Fault Finding Problem

[philly4321]

Hi All,

Been out to a job last week as the RCD was tripping. Narrowed this down to the ring main circuit. The house is a three bedroom house with only one ring main servicing the entire house.

Continuity test on ring are within parameters - L-L - 0.56 N-N - 0.58 E-E - 0.94

I then put the circuit on the non RCD side and it energised fine no issues, Zs tests on sockets were also fine.

I then undertook an IR test and the results were 0.00 for L-N, L-E & N-E, I have never come across this before and has left me puzzled. All tests undertaken using Megger 1552 MFT.

The house has been rewired by a keen amatuer at some stage and I believe the problem lies in one of the numerous spurs off the ring.

I am going to be relacing the consumer unit as it has seen better days, RCD ramp test was only 15mA, however with the readings on the IR test I am stumped. I have taken off all socket faces and checked cabling and all is well behind sockets.

Usual suspects such as any DIY, nails for picture etc have been ruled out. Dishwasher was causing problems about 6 moths ago on hot wash only but this seems to have been rectified.

Going back tomorrow and will split each socket and spur in turn to see if I can locate fault, but at moment feels like im stabbing in the dark. House covered in laminate flooring top to bottom with anice shiny fitted kitchen, so minimum disruption is a neccsisty.

Any guidance or similar experiences would be most welcome.

Thanks

 

[nickblake]

Think you'll find the problem is a trapped neutral in one of the sockets , as for the low readings on the other parts of the circuit thats probably due to some thing being left plugged in ,quickest way to find out if its a trapped neutral do a continuity test between N and E see if you get a reading if so get looking and check all sockets could also be a faulty socket or even an animal cat dog etc peeing over the socket see that happen loads of times

 

[Deleted member 9648]

Given your IR results there are clearly still loads connected....find and disconnect any loads,ensure you are testing a completly 'clean' circuit.

 

[gamblor6]

sounds like a neutral earth fault to me. if stuff was plugged in those ir readings would come up. split the ring at the db, also split it at a point mid way. this way the fault will show up on one side, work backwards from the mid point to the db and you,ll find it. be aware it may be 2 or more faults and this could show up on both sides when split.

 

[philly4321]

Thanks guys, forgot to mention, nothing plugged in to any of the sockets as this was the first thing I checked, results still same also disconnected all spurs and repeated with same results.

I have also checked all cabling in back of all accessoires and thats fine, will result to changing then on return visit.

 

[nickblake]

youve not got an outside socket thats full of water have you always a possability

 

[ryan1]

is the central heating wired off ring main some times missed.if IR was dowm l-n mcb would trip

 

[philly4321]

There are no outside sockets and the boiler is on its own dedicated circuit, as this was a favourite for me also.

 

[ryan1]

with circuit down on IR L-N and not trip mcb when on non rcd side it say to me something plug in somewhere.any outside lights

 

[philly4321]

There are no outside lights, I did find an internal light in dining room that was wired off the ring main, I disconnected this so it is permissible that there may be others even though there are 2 seperate lighting circuits at CU!!!!

 

[Ponty Massive]

Had that a few times, outside light spurred off the ring with water in.

 

[Octopus]

I was fault finding an issue recently and eventually I located a faulty socket. Took a few hours of spliting and extendind to identify the issue. Very tedious and finally very rewarding with a very happy customer.

 

[Ponty Massive]

Does feel good when you find it. Had one last week where a fish tank had a very slight leak and water had found it's way into a JB under the floor boards.

 

[SimpleSimon]

Aerial booster in the loft?

 

[ryan1]

worth checking. have a look in the loft as well for tv amps ect must be something somewhere m8