ring main earth fault

[alarm man]

got a fault on downstairs ring main earth,the loop at db is 1.4 ohms but when i connect 1 leg to earth i dont get a reading to the other leg back and when both connected i get a difference of 66 ohms when reading between the earth of the socket to the adj cooker earth which is on a seperate circuit..readings are fine from any other circiut to water pipe and gas pipes etc 0.1 ohms so i think the fault is just with the downstairs ring,im only using a multi meter to test.any thoughts,other tests i can do..been out the game over 12 years

cheers alarm man

 

[johnelectrical]

let me get this right, you've taken both cpc's of a ring final circuit out, tested end to end and got 1.4 ohms, if you then connect one end to earth and test the other end to earth (don't know why you would do that?) you should of course get 1.4 ohms. not 66ohms

what was the problem that caused you to look at this circuit? are you testing the installation?
have you gone through the three steps of testing the ring?

 

[alarm man]

let me get this right, you've taken both cpc's of a ring final circuit out, tested end to end and got 1.4 ohms, if you then connect one end to earth and test the other end to earth (don't know why you would do that?) you should of course get 1.4 ohms. not 66ohms

hi john
i actually got about .810 meg with one leg connected to earth,the 66 ohms was reading the ring half way to another earth ie the sink and the cooker cpc with both ring main earths connected..ive also half fixed this fault(i think) traced to an alarm power supply in garage(might have known it would be the alarm) the power supply has a zone expander with data inputs(galaxy if anyone familliar) the pcb 0v is clamped to earth via a mouting screw,removed this screw and fault gone ive left it out and all seems fine with the alarm but ideally should be connected,the data coming down from the main panel with the 0v is fed from the upstairs lighting circ,so im guessing the fault could be with the upstairs lighting earth which i havent tested yet,so if i have a high res earth fault on the lighting circ and the alarm 0v is commoned between the lighting earth and the ring main earth would you get the 66ohm difference?has anyone had this..before i start ripping the loft to bits..

sorry forgot to say how,i was changing the sockets over in the kitchen and decided to meter the earth between the socket and the cooker,sink etc to check the readings,hence the problem i now have..

cheers
alarm man

 

[johnelectrical]

If you are getting a good earth in the consumer unit and the r2 of the (end to end) ring is 1.4 ohms.
if you have 0.81 meg between the cpc of a socket on that ring and other extranious parts in the kitchen.
i would assume one of the following, either the continuity of the ring cpc does not go round the ring but has an interconnection somewhere neerer the board, or the extranious conductive parts (cooker etc) in the kitchen are not earthed.
Not sure how a connection to earth in the alarm has anything to do with it?

If you do a long lead R2 test between the cooker and the Main earth terminal, in or next to the Consumer unit (board) it should idealy be under 0.05ohms, if its 0.8 meg, there is your answer
good hunting, John