Advice on supply please!

bodders22 · Apr 30, 2011

Hi all,
I've just started a rewire on a 1920's ex local authority house. The supply is an underground cable with sheathed earth with a fairly new service head(BS1361), so I pressumed tns supply. On futher investigation the earth webbing goes into the neutral on the supply side and at the moment there is no earth to property from this(only off of lead water pipe).
Is this now classed as a tncs? and can I earth from neutral block on supply?
There were no seals so i've taken covers off to show you, Apologies for my ignorance but I've not come across this before,thanks in advance for any help!

telectrix · Apr 30, 2011

looks like it's been converted to TNC-S, but.... 1. where is the plastic shield from under the cut-out fuse? 2. that braid looks a bodge up. should be a terminal fitted linked to the neutral. i would call in the DNO as the set up looks a dodgy to me. have you measured Ze?

londonlec · Apr 30, 2011

You shouldn't have taken the cover off.

That silver braid is your earthing conductor, if it's damaged/short etc I beleive your DNO (UKPN in my area) will repair it FOC.

malcolmsanford · Apr 30, 2011

Unfortunately 542.2.4 tells us that if that is the lead pipe of a water utility then you can not use it as your earth electrode.

You are going to have to contact the DNO and advise them of what you have found. It does indeed look as though somewhere in the past someone, either the DNO or an electrician as converted this to a TNC-S via the water pipe.

Reg 542.2.4 is quite a new regulation though if my memory serves me right I think the use of gas and water mains used for an earth electrode was omited from the 16th.

What out of curiosty is the Ze for the system. I think this may have been done many years ago when this was acceptable to the DNO to do it, but under the current Regs and their own ESQCR-2002 it is not allowed. I'm sure if the DNO had done this, and with the braided earth. I put money on it being the DNO, then thye have an obligation to change it.

bodders22 · Apr 30, 2011

Thanks for fast replies.I've removed The shield just to take picture. The braid is bonded to the incoming electric supply unfortunatley not shown in picture). I haven't measured Ze as no main earth or can i measure it from braid? The cut out fuse does look quite new. thanks

oldtimer · Apr 30, 2011

bodders22 said:
Thanks for fast replies.I've removed The shield just to take picture. The braid is bonded to the incoming electric supply unfortunatley not shown in picture). I haven't measured Ze as no main earth or can i measure it from braid? The cut out fuse does look quite new. thanks

There is only one way of confirming what you have and that is temporary disconnect the braid and do a Ze test on it. But and I say BUT if you are not sure what you are doing the get the DNO to confirm supply type and to supply an earth point I have highlighted this on the forum before as I found 3 properties without earths or proper earths in the last 2 months plus their attitude was no earth so sad too bad but we can give you a quote if you want one. Typical Bl%$$$ government who allow these clowns to self regulate themselves leaving a masive grey area with regards to supplies when quite simply you cannot jump int a car without a current MOT because it need to be up to a specific standard yet we allow DNOs to add to their balance sheet with the O you dont have an earth well thats going to cost instead of Can you attend to this address as under the trades description act you electrical supply does not conform to the current standards

bodders22 · Apr 30, 2011

Thanks oldtimer, i'll do a Ze test as described on monday but perhaps i'll also call dno on tue's to see if they can confirm what I find.

marky sparky · May 1, 2011

dont tell them you took the covers off .

Geoffsd · May 1, 2011

bodders22 said:
The supply is an underground cable with sheathed earth ... so I pressumed tns supply... The braid is bonded to the incoming electric supply

Have I read this correctly?
Do you mean someone has connected the outer sheath of the incoming supply cable to the Neutral with this braiding?

bodders22 · May 2, 2011

hi Geoffsd, Yes you have read correctly, and as the house had almost no previous recent(approx 15 years) updates to the installation apart from a new service head I assumed it was the dno,also if an electrician had bothered to change to tncs would he/she not have connected it to something because as mentioned the only earth to any of the old cu's was from the lead water pipe.
I'm going to do a Ze test today and see what that tells me. If it reads as a tns should I'll change it back, if lower Ill contact dno.
Thanks

Geoffsd · May 2, 2011

It's a TNS-C-0

bodders22 · May 2, 2011

Have you come across this before? Is that what I put on cert? The Ze was 0.14.

Geoffsd · May 2, 2011

No. I was only making it up.

Is that 0.14 with the braiding disconnected from the neutral?

bodders22 · May 2, 2011

Yes that was with braid disconnected, looks like a call to dno tomorrow.

Geoffsd · May 2, 2011

Looks like TNS.

As you say, best let DNO have a look.

Let us know what they say.

Engineer54 · May 2, 2011

I think in situations such as these, it may sometimes be a good idea to ask your client if he could ask his neighbours if you could have a quick look at there earthing arrangement at the head position. It could in some circumstances, answer a lot of questions....

bodders22 · May 2, 2011

Good Idea but I'll have to try a few doors down as the next door neighbour is a 6ft transexual with a beard there aint no way I'm going in there!!

oldtimer · May 2, 2011

Yep looks like TNS now if the braid is giving you 0.14 but "who" linked it out with the neutral ? So get DNO out to resolve might be worth getting a 11497 from Screwfix as to get ready a MET.

Geoffsd · May 2, 2011

bodders22 said:
6ft transexual with a beard there aint no way I'm going in there!!

Too tall for you?

paturback · May 2, 2011

oldtimer said:
Yep looks like TNS now if the braid is giving you 0.14 but "who" linked it out with the neutral ? So get DNO out to resolve might be worth getting a 11497 from Screwfix as to get ready a MET.

sorry but whats that?

oldtimer · May 3, 2011

paturback said:
sorry but whats that?

It the MET block

bodders22 · May 3, 2011

Hi all just a quick update. I've knocked on a few neighbours doors today and checked out their supplies (yes even next doors! and I came out intact!) A few had a complete new supply that was tncs,and a couple like the house I'm on with the earth braid going into the service head, but theirs had a 16mm main earth coming out into a met, so looks like dno's converted them to tncs anybody heard of this before? I'm going to try to get confirmation tomorrow.