basic bad practice

S

Stevesplatto

-
Found this on a large testing companies website:

'Where the mains supply is connected, as will be the case for periodic testing, the protective and equipotential conductors must not be disconnected because if a fault occurs these conductors may rise to a high potential above earth. In this case, an earth-fault loop tester can be used to verify the integrity of the protective system.'

So wrong, I wonder how many wrongly measured Ze readings they've reported (parallel paths). I emailed them suggesting they might consider turning of the main isolator to reduce the risk of the conductors rising to 'a high potential above earth' before disconnecting the main earth for a real Ze test..
Big company as well..

Ride em cowboy!
 
I disagree with what you say. I believe that they are referring to sites which run 24/7 and cannot be switched off entirely. They are not proposing to measure Ze, but Zs. Measuring Zs will , assuming acceptable results, confirm adequate earthing for protective devices to operate. They mention the protective system, which is the combination of the distributor's earthing system and the bonding (in parallel).
 
Stevesplatto said:
Found this on a large testing companies website:

'Where the mains supply is connected, as will be the case for periodic testing, the protective and equipotential conductors must not be disconnected because if a fault occurs these conductors may rise to a high potential above earth. In this case, an earth-fault loop tester can be used to verify the integrity of the protective system.'

So wrong, I wonder how many wrongly measured Ze readings they've reported (parallel paths). I emailed them suggesting they might consider turning of the main isolator to reduce the risk of the conductors rising to 'a high potential above earth' before disconnecting the main earth for a real Ze test..
Big company as well..

Ride em cowboy!
Click to expand...


doesnt say anything about measuring Ze there, what they are saying is that instead of measuring Ze on an energised circuit it is ok to use a EFLI tester to measure Zs, this would determine that earthing arrangements of that circuit are adequate, have they emailed you back yet????
 
As said turning off a large installation that runs 24/7 is not going to happen. 95% of EICR I do are like this. Massive warehouses that dont stop or data centres that CANNOT be turned off.

You couldnt walk into a food production factory like walkers where downtime cost thousands and ask them could I switch the main switch off so I can gain an accurate Ze, its not going to happen.
 
No this isnt talking about a food factory that can't be shut down...

This is a general description of testing procedures. Normal practice is to obviously isolate the supply for continuity tests.

I'm not sure how a Zs test alone can fully verify the integrity of the protective conductors without an R1/R2 (dead test) as suggested. Suppose the Ze could be determined by enquiry but it's not ideal...

Interesting how instead of seeing this as a general procedure and thus flawed some people saw this instead as a description of how to proceed when isolation isnt possible, which it wasnt, and rose to it's defence. Looked for ways it could be right. Guess I should have pasted the entire article!

Cheers
s

PS I did gt a eply asking for the page URL
 
doing a ze test were you cant switch of the supply is known as zdb which as im led to belive is acceptable were it is not practable to isolate supply due to bussiness requirments
 
Farmelectrics is right on! Stop worrying about other peoples bad practice and worry about getting your own correct! The point of the inspection is to affirm the safety and integrity of the installation. If you haven't got the understanding of the agreed limitations then your in trouble. Zdb if fine! No bad practice there!
 
Yeah right! The regs do say 'by enquiry'. Ever tried to get a Ze spec in writing out of a supplier? And what if you suspect a problem with say a suppliers TN-S strap clamp (which I did just recently) they will ask you what the Ze is before they'll come out!
 
If you see a problem, thats a different scenario all together, doing Zs is fine otherwise surely?
 
To be frank I don't very often come across situations where I can't isolate the supply and carry out a Ze loop test and check continuity of the protective conductors. The situation I illustrated, a malfunction clamp, is a real situation which would not have shown up with a zs loop test with all protective conductors connected because of parallel paths... Where's my bad practice?
cheers
s
 
You don't have one bud! Just these threads alway nit pick to some degree. It's quite funny really! Every install needs to be assessed on its own merit. I do think your concern about Parallel earth path is less worry tho. If you loose the ze i would expect zdb to be just to high (ohm or two) and that's what your testing for eh? Enjoy.
 
