Confirming earth bonding continuity when cannot isolate supply

[Amusingold]

Hi, just wondering how other sparks, go about confirming main earth bonding continuity when supply cannot be isolated, ze and pfc can be enquired wich is fine but what happens if you cant disconnect main bonding earth, is previous test results good enough to confirm?visual checks good enough? can this be a limitation on a condition report or not? And how would we overcome this if it was an initial verification or a minor works, just wondering what's the minimum acceptable to tick those boxes.

Theres so many variables it's hard to gauge what would be acceptable to tick those boxes on test certs.

Help much appreciated

Many thanks

 

[Deleted account]

Simple answer is you can’t.

why can’t you isolate the supply?

is it a hospital, manufacturing factory....?

 

[i=p/u]

its continious, you can see both ends, tick that box, if you reallly worried just tick/write not verified

 

[Ian1981]

You can’t simply say that the main bonding cannot be verified for initial verification for new work or additions as per regulation 132.16.

 

[i=p/u]

Well it shouldnt be in service then mucker, just my 2c

 

[pc1966]

You can normally confirm the Zs and PFC by measurement without isolating the supply.

Of course that assumes you can access the terminals safely without isolation, and that is something you should consider very carefully before attempting it. Many panels and switch-fuses have mechanical interlocks to avoid being opened in the energised position for very obvious safety reasons, and even removing covers that might expose live busbars is something you really ought not to do live in case of accidental contact.

What you cannot do without isolation is confirm Ze as that requiers the supply earth to be isolated from the installation to measure without any parallel earth paths via bonding to service pipes, structural parts, lightning conductors, etc.

 

[i=p/u]

is previous test results good enough to confirm?visual checks good enough? can this be a limitation on a condition report or not?

Who said that?

 

[Ian1981]

Not sure I understand what you mean?
I’m simply saying that for initial verification you cannot state that the bonding conductors haven’t been verified as adequate for the new or altered works.
The regulation is in fundamental principles of bs7671

 

[pc1966]

A bit more background on why it can't be isolated, and the size/complexity would help.

If you have access to the incoming supply point somewhere and the earth is routed in some non-obvious way, you could always use a wander lead and confirm it is at the expected sort on resistance (guess X metres route length, guess CSA at 16mm or whatever, look up table and compute)

 

[Amusingold]

Hi guys help appreciated, so the installation is an events venue, two massive transformers on site that feed two big switchboards, we dont have authority to start opening up the switchboards even if we could isolate, , is it acceptable to start disconnecting main incoming earths from buss bars etc, it just seems very intrusive work on a big install for conditon report, and the same stands for initial verification, I wouldn't have thought every time we add a 20amp radial circuit off a sub main board, we have to isolate the whole venue and strip down a switchboard. This is why I would have to inquire ze and pfc wich helps me there but then it's the ticking of main earth and main bond "connection/continuity varified" the way I see it it is asking connection or continuity verified so would previous results and a visual be enough to tick without a lim as like you say we cannot lim on initial verification How would you guys go about those situations, condition report and initial verification.

I feel this is a common situation and people would just have a quick look and give it a tick but I like to be as furough as possible and wonder if I'm missing a trick.

 

[Lister1987]

Hi guys help appreciated, so the installation is an events venue, two massive transformers on site that feed two big switchboards, we dont have authority to start opening up the switchboards even if we could isolate, , is it acceptable to start disconnecting main incoming earths from buss bars etc, it just seems very intrusive work on a big install for conditon report, and the same stands for initial verification, I wouldn't have thought every time we add a 20amp radial circuit off a sub main board, we have to isolate the whole venue and strip down a switchboard. This is why I would have to inquire ze and pfc wich helps me there but then it's the ticking of main earth and main bond "connection/continuity varified" the way I see it it is asking connection or continuity verified so would previous results and a visual be enough to tick without a lim as like you say we cannot lim on initial verification How would you guys go about those situations, condition report and initial verification.

I feel this is a common situation and people would just have a quick look and give it a tick but I like to be as furough as possible and wonder if I'm missing a trick.

Course you wouldn't, that's what Zs@DB is for.

 

[Amusingold]

Course you wouldn't, that's what Zs@DB is for.

