i'd be hung drawn and quartered , ...and quite rightly so too!! But hey, it's a good-un, ... it says so in BS7671.

I guess you'd be arguing the point all the way to the airport, with all your magnitude of publications.... And that is just about as pathetic as your argument goes!!!

 

[Engineer54]

It's got nothing to do with 'protecting the UK way of doing things' E54....I recall you 'accusing' me of patriotism during a previous TT/Ra skirmish a while ago. But you miss the point....This is a BRITISH STANDARD ffs....it's not like this is being made up. I spent 5 years as an apprentice being taught that 'the regs' as they were then,are the bible....nothing has changed....If the powers that be deem that a change is required to british standards on TT systems I will change my practices accordingly,untill such a change,complying with Bs 7671 cannot be unsatisfactory,dangerous...or any other accusation you may care to throw at it....and is the correct advise to give to TT questions on a UK based forum.

I don't believe that you can't think for yourself, and need to rely on every quotation in the Reg's to perform your trade as an electrician Wirepuller, your better than that. As been proved in the many good posts you've made on the Forum. ...On that note, i'll say no-more!!

 

[Dave 85]

To the OP:
You dont seem to have any idea how testing actually works. Its no use randomly pulling figures from the regs book if you don't actually understand them. Your Zs reading should be approx Ze plus R1=R2 (It is, after all, exactly the same test, just furthur from the source) so if your max Ze on a TT is 200ohm (which is what my assessor always tells me to aim for) Then as long as your Zs is, for arguments sake, less then 200ohm aswell, you're fine. The fact that your Zs is so much lower suggests you must be getter a far better earth from the water main than you are getting from the earth stake.