Stevesplatto said:
How would you be able to ascertain the value of the supply earth (Ze) if you can't isolate it from protective bonding?
Click to expand...

well, you can't. However as mentioned you can do a Zdb. You can also carry out a visual and physical inspection of the earthing arrangements to ensure they are robust. I'm not convinced that your parallel paths concern is anything to worry over too much. Most gas and water mains are plastic now and so parallel paths are limited. Again, you can inspect for this.

It is called "inspection and test"

Stevesplatto said:
To be frank I don't very often come across situations where I can't isolate the supply and carry out a Ze loop test and check continuity of the protective conductors. The situation I illustrated, a malfunction clamp, is a real situation which would not have shown up with a zs loop test with all protective conductors connected because of parallel paths... Where's my bad practice?
cheers
s
Click to expand...

I don't believe anyone has accused you of any bad practice. I think you have misunderstood the replies.
Perhaps you should "bone up" on your i&t.
 
I work in West London mostly and the majority of the services I come across are still copper or lead.
I think I'm very well briefed on procedures, I even look up things occasionally ;-)
To re-cap. the discussion got round to; if you can't isolate the supply then obviously the protective conductors should not be disconnected. To substitute for a Ze a Zs (or 'Zdb' which strangely isnt in the regs P39 where you'd expect or on google..) is recommended. However, with all protective conductors connected there is the issue of parallel paths (unless you have all plastic gas and water) and the fact you don't have an R1/R2 because that's a dead test so calculating Ze is a little hit and miss.
Then there's the enquiry angle which in the real world (or at least in London) is almost impossible to get from a supplier and most of the time will only quote the minimum from the regs anyway..
Bad practice on my behalf was suggested by Mr WW and apparently I need to bone up on Inspection and testing procedures!

All that being said obviously a loop test is going to be the way you check continuity on a live installation. My point was, way back at the beginning is that it's not the default choice as a general procedure for an EICR as illustrated by the site quote that started this. You'd isolate the supply and loop test the Ze at least so the Zs's can be put into context. Or, do people just loop test the Zs's and that's it...

Anyway, interesting to see how this forum works when you stick your head over the parapet with an opinion!

Cheers
s

I'm well aware of the 'agreed limitations' caveat (and also the way it's abused!).
 
farmelectrics said:
any one ever done ze with earth connected and then retested when disconected never much in the readings and sometimes the same reading anyone had same issues
Click to expand...

I might try that later...do a true Ze then test with all earths connected then just through the water and gas pipes.
 
There is no actual guide to Zdb testing, but when I did my 2400 many many moons ago this was how I was trained to do it and how it is done

With the equipotential bonding conductors connected we can make a Zdb test at the distribution board, the test is carried out and the value recorded. If there is any difference between the recorded value of Ze and the recorded value Zdb then this difference is the value of the parallel paths associated with the equipotential conductors and this value must then be added to all subsequent measured values of Zs.
 
Stevesplatto said:
To be frank I don't very often come across situations where I can't isolate the supply and carry out a Ze loop test and check continuity of the protective conductors. The situation I illustrated, a malfunction clamp, is a real situation which would not have shown up with a zs loop test with all protective conductors connected because of parallel paths... Where's my bad practice?
cheers
s
Click to expand...
HOW do you Issolate the supply fully? If its by removing DNO fuse then you are acting Illegaly and by recording this on cert you are admitting your guilt
 
mogga said:
HOW do you Issolate the supply fully? If its by removing DNO fuse then you are acting Illegaly and by recording this on cert you are admitting your guilt
Click to expand...
i thgink he meant isolating the installation by the main switch in the CU , so as to be able to disconnect main earth to measure Ze.
 
Stevesplatto said:
Found this on a large testing companies website:

'Where the mains supply is connected, as will be the case for periodic testing, Perhaps 'will' should be replaced with 'may'.....the protective and equipotential conductors must not be disconnected because if a fault occurs these conductors may rise to a high potential above earth. In this case, an earth-fault loop tester can be used to verify the integrity of the protective system.'

