loop test problem

[Acer]

Recently got a call from a friend who, whilst having annual boiler check, was informed that the earth loop reading was high. So I said I would have a look. The installation is TT so I had a look for earth rod and found that the earth wire ( old 2.5mm imperial equivalent) had been chewed through and was no longer connected to rod. Replaced earth wire with 10mm back to connection block where a 16mm went on to fuseboard. Then started to do test...disconnected main earth in board and put meter probes across incomer..immediately saw something not right as voltage on meter only 167v and meter warning lamp lit ( meter is Kewtech KT61 recently calibrated)...stopped test and reconnected main earth then did loop test at socket outlet and got 1142 ohms @ 246v..

The property was rewired on a council grant about 18yrs ago and they have left the original earth trip connected ( it must be about 40-50 yrs old) and just connected their new 16mm earth to the original earth wire which went to old trip. Could this old trip be causing some sort of problem now??....The mains arrangement is rather odd in that the cutout and meter are separated by about 8 metres of old 10mm imperial equivalent two core sheathed cable with VIR insulated cores. The surrounding properties are also TT overhead supplies..could there be a neutral/earth problem at supply transformer??...Any advice would be much appreciated...

 

[telectrix]

check your L-N volts. if that is correct at 230 - 240v, then the 167v to earth rod meand that the rod and/or connections need replacing. a 3'twig is no good. use at least 2 screwed together rods, at least 3'from building. go deep, then check again. you shoiuld get the right voltage and a better Ze.

 

[sedgy34]

Recently got a call from a friend who, whilst having annual boiler check, was informed that the earth loop reading was high. So I said I would have a look. The installation is TT so I had a look for earth rod and found that the earth wire ( old 2.5mm imperial equivalent) had been chewed through and was no longer connected to rod. Replaced earth wire with 10mm back to connection block where a 16mm went on to fuseboard. Then started to do test...disconnected main earth in board and put meter probes across incomer..immediately saw something not right as voltage on meter only 167v and meter warning lamp lit ( meter is Kewtech KT61 recently calibrated)...stopped test and reconnected main earth then did loop test at socket outlet and got 1142 ohms @ 246v..

The property was rewired on a council grant about 18yrs ago and they have left the original earth trip connected ( it must be about 40-50 yrs old) and just connected their new 16mm earth to the original earth wire which went to old trip. Could this old trip be causing some sort of problem now??....The mains arrangement is rather odd in that the cutout and meter are separated by about 8 metres of old 10mm imperial equivalent two core sheathed cable with VIR insulated cores. The surrounding properties are also TT overhead supplies..could there be a neutral/earth problem at supply transformer??...Any advice would be much appreciated...

these old trips are to be taken out if you think there is danger to the property you must report it to the dno so they can satisfy themselves with your findings.

 

[Acer]

thanks for your advice....checked the L-N volts with Fluke..got 240v. Have looked at previous BG boiler check reports and the high loop problem was first flagged up last year so I will assume that before that the readings were within acceptable parameters....however it could be that the readings relied on the water and gas bonds...if either of these have been changed in recent years then perhaps that could also be explanation....another spark has suggested an earth fault at the supply t/x...the 'client' does'nt have much dosh so before I start putting more rods in I need to be more certain what the problem is....

 

[telectrix]

on a TT system, it doesn't rely on DNO earthing. all you get is L and N. your rod is the only earth. your first job is to fit a decent rod. then go from there. you will need all circuits RCD protecting. remove that old elcb.

 

[snowhead]

I'm surprised BG haven't insisted on a full rewire and C.U change, before turning the boiler back on. They employ highly trained (salespersons) engineers, you know.

 

[Acer]

the board is a Crabtree starbreaker and has 30ma rcd as main switch...repositioning a new rod is an option I am considering and the only one that makes sense so far but as I said before I want to eliminate all other possible causes first....the distance between the board and suitable rod location is considerable and the customer has very limited dosh...thanks again for advice..

 

[Acer]

The house was rewired on a council grant some 18yrs ago...but they cut a lot a corners in doing so...they were told it was just a bungalow..and it is but the largest one I have worked in..most rooms have only 1x 13amp double...they reused the porcelain pull switch in bathroom..did not upgrade main earth cable nor remove the elcb....having looked at several of the BG service reports it would appear that this problem is only a couple of years old.

 

[adamh]

i read on another post that they check the earth usuing a plug in indicator not a dedicated efli tester , so if they didnt have these at the time it wouldn't be on their reports, and as every1 else has said with it being a TT and you getting 240V accross phase and neutral the only issue you have is with the Earth rod. When checking efli, the p.d. accross L N isn't measured.

You have replaced the main earthing conductor with 10mm so you should have continuity on that, so it just leaves the rod what are you getting for Ze?

 

[Acer]

The loop reading at socket outlet was 1142ohms......however when I attempted the ze test at board the L-N was only 167v on tester and warning light came on so aborted test..I am going back tomorrow and hopefully will get to bottom of it..

 

[adamh]

during the Ze your checking Line and Earth , the neutral only comes into it for a no trip earth loop if checking after the elcb. unless you have a 2 wire no trip test meter.

 

[Acer]

Went back to job today..still got same weird results..but managed to get more on installation history..the water main had been replaced with plastic and the gas meter had been moved but earth clamp not reinstated, on top of that there had been alterations some time ago to the overhead configuration.. Went to neighbouring property and saw that he had managed to get pme... Anyway spoke to another spark mate and he came and did tests with his equipment and his meter wouldn't perform ze test either..he was using Megger whilst mine is kewtech..the problem seems to be on supply side so will be contacting supply company..

The customer had kept all paperwork going back years...BG had only been servicing boiler for last 4 years..the previous company did not check earth loop as part of their checking so it is very likely that the high loop has existed for sometime...Also, before going back to job I phoned Kewtech technical bod as I needed some sort of explanation as to why warning lamp lit up when attempting ze on rod...I didn't want to damage tester..bod was firmly of the opinion that the problem was external to the installation..as my colleague confirmed when he carried tests with his tester...