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Evening all,

My first post here, hope you are all welcoming :)

I have my QS assessment coming up next week with the NIC.

Question is, I am going to a property where I installed a 2way board, split the tails, upgraded the bondings etc. Straight forward job but the resident has a 24 hour oxygen supply running from DB1. Lovely old lady, I didn't want to turn the power off for her when I did the works, I tested my new board (db2) but with all the earths connected in as mentioned above I didn't want to turn the power off. 0.13 ohms, TNc-s.. all good.

I am just wondering if I am not able to turn the power off on DB1, therefore not disconnect any main earths, will the NIC let me test the ZE as an 'operational limitation' or as a zDb with it being a domestic property?

I understand 0.13 may not be a true representative of the earth fault path with the parallel earths connected, just wondering what I will say to the inspector when he asks me to perform a Ze test??

Long winded I know, but if you was in my shoes on the day what would be the correct way of going about this?

Many thanks all :)
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It would be unreasonable to make you perform the test or have the results on the test sheet. You may not cut power without the permission of the installation owner.
You've done the right thing and as said above, you may just get asked to talk through the test procedure.


Note on the cert that Ze was taken with parallel paths in place as no permission to isolate was granted by the owner.


Can’t see them asking you to do something to the detriment of the occupier. I’ve only been through the process once but get the impression they like to keep things quick and simple in order to tick the boxes and get on to the next appointment. 😜

Gavin John Hyde

I wouldn't worry too much, You can always do Zs at the board with explanation.

They dont have to get you to do every test, in my experience they do a selection from what is reasonable or practical on the day. they do always go through safe isolation though, so maybe demonstrate that on your home CU? or on DB2 at the site?
You can prove DB2 is isolated and check testing equipment against a known live supply DB1
On my visit I did the following tests.... i should add that on this install I couldnt verify where the water bodning was due to it being a property with carers and disabled resident. I had a 10mm at the board but couldn't find where it went too. my work was all in the garage. Assessor had no issue with that and accepted that real life is different to the books.

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