So wrong, I wonder how many wrongly measured Ze readings they've reported (parallel paths). I emailed them suggesting they might consider turning of the main isolator to reduce the risk of the conductors rising to 'a high potential above earth' before disconnecting the main earth for a real Ze test..
Big company as well..

Ride em cowboy!..rather harsh....I dont really think where an install cannot reasonably be isolated for testing a Ze inludiing parallel paths is a cowboy practice...more of an operational necessity on occasion.
Click to expand...
.................
 
wirepuller said:
.................
Click to expand...
I didnt paste the whole page but this was part of a description for general practice in periodic inspection and testing. My point way back then was good practice would be to isolate the installation in the first instance. The cowboy thing was more in jest really, I'm sure they're a good company. Discussion moved on a bit to how satisfactory using a loop test for Zs would be. Although Ze can be arrived at by enquiry supposing there was say a problem with the DNO's strap on a TN-S which a Zs may not p/u because of parallel paths/ and so on..
Good to question these things from time to time I think...
Cheers
s
 
It seems his point has been lost, with the replies giving the alternative and regular situations where procedure has to be adapted

The way I read the post,the company are making their own real world experiences a set procedure in deference to the IEE, rather than a substitute for procedures which often have to be adapted because of necessity
 
Stevesplatto said:
Yeah right! The regs do say 'by enquiry'. Ever tried to get a Ze spec in writing out of a supplier? And what if you suspect a problem with say a suppliers TN-S strap clamp (which I did just recently) they will ask you what the Ze is before they'll come out!
Click to expand...

I think having just achieved the C&G2391 is just the beginning of the journey.
Ze, by inquiry is already available to you since the DNO will quote their maximum standard value. In fact they probably won't even bother to reply to you, because you should know this. However, the Ze will rarely be the maximum quoted value. and would be better measured.
Now smaller installations where complete isolation is possible then a Ze can be performed by disconnecting the earthing conductor from the MET. But anything larger, where total isolation is inconvenient or impossible then you must not disconnect any of the main protective conductors.
A Zs close to, or at, the main intake is perfectly acceptable method of verifying that there is a protective system in place and to verify that the TNS sheath is still providing a reasonable result
 
ackbarthestar said:
I think having just achieved the C&G2391 is just the beginning of the journey.
Ze, by inquiry is already available to you since the DNO will quote their maximum standard value. In fact they probably won't even bother to reply to you, because you should know this. However, the Ze will rarely be the maximum quoted value. and would be better measured.
Now smaller installations where complete isolation is possible then a Ze can be performed by disconnecting the earthing conductor from the MET. But anything larger, where total isolation is inconvenient or impossible then you must not disconnect any of the main protective conductors.
A Zs close to, or at, the main intake is perfectly acceptable method of verifying that there is a protective system in place and to verify that the TNS sheath is still providing a reasonable result
Click to expand...
(When did 2391 come into this?)
I think I said that didnt I? DNOs don't give real world values and just quote regs. My point was that the procedure of NOT isolating the supply, disconnecting the main earth and measuring Ze was cited as the default method. The example you give of taking a Zdb while accepted practice when the supply cannot be isolated (not 'convenient' is not a reason) isnt ideal because of bonding to gas/water etc which in many cases gives a better reading than the Distributors! So it won't give a true measure of the condition of the distributors earth. it's a compromise...

Cheers
s
 
(not 'convenient' is not a reason)
Click to expand...
As far as business is concerned it is a very good reason why the supply cannot be disconnected.

However, when conducting a PIR/EICR, verification of the protective system to the distribution boards and final circuits is achieved by the measurement of the earthing system connected since this is what its there for. You wouldn't expect to have a real fault under test conditions would you?
There are those 'purists', when doing a PIR, who believe the only way to test final circuits is to isolate each one in turn and live test separately. That method might be Ok for a small installation where you have total and continual control of the isolation process, but this is very rarely the case and so other suitable methods have to be used to assess the worthiness of the protective systems. Zs/Zdb is one method.
 
