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

 

[Squid]

Ask the client when did the issues start happening if they say a week ago then ask was any work carried out just beforehand, if they are a married couple get the wife away from her husband and whisper to her "be honest love, what did he do"

 

[telectrix]

disconnect circuit conductors from CU. estimat a rough mid point of the circuit. split circuit and IR test each section, don't forget to switch switches on/off. then, on the faulty portion, find the last light and short L-E. then test at each point for continuity. you then know which lights are on that section. then split down again till you track the fault.

 

[Pete999]

Sounds from what you have described, there will probably be a hidden JB somewhere, which will need a good coat of looking at.

 

[Mike howskii]

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.

 

[Pete999]

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.

If this is to be sorted Mike, the owner will have to put up with some disruption and possible damage to floors etc, unfortunately it's part of the job, after all you go into Hospital for surgery there are bound to be some scars left behind, maybe need to think about finding this fault on a day work basis, not an ideal way, but unless you are extremely lucky and find the problem within a couple of hours, it could take days to sort.
Are there a number of lighting circuits? have you managed to tie the fault to any specific areas in the Cottage?

 

[Des 56]

If everything visible or accessible has been inspected,there seems to be no other alternative,the circuit has to be split

Seems you may have to pick a spot likely to be where a junction would be located and start getting that access

 

[Midwest]

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.

Not strictly true, but I tend to find such readings are caused by damp or wet connections. Yesterday I was carrying out my dead tests on a new install I'd done, got similar but higher fluctuating IR figures. Track it down to the outdoor lighting points, where I'd left the cables terminated in connectors in all weathers. Quick spray of WD40, and application of 500v 'dried' them out.

OP think the only way of tracking you fault, is do as Tel suggested. Try proceeding in methodical way, perhaps start at the beginning with dead tests as for new install.

Good luck.

 

[Toneyz]

With fault finding, it is a case of narrowing the circuit down into sections.

 

[Octopus]

With any fault finding:

1. Identify what exactly is on said circuit

2. Split circuit into approx half

3. as 2 above

oh, and you need paper and pen / pencil to draw on and make notes.

 

[Mike howskii]

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!

 

[mhar]

I have just had similar, I took my assessor there this week so I could explain the situation and see if he was happy on how I was to record the results. My worst circuit (worse than the 2.5mm kitchen radial with washing machines, dishwasher, kettle, toaster etc on it ) was a large ring(ish) with half a dozen spurs plus at least 3 interconnects via concealed junction boxes. I disconnected everything on the circuit, joined l&n on one of the tails and went round every point to see where I had continuity. I was expecting to find just one point initially but no, there were three and not where I was expecting them.
My intention was to make it into two 20A radials but there was no single point where I could split and have no interconnections between the two. I had to leave it with a single 20A ocpd with non standard circuit warnings on the busbar cover, the cu and the cert.
Took a while!

 

[westward10]

Old property, look where the floorboards have been up before rather than pulling ones that have been down since year dot.

 

[Pete999]

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!

Think the first step to locating any JBs would be to look for any flooring that looks like it has been disturbed, or try and narrow it down to where you think might be a good place to make joints, (no not spliffs)

 

[ruston]

Not strictly true, but I tend to find such readings are caused by damp or wet connections. Yesterday I was carrying out my dead tests on a new install I'd done, got similar but higher fluctuating IR figures. Track it down to the outdoor lighting points, where I'd left the cables terminated in connectors in all weathers. Quick spray of WD40, and application of 500v 'dried' them out.

OP think the only way of tracking you fault, is do as Tel suggested. Try proceeding in methodical way, perhaps start at the beginning with dead tests as for new install.

Good luck.

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?

 

[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...........