Todays pain in the Butt.

[Bez]

Cu change today, nice and straight forward, posh new tails, new 16mm earth, Bonds to gas and water, 10 way dual RCD MK for an old Wylex rewirables jobby. Easy, NOT!

Did all the usual dead tests with no traumas, popped it all together and energised, hey presto, downstairs lights tripping RCD, ****!

Now I took the trouble to put both lighting circuits on the same side of the board due to past experiences with borrowed neutrals and all that mullarky, so was starting to get thoughtful by this point.

It all meggered out ok, so checked outside lights, (had em full of water before now!) Not them, ****!

Customer saw me head scratching and offered a brew, gratefully accepted, when a strange thing happened. On went the kettle, Out went the RCD again.

Now the ring was on the previously faultless clean side of the board, yet it tripped the RCD on the lighting side.

I'll cut to the chase, Wall lights were fitted some years ago and I'm thinking they've borrowed a neutral from the ring. I was running out of time for any further investigations so have left the lights on PME, all other cicuits on RCD's, for tonight and will return in the morning

What d'ya reckon, It's a teaser!

Bez

 

[Megaohm7]

Seems a strange one that you have done the dead tests before fitting the new CU. What was the IR readings , did you check each individual circuit for insulation resistance?

 

[Bez]

Seems a strange one that you have done the dead tests before fitting the new CU. What was the IR readings , did you check each individual circuit for insulation resistance?

This is what leads me to believe it's a crossed/borrowed neutral.

R1 + R2 not affected

IR not affected

I'm thinking that when I go back in the morning, disconnecting the sockets neutral in the board will clear the tripping, then I can set to work on some floorboards!

 

[Megaohm7]

I can see your thinking as it's affecting the other neutral bar. I wonder what surprises you will find under the boards??. I have a CU to change myself in a bungalow. Should be straight forward but who knows what will happen. I hope the fault will be a quick one to find.

 

[Chr!s]

Isolate the two neutral bars, test between the two, if theres a short then you know theres a borrowed neutral, then start to disconnect till fault clears, you will then have your faulty circuits.

 

[Robin Spark]

Are you getting paid for the extras Bez?

If not just put that ring on same rcd as the lighting then the rcd will be ok.

if you are getting paid extra to sort the faults then proceed to rectify and makje circuits all good

 

[Bez]

Are you getting paid for the extras Bez?If not just put that ring on same rcd as the lighting then the rcd will be ok.

if you are getting paid extra to sort the faults then proceed to rectify and makje circuits all good

Told them I will give them a couple of hours in the morning as they've looked after me, tea, sarnies etc.

After that the meters running!

I did make it clear at the outset there may be faults highlighted, and that it would incur extra cost.

 

[Robin Spark]

Tea, sarnies and nice customers...always worth keeping for the future

 

[Ali]

I'm always amazed that so many customers don't realise that the odd cup of tea and a bit of friendliness can go a long way. It's not that we demand it, it's just that it puts us into a much better frame of mind when they ask us for something for nothing (and I don't think I've ever met a customer that hasn't asked).

 

[sellers]

Isolate the two neutral bars, test between the two, if theres a short then you know theres a borrowed neutral, then start to disconnect till fault clears, you will then have your faulty circuits.

Sorry plumber but that is not a borrowed neutral. A borrowed neutral is taking the live of one circuit and using a neutral from another. Your method will only show if 2 neutrals of 2 different circuits are connected somewhere.

To test for a borrowed neutral the best method is to switch all lights into the on position. Leave loads plugged in on socket circuits.

Then for example take downstairs lighting circuit neutral out of the bar, and check for continuity between the line and the remaining circuits in the neutral bar.

If you get continuity you will be reading through the lamp where the neutral has been borrowed from. Disconnect each neutral until the continuity is lost and there is the circuit you have borrowed from.

 

[Chr!s]

Hi Sellars

Sorry plumber but that is not a borrowed neutral. A borrowed neutral is taking the live of one circuit and using a neutral from another. Your method will only show if 2 neutrals of 2 different circuits are connected somewhere.An upstairs light is fed a line from the downstairs circuit, the neutral is borrowed from the upstairs ring circuit, agreed?

I wasnt trying to define what a borrowed neutral was.

To test for a borrowed neutral the best method is to switch all lights into the on position. Leave loads plugged in on socket circuits.

Then for example take downstairs lighting circuit neutral out of the bar, and check for continuity between the line and the remaining circuits in the neutral bar.

If you get continuity you will be reading through the lamp where the neutral has been borrowed from. Disconnect each neutral until the continuity is lost and there is the circuit you have borrowed from.

Ok, my method wasn't as detailed and specific as it should of been. :z

Isolate the two neutral bars, test between the two, if theres a short then you know theres a borrowed neutral, then start to disconnect till fault clears, you will then have your faulty circuits.

Ill add, ensure lights are on, all mcbs are on, isolate main supply, place a link between L-N on each side of the board, test between the two neutral bars, disconnecting the circuits via mcb till fault clears.

 

[sellers]

MCB's should be left off otherwise you will not get a true reading of which line is connected to which neutral. If you leave them on, you will be reading through all lines. I'm not familiar with the method you mention of using a link?

 

[Chr!s]

MCB's should be left off otherwise you will not get a true reading of which line is connected to which neutral. If you leave them on, you will be reading through all lines. I'm not familiar with the method you mention of using a link?

If all the mcbs are on, if i test across both neutral bars if there is a borrowed neutral this will show, agreed?

If i start to isolate the circuits one by one, when the faulty circuit is isolated there will be no short between the two neutral bars

 

[sellers]

I can see how that works, if using a L-N link, but it won't work without.

 

[Chr!s]

I can see how that works, if using a L-N link, but it won't work without.

My apologies, i wasn't very clear.