Well, I think for the majority of the 22million households in the UK it's entirely practical to follow GN3 and safe working practice and isolate the supply. As stated the Zs method won't pick up all potential faults and should not be used as a first choice method, clearly..
I find it really odd how the scenario that applies to the majority of domestic situations is ignored and the exception is somehow presented as the norm to defend a company that presents Zs testing as its default method. Sniddy little comments questioning my good practice and commenting on experience and qualifications that havnt been stated kinda soured what could have been decent discussion. I wonder how many on here just take a set of Zs readings and simply make up the continuity figures... (but that's a diferent thread..)
A lesson learned...
 
Found this on a large testing companies website:

'Where the mains supply is connected, as will be the case for periodic testing, the protective and equipotential conductors must not be disconnected because if a fault occurs these conductors may rise to a high potential above earth. In this case, an earth-fault loop tester can be used to verify the integrity of the protective system.'

So wrong, I wonder how many wrongly measured Ze readings they've reported (parallel paths). I emailed them suggesting they might consider turning of the main isolator to reduce the risk of the conductors rising to 'a high potential above earth' before disconnecting the main earth for a real Ze test..
Big company as well..

Ride em cowboy!
Click to expand...

and then....

Well, I think for the majority of the 22million households in the UK it's entirely practical to follow GN3 and safe working practice and isolate the supply. As stated the Zs method won't pick up all potential faults and should not be used as a first choice method, clearly..
I find it really odd how the scenario that applies to the majority of domestic situations is ignored and the exception is somehow presented as the norm to defend a company that presents Zs testing as its default method. Sniddy little comments questioning my good practice and commenting on experience and qualifications that havnt been stated kinda soured what could have been decent discussion. I wonder how many on here just take a set of Zs readings and simply make up the continuity figures... (but that's a diferent thread..)
A lesson learned...
Click to expand...

Lol....
 
Stevesplatto said:
Well, I think for the majority of the 22million households in the UK it's entirely practical to follow GN3 and safe working practice and isolate the supply. As stated the Zs method won't pick up all potential faults and should not be used as a first choice method, clearly..
I find it really odd how the scenario that applies to the majority of domestic situations is ignored and the exception is somehow presented as the norm to defend a company that presents Zs testing as its default method. Sniddy little comments questioning my good practice and commenting on experience and qualifications that havnt been stated kinda soured what could have been decent discussion. I wonder how many on here just take a set of Zs readings and simply make up the continuity figures... (but that's a diferent thread..)
A lesson learned...
Click to expand...

From what you have posted it doesnt say if its domestic, commercial or industrial...with the method they have described we just took the job as being in an industrial/commercial situation where the power cant be switched off for various reasons. I took it from being a large testing company that they will mostly be testing that sort of installation rather than being domestic where most people get a local spark IMO...

May be better if you posted up a link to the site...
 
Since 1986 I have worked for several very large companies, and every one of them has had an annual "shutdown", where engineering gets total control of the place for a week or two for the purpose of carrying out essential work which can't be done during production. I understand that certain institutions need to run 24/7, 365, but there are many occasions when isolation is quite possible but it is easier not to bother due to the hassle of resets etc.
I understand the economics completely, and I'm not saying that certain alternative methods (assuming you have the original system Ze readings as reference) are wrong, but it is funny how certain practices (such as storing fuel) go out of the window when it suits for political or financial reasons.
 
I agree, if you can get a full shut down then there are all manner of tests that can be done to verify compliance with the regs.
However, as far as I can see there are some companies that rely on preventative maintenance using fully automated management systems which would be impossible to test in 'conventional' terms.

Basic one isolator one distribution board domestic systems can be verified easily by switching off. But why would you need to if previous results were available, an inspection showed that all the main bonding conductors and other earthing arrangements were in place? You then only need to verify, Protective measures, IP ratings, Breaking capacities, Maximum demand and that disconnection will occur within the stated times and that a 'Numpty Ban' label was attached to the consumer unit
 

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