UK Earth leakage issues.

[Edward67]

Hi all. Im looking for some help regards a massive earth leakage issue in a new i installation
Its a little more complicated than this but its hard to explain. New board 16 way tails splits due to old board still i operation for new few weeks. Large 4 bed house. Pme system. Earth verified bonding in place.
My main issue appears to becoming from a newly installed lighting circuit. It consists of downlights and standard pendant type lights and a bathroom fan and some wardrobe lighting.
I have tested the circuit R1 and R2 all fine 1.68. IR 999 so all fine there.
My first thought was damaged insulation causing but how can this be when IR is fine.
I have inspected whole circuit multiple times but nothing obvious.
Now here is what i dont understand. If i clamp at the meter i get 180 to 400 milliamps rapidly up and down where as my RCD is not tripping?
But if i test the rcd at a socket it tests fine.

So at this point I'm thinking WTF. Alot of workmen have been on site. Plasterers carpenters etc.

This is where things get stranger. I decide to go to first switch disconnect all seems fine test incoming feed 240v. I go to second switch and disconnect. So all i have is the feed from first switch. I test here but discover i am getting voltage reading between my incoming cpc and the light cpc even though they are completely separated.
Induced voltage? But why. We dont normally check voltage on the cpc so am i looking at something normal.
At this i put circuit back together go to the board. Out of interest i pull the circuit cpc (yes circuit was live so dont crucify me) and find if i link to main earth terminal i see 100v. Ok i put it back in then things are at same potential so it disappears.

So I asked an electrician with 20 years experience to come have a look. He is also stumped. I have not tested the full installation yet so maybe its fault affecting my circuit?

Thoughts helpful. If thos makes any sense at all.

 

[pc1966]

Borrowed neutral?

The leakage is not always to earth, it could be to another circuit's return!

 

[radiohead]

I think it's an induced voltage. If you have verified the earthing system,R1+R2, IR, polarity and Zs of the final circuit along with satisfactory operation of the additional protection .....put it all back together and move on. You'll do your head in.

 

[Edward67]

I think it's an induced voltage. If you have verified the earthing system,R1+R2, IR, polarity and Zs of the final circuit along with satisfactory operation of the additional protection .....put it all back together and move on. You'll do your head in.

Thanks for reply. I more concerned with the huge leakage through main earth. I understand my rcds are fine just like to know the real cause. I never put my clamp round live and neutral of each rcd to verify the leakage through them so that will be next step. Was wondering if its travelling into the building and not out.

 

[pc1966]

Did you clamp just L&N of the supply? Of the circuit in question?

If the clamp included E then it could well be some current cirulating via bonding to gas/water/etc.

 

[Edward67]

Did you clamp just L&N of the supply? Of the circuit in question?

If the clamp included E then it could well be some current cirulating via bonding to gas/water/etc.

Hi thamks for reply. No i clamped solely the main earth on its own. My thoughts is it voltage external causing it as you say from bonding or incoming neutral. Its pme system. Think the ze was around 0.3.
Never come across this before but more i read it does happen.

Thoughts appreciated.

 

[plugsandsparks]

clamping the earth is a waste of time and energy, all you are seeing is other users loads. Just clamp the LN tails

 

[Edward67]

clamping the earth is a waste of time and energy, all you are seeing is other users loads. Just clamp the LN tails

I will do. I borrowed it as i didnt have one.
Could you explain with little more detail why if i clamp mine at home either live and neutral or just main earth i get the same 14ma. Trying to improve my understanding.

 

[plugsandsparks]

Its easier with a drawing but its down to how PME is connected at each property. Every load on the local PME will put additional potential in the neutral line as the load increases, this can make all the earth connections a viable route as an additional path for Neutral return to TX. So lets say next door puts the kettle on, 12.99Amps go down their neutral and 0.01amps finds a different path via all the connected earth systems including yours.
If you want to see some spectacular earth currents, try a commercial or industral site where they are made of girders into the ground and all the steelwork is bonded to earth.
Your house , if its PME, means you are not a viable route for load on the PME system or you are the only house on the TX.. lol

 

[Edward67]

