how to find earth leakage in light circuits

[ericmark]

If the fault was a borrowed neutral there would be two circuits which are not RCD protected, since only one we can discount that. Other cause is where electronic switches are fitted which need a neutral, and some one has used an earth instead, so I would look for any dimming switches.

The next is the fixing screws in the switch pinching the neutral, this needs a tester, and removing all switches, there are two ways to test, one is use an insulation tester the other a clamp on ammeter both the ones I show cost £35 when I bought them, and need some skill to use them, and also likely some time, what we need to do as electricians is:-
1) Turn all lights off and remove bulbs, disconnect neutral in consumer unit, and test to see if line or neutral, this can half the tests further on.
2) Guess approx half way, and test both sides.
3) Guess approx half way in faulty side, and again test both side.
And so on, one can be lucky, but is can also take a long time.

I did it with daughters house, and found a fixing screw shorting on a neutral wire where the installer had caught the installation when stripping with a knife. Mothers house I aborted as found the wiring was rubber, and simply needed a rewire, and it was better not to disturb until ready for a rewire.

The problem is the bathroom. The use of plastic pipe can result in the bonding being broken, and it must either be fully bonded or RCD protected, and if neither fully bonded or RCD protected it will fail an EICR.

As said putting the clamps around the meter tails you can see the total leakage. I find this is a good start point, my tails show about 22 mA total leakage, which over 14 RCBO's is not a problem, but not really going to work with just two RCD's. However your paperwork says zero so it would seem a direct short rather than overall leakage.

I suppose first thing to look at is any outside lights, but one would have expected the electrician to have looked at that.

 

[Murdochcat]

You are obviously not familiar with the borrowed neutral on some stair lights.

Ok, my thoughts were incorrect.

Yes 100% - your thoughts are incorrect - very familiar with borrowed neutrals

 

[Zehroni]

1) Turn all lights off and remove bulbs, disconnect neutral in consumer unit, and test to see if line or neutral, this can half the tests further on.

many thanks for your detailed instruction. can you elaborate more on the above please. when I disconnect the neutral from the CU the live will be still connected as well as the earth. What does " line or neutral mean" ?

 

[crystal ball]

many thanks for your detailed instruction. can you elaborate more on the above please. when I disconnect the neutral from the CU the live will be still connected as well as the earth. What does " line or neutral mean" ?

As Eric mentioned, do you have any outside lights?

 

[Zehroni]

As Eric mentioned, do you have any outside lights?

my next visit to the property is this Saturday and will check. assume there is what shall i do? just disable it or look inside to see if there is connection between Neutral and Earth? or what else?

 

[Harry Bloomfield]

my next visit to the property is this Saturday and will check. assume there is what shall i do? just disable it or look inside to see if there is connection between Neutral and Earth? or what else?

It could be as simple as moisture/water, getting into the outside light and that would be enough to cause an RCD to trip/fail an insulation test.

 

[ericmark]

Lives can be above ground potential or at some point bonded to ground, and when bonded to ground they are called neutral, however where bonded can be some distance away from where being used and the current flowing can cause them to be above ground at the point of use, so are still called live, so we call the wires not bonded line wires. So line and neutral are both lives.

However since neutral is bonded to earth at some point, to test the insulation the neutral has to be disconnected, and MCB's don't isolate, the RCD will and the Isolator will, but not the MCB.

You don't want to be testing all circuits so either you remove the neutral wire at the consumer unit, or in your case, turn off both RCD's and the Isolator as only the lights are supplied from non RCD protected then you could test without opening the consumer unit.

But likely best to disconnect lights but do remember the tester uses 500 volt, so not safe to do tests with children around, and in the main to be safe it needs two competent people. It is so easy to make a mistake, and I don't really think it is a DIY job.

 

[crystal ball]

I get called to lots of RCD tripping problems and would say 75% are caused by water ingress on outside fittings. either sockets, lights or junction boxes

 

[flameport]

one of the ways I would start Tshoot the issue is to move from the far right MCB to the fifth from left RCBO, switch all then lights off and then switch them one by one and see which one trip the RCBO. do you think that would work?

The installation has defects which should have been fixed 3+ years ago.
That consumer unit installation is a pile of crap.

If your tenants are still living there, those problems need to be fixed immediately by someone competent to so do. That isn't you.
Stop tampering with things you do not understand as you are putting your tenants at risk of electric shock, fire or worse.

 

[crystal ball]

The installation has defects which should have been fixed 3+ years ago.
That consumer unit installation is a pile of crap.

If your tenants are still living there, those problems need to be fixed immediately by someone competent to so do. That isn't you.
Stop tampering with things you do not understand as you are putting your tenants at risk of electric shock, fire or worse.

Why is the CU a pile of crap?

 

[Zehroni]

The installation has defects which should have been fixed 3+ years ago.

called few locals and the suggested it is a fault finding issues and may take long time to find and fix. however, most recommended rewiring is the way forward but they can not do it while tenants are there.

That isn't you.
Stop tampering with things you do not understand as you are putting your tenants at risk of electric shock, fire or worse.

do not under estimate people ability. the same thing happed in one of my university friend house in Manchester where the light RCBO kept tripping. The way we find the faulty wire is we switched every light off, then we switched them on one by one until we got to the bathroom. the piece of wire between the master bedroom and the bathroom was damaged by rats. the new wire was connected the old one then pulled from one side to until it came out from the other side and that how we solved the problem and all over the phone as i am living in the southwest. I am hoping this case will be similar. I have not done a lot of testing on this issue yet as I was hoping for the tenants to move out but they are not. However, I thought no harm in seeking the advise of decent, positive professionals in this forum before I start.

 

[flameport]

Why is the CU a pile of crap?

Have you looked at the certificate images and the photo of it?

 

[flameport]

called few locals and the suggested it is a fault finding issues and may take long time to find and fix.

Feeble excuses.
Fault finding on a circuit does not involve rewiring, and neither does it matter whether people are living there or not.

You have a legal duty to ensure the property is safe, which includes the electrical installation in it.
Currently it isn't. Deal with it.

 

[crystal ball]

Have you looked at the certificate images and the photo of it?

Not talking about the cert, what in particular about the CU?

 

[Zehroni]

Feeble excuses.

do you have a technical knowledge that add value to this issue?