No earth loop

[jparker3007]

hi guys
i went to a customers today to do a mains change, it was a tn-s supply, the earth was to a block but there was none to the db. so while i was changing the db i rectified this with a 16mm. on doing the earth loop test with my megger it was showing voltage between L/E but wouldnt perform test. testing the socket beneath gave me an earth loop of 2.03 ohms??????

im guessing ive got a dodgy earth so what i was going to do was change it into a tn-cs arrangement, have any of you come across this before?
thanks

 

[welsh spark]

hi mate,
I use a megger and if it is on no trip loop setting you will need to a neutral otherwise the tester wont test i test ze on the loop hi setting wich dosent require a neutral on the other hand the reading on your socket of 2 ohms sounds like its your parralel paths eg gas and water pipes giving you a reading if this is the case you have no earth and need to phone the useless dno people hwo will probably tell you to convert it to a tt as they are to lazy or busy to sort it out (Rant over) hth welsh spark

 

[jparker3007]

hi welsh spark
i disconnected the earth and tested at sheating, i was gettin 240v but wouldnt test earth loop on hi. so cant be parallel paths im guessing its the dozt **** at other end

 

[welsh spark]

very strange there must be something there as your reeding 240 between line and earth unless its just not good enough. Have you tried a different tester just to make sure your tester isnt faulty just a surgesstion as these things have happend to me before let us know how you get on

 

[jparker3007]

going back at the weekend to start job and sort this out ill let u know pal thanks

 

[jparker3007]

went today changed it over to tn-cs 0.10 ohms at db now, everybodys happy lol

 

[parkerbloggs]

i didn't think you could just change the earthing arrangements of an installation from tns to tncs just like that.A change to TT is ok. Is the supply cut out and supply cable of the installation for tncs?

 

[mrloy99]

i didn't think you could just change the earthing arrangements of an installation from tns to tncs just like that.A change to TT is ok. Is the supply cut out and supply cable of the installation for tncs?

agree.!!!
Normally on a tn-cs the neutral is earthed at numerous points on the way back to the supply transformer......(pme-protective multiple earthing) whereas on a tns system this is often not the case.
Also I'm not quite sure where you have performed this tn-csing as usually this would entail the changing of the supply authorities end box to facilitate the link,AND they would sometimes install an additional
spike...
A similar thing happened to me in the past when I was just starting out(forgetting to test untill too late)The supply authority wouldn't reconnect me as there was a crap supply earth,and their old cast iron end box wasn't bonded and they wanted me to TT it,so I'd to come back to the job the next day with my 2 rcds and had to alter the layout...but one of the trips was faulty and I'd to go to wholesaler to change it,and I got back in the afternoon to find the supply authority geezer had been and all AND PME'd it.

 

[sparks1234]

Correct me if I am wrong but that does sound dodgy.

 

[mrloy99]

hi guys
i went to a customers today to do a mains change, it was a tn-s supply, the earth was to a block but there was none to the db. so while i was changing the db i rectified this with a 16mm. on doing the earth loop test with my megger it was showing voltage between L/E but wouldnt perform test. testing the socket beneath gave me an earth loop of 2.03 ohms??????

im guessing ive got a dodgy earth so what i was going to do was change it into a tn-cs arrangement, have any of you come across this before?
thanks

Perhaps it already was TT,hence the reason that the 16mm link was left out and the reading at the socket was 2.03ohms....Perhaps there was an earth connection to your earth spike from your existing consumer unit..This could have been in the form of an old green cable as small as 6mm which I believe would still have been acceptable....But there would have been some kind of main trip (rcd)???or elcb.

Just because your supply was underground does not automatically exclude the TT arrangement.
It might go up a pole round the corner or perhaps there has been a previous repair done in the street -external to your installation. In theory the problem with just sticking a link in from neutral to earth could mean that if the neutral were to become disconnected further up the line,and if your water supply were to be changed to plastic,all your metalwork,COULD become live(if there were no earth electrode installed)..............on a tn-cs the neutral is connected to earth at neumerous positions
often underground and unseen.

 

[AA410]

Bit concerned are we as the people on the ground aloud to play with the suppliers instalation ?????

 

[jparker3007]

i did this under instruction from an old spark working at the yedl, apparantley it happens all the time

 

[jimsky007]

my concern would be if the neutral is lost going into this supply due to an underground fault then return currents would be via bonding conductors?? TN-c-s Ze should be a max of 0.35 ohms this can be checked accross the phase conductors coming in TN-s Ze max 0.8 ohms

 

[scotsparky]

sounds like it was an origional TT and the Ze you were reading was the supplimentary bonding through pipework and structural steel. Did you try and take a true Ze or was it your ZE(D.B ) that was 2.03ohms? I have seen this a few time and if your lucky the cable head hasw an unsed earth bar in which case supply authority will change as they have misrepresented main earthing arrangement available.

 

[jparker3007]

when i was testing the db it was showing voltage between L + E 240 but wouldnt do loop test, the 2.03 was from a temp socket under db. it did baffell me a bit id admit but everyone ive spoke to about it who came across same problem they changed it to tn-cs

 

[BillR3]

I would go back immediately and disconnect your made up tnc-s system. Revert it to a TT system with a newly fitted earth spike and cover the installation with a 61008 device as you cannot just go around making up combined neutral and earth systems.
BillR3

 

[scotsparky]

if it wass tt and you were getting an eath path through the water,strucural steel ect you would get 230v try it agian one all main bonding has been disconnected i would be suprise if there was an eath.
Call supply authority see what system they have installed if they say tn-c-s thenits ther responsibility to provide an suitable earth terminal.

 

[andekoch]

I would not convert to a TNCS. It sounds like it is a TT with the earth spike just not visible. If anything convert to a TT. As said before due to the construction of TNCS (PME) the dno is the one who does the change, it is (should no be) a simple connection in the domestic premisis.

A quick check of the incomming cable in the fuse block will tell you if it is TT or TNS or TNCS. TT generally will not have 'armour' and will have 2 cores, TNS will have steel armour or lead sheath and 2 cores, TNCS will have a single core with the 'armour' being half copper and half steel.