Its easier with a drawing but its down to how PME is connected at each property. Every load on the local PME will put additional potential in the neutral line as the load increases, this can make all the earth connections a viable route as an additional path for Neutral return to TX. So lets say next door puts the kettle on, 12.99Amps go down their neutral and 0.01amps finds a different path via all the connected earth systems including yours.
If you want to see some spectacular earth currents, try a commercial or industral site where they are made of girders into the ground and all the steelwork is bonded to earth.
Your house , if its PME, means you are not a viable route for load on the PME system or you are the only house on the TX.. lol

Thanks for reply again. I underatand what you are saying and before today i have never really considered it because i have never clamped a sole main earth.
My conclusion is the leakage is as you say because my RCDs are fully operational. So this 225 to 400ma i think is incoming.
To try to settle it I'm going to clamp the rcds separately.
This seem logical?

 

[plugsandsparks]

Yep, the RCDS are only comparing L&N if they are too different the RCD trips. All the additional earth currents do not go through the RCD they are simply travelling up the incoming Neutral across your MET and onto the Gas pipe, water pipe, steelwork, anything stuck in the ground etc.

 

[Edward67]

Yep, the RCDS are only comparing L&N if they are too different the RCD trips. All the additional earth currents do not go through the RCD they are simply travelling up the incoming Neutral across your MET and onto the Gas pipe, water pipe, steelwork, anything stuck in the ground etc.

Thank you for your help. Will retest and get back to you with result.

 

[Gary latto]

Still learning so interested to follow if that's ok cheers

 

[Edward67]

Still learning so interested to follow if that's ok cheers

No problem. Keep you updated

 

[Lucien Nunes]

Out of interest i pull the circuit cpc (yes circuit was live so dont crucify me) and find if i link to main earth terminal i see 100v

This isn't really a useful test but 100V is a perfectly reasonable result for induced voltage. One side of your meter sees earth, the other sees a floating length of CPC that isn't connected to any terminal of the supply. But there is capacitive leakage into it from nearby line conductors, and leakage out of it to nearby neutral conductors and earthy objects, and this forms a potential divider. The actual voltage, often between 1/4 and 1/2 of line voltage, doesn't signify very much other than that there are some live cables around the place.

If you had measured the current from the disconnected CPC to earth, you would probably have found that the leakage is tiny, a fraction of a milliamp.

 

[Edward67]

This isn't really a useful test but 100V is a perfectly reasonable result for induced voltage. One side of your meter sees earth, the other sees a floating length of CPC that isn't connected to any terminal of the supply. But there is capacitive leakage into it from nearby line conductors, and leakage out of it to nearby neutral conductors and earthy objects, and this forms a potential divider. The actual voltage, often between 1/4 and 1/2 of line voltage, doesn't signify very much other than that there are some live cables around the place.

If you had measured the current from the disconnected CPC to earth, you would probably have found that the leakage is tiny, a fraction of a milliamp.

Thanks for response. .
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Ok. I went and purchased a clamp meter today. For a little test I clamped my main live and neutral 10ma. Out of interest I clamped the main earth. Same reading. 10ma.
So I opened up my board and only cable in that I could easily clamp was my alarm cable. So I clamped live and neutral 130ma approximately. I then clamped the cpc on.its own. 1ma.
Could one of you kind people explain this?
Guessing its electronics in some form.

Also back onto my original large earth leakage issue. How common is it for tncs to be affected with earth leakage from sources external to the property:?
As I say it all points to that conclusion due to the rcds working fine within the installation but just find the issue disconcerting.
Also would you contact dno about it if it's happening or is it acceptable Because I got friend to clamp main earth on a 3 phase large commercial unit today and he was getting similar reading to the house I'm working on.

Sorry for all questions..

 

[Lucien Nunes]

The current you are measuring in the earthing conductor is not leakage, it's a fraction of the normal neutral current from any and all installations finding its way through parallel paths connected to the PEN. It's not a problem and it can't be eliminated.

 

[plugsandsparks]

Very common, see post 9

 

[Edward67]

Very common, see post 9

Thanks again. Look forward to clamping the offending tails again.

 

[Edward67]

Thankyou plugsandsparks. I went round today. Clamped my tails and got 5mA.
So lesson learned.