Zs at db on the test shchedual yes but that doesnt satisfy the ze and PFC at origin section on the top sheet for an initial verification does it? These are two different tests

 

[Amusingold]

Zs at db on the test shchedual yes but that doesnt satisfy the ze and PFC at origin section on the top sheet for an initial verification does it? These are two different tests

Or confirmation of main earth and main bonding earth as you haven't isolated.

 

[Lister1987]

Zs at db on the test shchedual yes but that doesnt satisfy the ze and PFC at origin section on the top sheet for an initial verification does it? These are two different tests

I believe it would. The purpose is to check that the fault path is unbroken no? (Values will of course be higher due to length)

Came across this; https://---------------/forums/forum/messageview.cfm?catid=205&threadid=26810

 

[Lister1987]

Also let's not forget the 3 accepted methods of obtaining Ze; Measurement, Calculation or Enquiry. All 3 are acceptable and would fill that gap for you.

 

[Amusingold]

I believe it would. The purpose is to check that the fault path is unbroken no? (Values will of course be higher due to length)

Came across this; Electrical Blog - Electrical Advice | Free Electricians Advice Forum - https://electriciansforums.co.uk/forums/forum/messageview.cfm?catid=205&threadid=26810

Yes but ze needs to be done at origin with earth disconnected, by just copying your zs at db result this includes parallel earth paths, and also would be from db not origin , so I would have thought we enquire everytime, and then visual check for earth and main bond connection. Cant think of any other way to do it without isolation and very intrusive work on a switchboard? Thanks for your reply, notsure what the link was supposed to show me... was just a webpage with no thread...

 

[Vortigern]

Not absolutely foolproof due to parallel earths etc. but an approximation closer than no test at all is from MET wander lead to pipe in proximity of clamp if a low reading >1 ohm then there is some evidence their is continuity. What do others think?

 

[westward10]

There is every chance there is no earthing conductor from the transformer anyway and that your main earth bars are bonded to the supply neutral.

 

[pc1966]

If it is a venue with its own transformers than the supply Ze is going to be quite low and if you know the approx length and type of the sub-main cable to your board you could be fairly confident that a Zs measured there is in close enough agreement to establish the supply arrangement is sound.

Also it probably has the installation & test results from before and if it appears to be sound and well maintained than you would have no reason to doubt it unless the Zs looked oddly high.

 

[Amusingold]

Yes all this is correct , so I would have thought visual would be fine for earth connection tick box, and ze and pfc just put down enquired values? Or would you feel comfortable writing a zs at sub main value in the ze section? As enquiry is acceptable for ze and pfc I think I would just put enquired values, but obviously safe in the knowledge we have good earths from visual and like you say previous install test results. You have confirmed in similar thinking to me and dont think theres any other way around it. Thanks for everyones input!

 

[ipf]

If you cannot access to test, use additional notes to explain.

For example:
SUPPLY CHARACTERISTICS AND EARTHING ARRANGEMENTS and PARTICULARS OF INSTALLATION AT THE ORIGIN.
These sections of the certificate have not been fully completed due to the lack of access and lack of information where required.

 

[Amusingold]

If you cannot access to test, use additional notes to explain.

For example:
SUPPLY CHARACTERISTICS AND EARTHING ARRANGEMENTS and PARTICULARS OF INSTALLATION AT THE ORIGIN.
These sections of the certificate have not been fully completed due to the lack of access and lack of information where required.

Good point thanks, but this wouldnt be acceptable on an initial verification, but yes could add a bit of detail on how supply characteristics ze pfc etc are enquired due to unable to isolate, I dont think zero value and a limitation would cut it wouldnt feel right claiming satisfactory without at least an enquired value for ze and pfc, and earthing tick boxes satisfied with visual, past test certs and annual service of transformers I feel is bags of proof of good earths.

Thank you everyone interesting and informative and backed up my thoughts and testing processes going forward. Good to hear everyones take on these certain scenarios they dont go into detail or cover at all in the classroom!

Peace !

 

[ipf]

Good point thanks, but this wouldnt be acceptable on an initial verification, but yes could add a bit of detail on how supply characteristics ze pfc etc are enquired due to unable to isolate, I dont think zero value and a limitation would cut it wouldnt feel right claiming satisfactory without at least an enquired value for ze and pfc, and earthing tick boxes satisfied with visual, past test certs and annual service of transformers I feel is bags of proof of good earths.

Thank you everyone interesting and informative and backed up my thoughts and testing processes going forward. Good to hear everyones take on these certain scenarios they dont go into detail or cover at all in the classroom!

