Zdb = high Zs???

[jase]

benn putting in a new lighting circuit in a flat lately, all done and came to testing, tested the Ze at the board having isolated it and removed incoming earth so as to get no paralell paths, reading was 2.66 !!!
so went to the mains cupboard to look at getting the Ze of the whole building, but as there were 4 flats being fed of a busbar which is fed by a 3-phase tns and all the earths are in a MET, so isolating the incoming earth would have been a no-no without isolating the supply and was not wanting to just cut all the flats power, so could not get a true Ze, however, the way i look at it is that the Ze of the flat i am working in is 2.66 and that may be high due to paralell earth paths of the other flats, but that is what it is in practice and i cant change that, bit worried about filling in the cert tho as the Zs readings are above the maximum stated in the regs,, any thoughs??

 

[Spa Key]

benn putting in a new lighting circuit in a flat lately, all done and came to testing, tested the Ze at the board having isolated it and removed incoming earth so as to get no paralell paths, reading was 2.66 !!!
so went to the mains cupboard to look at getting the Ze of the whole building, but as there were 4 flats being fed of a busbar which is fed by a 3-phase tns and all the earths are in a MET, so isolating the incoming earth would have been a no-no without isolating the supply and was not wanting to just cut all the flats power, so could not get a true Ze, however, the way i look at it is that the Ze of the flat i am working in is 2.66 and that may be high due to paralell earth paths of the other flats, but that is what it is in practice and i cant change that, bit worried about filling in the cert tho as the Zs readings are above the maximum stated in the regs,, any thoughs??

Get your EFLI from the mains cupboard with everything still connected. You've already got parallel paths because everything is connected at the MET. That way you can tell whether it's a part of the building's installation at fault or the DNO have a problem their side.

Edit to add, the parallel paths of the other flats will bring the reading down, not up.

 

[GStueyXR]

the way i look at it is that the Ze of the flat i am working in is 2.66 and that may be high due to paralell earth paths of the other flats

Parallel paths lower your impedence mate.

This one simply must be sorted, dont certify without finding the fault mate.

 

[jase]

Went back there today and tested at the near the head at my flats isolater and on a small communal lighting board and this time the reading was 3.57!!!!! Got straight on the phone to EDF and they are sending someone out within the next 24hrs, hopefully they get into the building locate the head and rectify the issue, they have my mobile number should they need to call me, hopefully they will call me anyway so i can go and re-test all my zs.

Been an electrician for 8 yrs now but until recently only sub-contractor on site just containment and wiring to drawings it's not until you get really into things that you realise how much you need to know, this just threw me as wasnt sure it was something i was doing wrong, thanks for your help, i feel better knowing that not just the flat i am working in but also 3 others off of that head should now get sorted

i'll let you know how EDF get on.

 

[Sparky Ninja]

Just remember from what you have experienced here, that there are installations everywhere that have a system in need of upgrading or attention. I come across a couple a month at least.

The ze will always need to be obtained at the origin, and if you have suspicious zdb's or zs's and am unable to obtain the ze then contact the DNO and they will take it from there.


And yes, parallel paths reduce the reading as they supply a quicker return path

 

[vbyrne]

Get your EFLI from the mains cupboard with everything still connected. You've already got parallel paths because everything is connected at the MET. That way you can tell whether it's a part of the building's installation at fault or the DNO have a problem their side.

Edit to add, the parallel paths of the other flats will bring the reading down, not up.

whats EFLI in the mains cupboard??????

 

[Guest123]

whats EFLI in the mains cupboard??????

I believe he is refering to the Earth Fault Loop Impedance at the origin.....Ze.

 

[Spa Key]

I believe he is refering to the Earth Fault Loop Impedance at the origin.....Ze.

Yep sorry, should have been clearer.

 

[vbyrne]

Yep sorry, should have been clearer.

no probs, thought that |I was missing something

 

[jase]

3 days now and still nothing from EDF !!! phoned yesterday and they said someone had been to LOOK at the job but he wasnt back in the office till 4pm and they hadnt received his engineers report yet, i explained that there was a client waiting for a finished installation to be certified and building control are awaiting copies of those certs in order to sign off the work also pointed out that 3 other flats are fed from this supply,they said they would be in touch........................


do you think if this is not resovled by the end of the week it would be worth installing an earth rod myself???????

 

[Guest123]

The DNO have no resposibility to supply an earth facility......however, as they have supplied one in this instance, it is their responsibility to maintain it under the ESQCR. I would contact them again and insist that they do something about this situation straight away.

 

[jase]

They came out friday and did something, not quite sure what, except there is a big hole in the garden with a dirty great torpedo joint in it, and they have cut back some of the sheathing at the head, put a new earth on and changed the cutout, job done anyways, now reading .2ohm according to them and i got .39 at the CU so happy days