Confirming earth bonding continuity when cannot isolate supply

[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