Peace !

I'm talking along the lines of industrial or large commercial, really. You can only test what you CAN test, though, no matter what the installation.
I must admit, I have never done the example in a domestic situation. There's generally a way round it. If you cant get a Ze, at least you can get Zs at db and explain that in notes.

 

[loz2754]

The initial verification you are doing is only for the additional circuit you have installed, not the whole installation. Therefore, in my opinion, as long as the Zs at the DB it's installed from is ok and the R1+R2 etc are ok then you have done what is reasonably practicable to ensure ADS is met. With a note on the certificate to explain this.

 

[loz2754]

@ipf Why the dislike if you don't mind me asking?

 

[Amusingold]

The initial verification you are doing is only for the additional circuit you have installed, not the whole installation. Therefore, in my opinion, as long as the Zs at the DB it's installed from is ok and the R1+R2 etc are ok then you have done what is reasonably practicable to ensure ADS is met. With a note on the certificate to explain this.

Yes I accept that as good enough to tick the earthing boxes, but as for ze and pfc at origin if I couldnt isolate I would enquire, as putting as zs
at db value in as ze would be wrong in my eyes.

Again thanks for everyones input! Much appreciated guys

 

[loz2754]

Yes I accept that as good enough to tick the earthing boxes, but as for ze and pfc at origin if I couldnt isolate I would enquire, as putting as zs
at db value in as ze would be wrong in my eyes.

Again thanks for everyones input! Much appreciated guys

I'm not suggesting putting a Zs at DB in as Ze. That would indeed be incorrect. All I'm saying is that if your new circuit is fed from a sub DB, and it is impracticable to disconnect the earthing conductor at the origin, then you use the enquiry method for the Ze, measure Zs at the sub DB, also at the end of your new circuit. That is all you can do.

 

[loz2754]

Yes all this is correct , so I would have thought visual would be fine for earth connection tick box, and ze and pfc just put down enquired values? Or would you feel comfortable writing a zs at sub main value in the ze section? As enquiry is acceptable for ze and pfc I think I would just put enquired values, but obviously safe in the knowledge we have good earths from visual and like you say previous install test results. You have confirmed in similar thinking to me and dont think theres any other way around it. Thanks for everyones input!

PFC is measured with the earth conductor connected.

 

[Amusingold]

I'm not suggesting putting a Zs at DB in as Ze. That would indeed be incorrect. All I'm saying is that if your new circuit is fed from a sub DB, and it is impracticable to disconnect the earthing conductor at the origin, then you use the enquiry method for the Ze, measure Zs at the sub DB, also at the end of your new circuit. That is all you can do.

Ahh yes to satisfy the main earth conductor tick box, yes, totally agree, apologies, good to hear everyones opinion, like I said earlier they don't traxh these real world scenarios at in the class room! And even when the questions are raised the tutors seem to shrug them off as they have no real on the job experience!

Thanks again

 

[i=p/u]

Ahh yes to satisfy the main earth conductor tick box, yes, totally agree, apologies, good to hear everyones opinion, like I said earlier they don't traxh these real world scenarios at in the class room! And even when the questions are raised the tutors seem to shrug them off as they have no real on the job experience!

Thanks again

not like classroom. Ul find some meters willl give you same reading for zdb and ze, deoending on distance apart. Or even less. i.e
Ze =0.32.
Zdb 0.31

 

[pc1966]

Sadly none of the MFT do 4-wire Kelvin style measurements for Zs/PFC, so uncertainty of several 0.01R is just part of the game depending on just where and how hard the probes are in contact.

Only the very expensive high current loop testers do that it seems. It is a shame no MFT even offer it as an extra cost feature as I would have been happy to shell out and extra £50-100 for some Kelvin style crocodile leads (where each jaw has a separate cable, and one per clip is the test current and the other is observing the dolt drop, eleiminating the test cable's effect).

 

[ipf]

@ipf Why the dislike if you don't mind me asking?

Sorry mate. Complete accident and just seen........wiped. I see we can, that's good.?

As well....some of my comments in this thread are a bit over the top.......I didn't notice that the OP was talking MWC. My fault.?

 

[loz2754]

Sorry mate. Complete accident and just seen........wiped. I see we can, that's good.?

As well....some of my comments in this thread are a bit over the top.......I didn't notice that the OP was talking MWC. My fault.?

Cheers bud?