Fault finding in DIYers paradise

[Mike howskii]

Hi
This is my first post on any forum, I’ve been an electrician for 15 years and this fault finding job has got me stumped!
Attended a very old cottage, usual story of fuse blowin at the board. Turns out to be a 6amp 30mA RCBO, the circuit has a fluctuation neutral earth fault on it ranging from 0,15 - 3 mega ohm. Further inspection into the property found the wiring a absolute disaster! Single twin at the switch positions and single twin at the wall lights and downlights and the whole house wired on 1 lighting circuit. The advise I’m looking for, is there any logical way of finding this fault? I have done all the obvious, disconnected outside lights, inspected switches, light fittings and everything that I can get access to. The wiring in this property is a disaster and I’m unsure how to approach it on my next visit. Thanks in advance, mike

 

[Pete999]

If you have had as much rain as we have had up here over the last few months I would be looking at this too.
Has it got a thatched roof?

What furry little creatures live in cottages? Mice could be Rodent damaged cables, good luck.

 

[ipf]

First thing.... you don't say if you can reset the RCBO under no load condition?
If you can, obviously, you can narrow it down.

 

[ruston]

What furry little creatures live in cottages? Mice could be Rodent damaged cables, good luck.

There might be a band of them Pete.

 

[Lucien Nunes]

If the fault that is tripping the RCBO is the N-E fault, then it will have to be a lot lower than 0.15MΩ. If the N-E voltage were say 3.5V (half of 3% VD) then for a lower trip limit of 15mA it would have to be 3.5/0.015=233Ω, which is lower than can be accounted for by damp alone. So while it is quite likely that the cause of that bad IR is related to the tripping fault, they may be different parts of the same problem, or different problems entirely.

Even if it were L-E that was showing poor IR, it would have to be 230/0.015=15kΩ, ten times lower than you have measured so far.

 

[Squid]

Hi SWD, unfortunately the wife wasn’t there! I’ve asked him about the condition of the install and he said it was a bodger builder who owned the house before him Zzzzz usual story! He has blamed the heavy rain....after asking him a few times if he had done any work himself. Trouble is there is no accessible point to split the lighting main to pin poin the location, unless I start ripping his 18th century cottage apart! I’m at a serious loss with this one.

Tut a lot whilst rubbing chin and say it needs a full rewire...........

 

[PEG]

Hi Pete, I completely agree and I think removing floorboard to get access is the only way. As no access to the lighting main as of yet I haven’t been able to narrow down to any particular area. Frustrates me how we as electricians end of picking up the pieces of people’s bad workmanship, and have to trash peoples houses and then charge them. Removing his jigsaw oak flooring with be fun...nailed down with original blacksmith nails. Il keep you updated as back there tomorrow. Thanks guys!

Everyone has given the important bits of advice,so all that is left for me,is to say that if these fixings are flat,they will be "cut clasp" nails.

Blacksmith,or more accurately,Farriers nails,are not much use in timber,as not only are they smooth,but they have a bevel on one face,which sends them in curved. This is so they are naturally biased towards exiting the hoof at the face,and not the inner,soft parts...

Anywho,i digress...what type of wiring,is installed,on this lighting circuit?

 

[Wilko]

Hi - perhaps ramp test the rcbo?

 

[Leesparkykent]

Tut a lot whilst rubbing chin and say it needs a full rewire...........

I find the good old plumbers huff usually works

 

[Squid]

I find the good old plumbers huff usually works

Thats only because they are so fat the walk from the van to the house leaves them breathless........

 

[Timbo]

Single twin at the switch positions and single twin at the wall lights and downlights

Is this twin or twin & earth. How old is the wiring approximately?