Ring Main Fault

[Jimmyb]

hi all, Got called to a job tonight, ring main blowing fuses, did the usual and disconnected all equipment and did insulation test and got a result 0.01 Meg ohms between between live to earth, and live to neutral, so then did a continuity but got open circuits on all test, i joined live&neutral together and insulation tested it again to check there was nothing i missed to disconnect even thought I'm 100% sure there was nothing, i have to back tomorrow to try and sort it out but could any give me any pointer as i could understand why the open circuit.

thanks.

 

[nickblake]

is it blowing a fuse mcb or tripping the RCD , did you do a ring continuity , and its open circuit or a continuity of the conductors to earth ie live to earth continuity , do a live to earth continuity see if you get a reading if you do test at each socket and see where you get the lowest reading and then check that socket , if the fault is located re do the IR but do it a 250 volts first

 

[Jimmyb]

it the old push in fuses, i did a continuity of conductors to earth and it was open circuit on all legs joined (Live & Live joined, Netural & Netural joined to earth) but 0.01 Meg ohm on insuation

 

[Sparky Ninja]

Have you done any tests between line and neutral with a low reading ohmeter?

 

[Jimmyb]

yes and it was open circuit (>2000) but as said before 0.01 meg ohms when insulation tested

 

[Sparky Ninja]

Well maybe it falls between 2,000 & 10,000 ohms?

I doubt it though.

 

[Risteard]

Well maybe it falls between 2,000 & 10,000 ohms?

I doubt it though.

0.01 Megohms is, as you say, 10,000 Ohms. If reading to two decimal places then anything above 0.005 Megohms would read 0.01 Megohms and anything below presumably 0.00 Megohms. If that assumption is correct then it is reading at least 5,000 Ohms between line and cpc or whatever was being measured..

 

[Jimmyb]

found fault, water in jb outside. phew

 

[Sparky Ninja]

Well done.

Reminds me of a nuisance client I had last year where I carried out a periodic and had the same thing. He was an electronics engineer and refused to believe you could have an open circuit and a below 1 megaohm at the same time. I ended going back to redo the tests with him watching, turned out to be water penetration in an outside light (it was snow at the time). He withdrew his complaint.

 

[Jimmyb]

thanks

snow can cause so many troubles

 

[telectrix]

thanks

snow can cause so many troubles

if snow can close half the schools, bring the country almost to a grinding halt, who are we to compain about an occassional trip caused by snow in the electrics

 

[Jimmyb]

too right, money in the pocket tho, at least there some good points to snow