Advice on testing . . . please

[vickery1971]

Hello All,

I am after some advice as I have the opportunity to do some work (upgrading old consumer units) on a couple of empty flats for my next assessment. The trouble is I have never done a Board change in flats before (as I am only a novice), and as usual they are sub boards running from split three phase supplies via old metal box isolator switches with 60A fuses. The cable from the isolators to the boards is 10mm T&E and from the look of it someone ran a 10mm earth to each board too.

My questions are, how do I go about testing ze (it’s a tncs system) as all the earths from all the flats go to a Henley block in 10mm then one 16mm back to the service head, obviously I wont be able to cut everyone’s power to take all the earths out to avoid parallel paths, so any help here would be greatly received?

Next thing is my MEC to the board will only be 10mm, is that a strict no-no or do I just write that on the cert?

Thanks in advance for any advice you can give.

 

[vickery1971]

Or a rough pointer of where to look in the regs . . . . My brain hurts!

 

[i=p/u]

you could just do ze at main and r1 and r2 to each flat and add together, this is above me in expierience but but but but i could be right...

 

[vickery1971]

Thanks mate, its the best advice ive had yet! . . .

 

[i=p/u]

and only... hang round for bit, you might get better advice i was a novice and only progressing... so tread carefully in what i say...

 

[malcolmsanford]

Your EIC should just be concerned with the job your doing and so filling in the form should reflect that. Your changing a CU in a flat and that is it, the mains coming into the flat is not your remit and so you do not have to do anything concerning it. Providing there is no obvious signs of damage to the sub main, and your not adding to the loading, which you won't be then just change the CU and do the tests on the flat installation.

As far as the ZE is concerned you do not have to measure it, you can obtain that either by enquiry or calculation. Calculation will not be possible and I doubt enquiry will so I would do a Zs/Zdb, leaving the earths intact and note on your SoTR what you have done, and write on both the EIC/SoTR for Ze the Zs/Zdb and result.

 

[i=p/u]

calculation wouldnt work my way??? hmmmm i was feeling electricaly powerful their too

 

[GLENNSPARK]

Your EIC should just be concerned with the job your doing and so filling in the form should reflect that. Your changing a CU in a flat and that is it, the mains coming into the flat is not your remit and so you do not have to do anything concerning it. Providing there is no obvious signs of damage to the sub main, and your not adding to the loading, which you won't be then just change the CU and do the tests on the flat installation.

As far as the ZE is concerned you do not have to measure it, you can obtain that either by enquiry or calculation. Calculation will not be possible and I doubt enquiry will so I would do a Zs/Zdb, leaving the earths intact and note on your SoTR what you have done, and write on both the EIC/SoTR for Ze the Zs/Zdb and result.

yep...Zdb here malc.....

 

[vickery1971]

OK gents, thanks for the advice, just me worrying and over complicating things as usual. I will note that I have done Zdb instead of Zs on my EIC and SoTR and see how it goes. I am basically trying to do different things when im assessed each year as I figured if I don’t try different scenarios then I wont learn . . . . fingers crossed!

Just a quick question on the 10mm T&E with 10mm MEC . . . I take it I just state that on the cert? . . . or is it perfectly ok?

Thanks again for the advice!

 

[malcolmsanford]

Well you could put both down in the section concerning Main protective conductors ie 10mm + 4mm and add a comment in existing installation.

Is there any main bonding in the flats now?

 

[vickery1971]

Yes, there is 10mm from the Henley block running to the DB (16mm from Henley to service head) Gas is bonded where it enters the building for all the flats (from Henley to each meter box in 10mm, continuity confirmed visually) Water bonded in each flat, in 10mm from DB, and I could if need be bond the gas as it enters the flat.

The 10mm T&E feeding the board appeared to be only bonded at the DB in the flat, there is no earthing from the Henley block to the metal isolator box containing the 60A cut out fuse.

 

[Bul]

Malc
What does SoTR stand for. Sorry but I'm a bit behind with acronyms.

Great thread Vickery !

 

[trev]

Schedule of test results

 

[vickery1971]

Thanks, im not sure its such a great thread but I think it’s the setup I see in most of the flats I work in so worth a debate!