confused..

[terry198920]

I am only a trainee ( so don't bite too much) a friend of mine called out british gas to fix his boiler.. Whilst he was there he checked the electrics.. Said the earth loop was greater than 200 ohms on the ring main and they should get a spark out asap.. So he asked could i pop down and and have a look before they call in a spark ( to see if i could see what the issue was ) it is a TT supply as far as i can tell with a wylex board rewireable fuses with separate RCD installed.. Tested the board.. 0.28ohms..PFC was 0.956kA.. Tested the rcd at 1/2.. X1 and x5.. All within limits.. Tested the socket where the PLUMBER checked and here is where i get lost.. Earth fault loop impedance Test with a megger1730.. 1st test setting was L-L 0.60.. L-N was 0.60 and the setting l-pe was 800ohms.. Is the setting L-PE the important reading yes? And whats the outcome..

 

[telectrix]

hang on. go back to basics. start with a Ze. on a TT,

 

[terry198920]

I have as i said.. Was 0.28ohms

 

[shanky887614]

hang on. go back to basics. start with a Ze. on a TT,

Then test zs directly from the board.

If its a lot lower then its probably a loose connection somewhere

(Could be a loose cable on earth bar)

 

[terry198920]

What do you mean by zs at the board? with main earth disconnected and test between live neutral earth? I always assumed ze was at origin.. Zs furthest point on a lighting point ect..

 

[terry198920]

What do you mean by zs at the board? with main earth disconnected and test between live neutral earth? I always assumed ze was at origin.. Zs furthest point on a lighting point ect..

 

[D Skelton]

Forget the earthing arrangements for a moment, if you carry out a Ze at a board and get 0.28ohms and then a Zs on a circuit fed by that board and get 800ohms then the problem is with that circuit isn't it.

All that being said, double check your readings at the board, I find it very unlikely that you will have an Ra (Ze) of 0.28ohms on a domestic TT system unless there are a good few earth rods installed or it is linked to steel reinforcement within the foundations.

 

[Octopus]

What were the readings from the other sockets on the circuit?

 

[terry198920]

Skelton.. They have recently had a new incoming supply fitted.. The reason i said tt system is because an earth is running outside to a rod.. My first thought was tns if that helps.. I should of took a picture would explain more as to why i got confused.. Im aware the fault is at the socket.. But is it as simple as finding a loose connection and tighten the earths up..

 

[shanky887614]

Forget the earthing arrangements for a moment, if you carry out a Ze at a board and get 0.28ohms and then a Zs on a circuit fed by that board and get 800ohms then the problem is with that circuit isn't it.

All that being said, double check your readings at the board, I find it very unlikely that you will have an Ra (Ze) of 0.28ohms on a domestic TT system unless there are a good few earth rods installed or it is linked to steel reinforcement within the foundations.

i don't think he was disconnecting the main earth during test, i reckon thats because of parallel paths that reading was that good.


think about it.


2.5mm--------7.50 milli ohms per metre or 0.00750 ohms OSG 7.41

 

[terry198920]

Correct i didnt disconnect the main earth for a true ZE..

 

[shanky887614]

Correct i didnt disconnect the main earth for a true ZE..

Why not? It means you will get a bad reading

 

[terry198920]

How is 0.28 a 'bad' reading if u don't mind me asking.. Or do you mean false reading?

 

[shanky887614]

How is 0.28 a 'bad' reading if u don't mind me asking.. Or do you mean false reading?

false reading I meant to say.

 

[D Skelton]

i don't think he was disconnecting the main earth during test, i reckon thats because of parallel paths that reading was that good.


think about it.


2.5mm--------7.50 milli ohms per metre or 0.00750 ohms OSG 7.41

I was coming from the angle of a loose connection on the socket circuit. I also advised re-doing his Ze as I suspect he wasn't doing it properly.

 

[KFH]

I have seen earth rods installed on TNS and TNCS systems. It can be confusing if you are not completly sure of what you are looking for. As has been said 0.28 is VERY low for a domestic TT system unless there a parallel paths e.g. shared metal water pipe with TNCS system bonded next door.

 

[MDJ]

Correct i didnt disconnect the main earth for a true ZE..

well then the ZE is not 0.28, you are getting readings from gas and water pipes, start again fella.

 

[ipf]

Confucius he say.......''don't listen to everyone at once, you'll git mixed up, go around in circles and disappear up your own backside''.
Sort out, for definite, whether it's tt, tns or tncs and then you might get somewhere with your question.

 

[telectrix]

this is TT.

 

[shanky887614]

this is TT.

View attachment 23205

Some of these guys are mechanics in there day job