Confirming earth bonding continuity when cannot isolate supply

[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!