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Hi folks. Im a RECI contractor based in Co Sligo, Ireland . I was doing erroneous testing on a domestic board which gave me readings between 90V- 190V-240V on each of all 6 Live circuits of the RCD group.

Whilst testing for erroneous circuits, I had isolated the mcb I was testing and energised the other 5 circuits. The readings are as stated above.

Previously, in addition to the erroneous testing, I also carried out Insulation Resistance tests (Meg-Ohm) of all live conductors to each other, ie 1-2, 1-3, 1-4 etc, about 11 tests as two circuits were ring-main circuits . All readings were above 500Megs.
Similar tests were performed on each of the (disconnected) neutrals, all above 500Megs. I then repeated erroneous testing but instead of looking for a voltage at the mcb, I used the 3-pin plug lead on my Fluke 1653, and did a voltage test at each socket-outlet of the circuit under test = No Voltage shown.
This was performed on all RCD circuits.

I suspect a spur N, or L & N with a load is hiding within the installation. I noticed these erroneous voltages showed up whilst testing the additional work I had carried out, and duly had to submit a Number 3 Certificate.
This scenario is wrecking my head even though I qualified as a spark in 1975.
Any suggestions are welcome.
Robert Mulgrew
 
TL;DR
I need some help with erroneous test results: false voltages showing up
Hi. Also a RECI contractor. So to clarify you're doing the erroneous connections test the second (new) way rather than the traditional insulation test between phase conductors?
 
Hi. Also a RECI contractor. So to clarify you're doing the erroneous connections test the second (new) way rather than the traditional insulation test between phase conductors?
Hi Risteard (is that your name or title?) The IS10101 lists two ways of testing for erroneous circuits: The first is pre-connection (insulation resistance) between the current carrying conductors , the second is a post connection (voltage) test across an mcb that has been switched off, with all other mcb's energised .
I discussed this topic with Dave Butler, and he said that I can use any test or means to establish the absence of erroneous circuits. So I posted that I tested for the erroneous voltage at the sockets using my plug lead with a Fluke multitester. I discussed this in my post.
By the way "the second test" as you called it, has been around for 7 years or more.
Did you actually read my whole post?
Can you even try to explain how or why I got the readings I mentioned? What am I missing here?
I asked for (new) advice or suggestions, not just what the book states.
RMS
 
Hi Risteard (is that your name or title?) The IS10101 lists two ways of testing for erroneous circuits: The first is pre-connection (insulation resistance) between the current carrying conductors , the second is a post connection (voltage) test across an mcb that has been switched off, with all other mcb's energised .
I discussed this topic with Dave Butler, and he said that I can use any test or means to establish the absence of erroneous circuits. So I posted that I tested for the erroneous voltage at the sockets using my plug lead with a Fluke multitester. I discussed this in my post.
By the way "the second test" as you called it, has been around for 7 years or more.
Did you actually read my whole post?
Can you even try to explain how or why I got the readings I mentioned? What am I missing here?
I asked for (new) advice or suggestions, not just what the book states.
RMS
I'm aware that the voltage test is permitted. I referred to it as the "new" way because it is referred to in I.S. 10101, but wasn't in ET 101. I was just trying to clarify how you have done the erroneous connections test first before getting into what you are finding when carrying out the test. I certainly wasn't trying to offend you, so I'm not sure why you appear to have interpreted my question that way.

You will find videos which RECI produced around the time I.S. 10101:2020 was released which had Seamus Greene, Dave Butler and John Cotter, which included the Post-Connection method (for want of a better name for it).
 
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I'm aware that the voltage test is permitted. I referred to it as the "new" way because it is referred to in I.S. 10101, but wasn't in ET 101. I was just trying to clarify how you have done the erroneous connections test first before getting into what you are finding when carrying out the test. I certainly wasn't trying to offend you, so I'm not sure why you appear to have interpreted my question that way.

You will find videos which RECI produced around the time I.S. 10101:2020 was released which had Seamus Greene, Dave Butler and John Cotter, which included the Post-Connection method (for want of a better name for it).
Hi Risteard, happy boxing day.
Not offended, we just used different terminology for the same thing.
I saw that video with the three dudes, they used a cable drum as a table if I recall...
Never mind the procedures and which standard was used, if you can't answer my main question, just say so or leave the thread. I wanted advice and/or a technical explanation of why you thought I was getting those high voltage readings at the (open) mcb, but at the same time, no voltage shows up when testing the socket?
Please try to give me a logical explanation.
Thank you
 
Having the procedures and by the book testing explained first helps us that aren’t in the same country to understand and maybe think of something else without repeating what’s already been suggested.

I too would like clarification. In simplest terms….
Voltage at an mcb which is turned off, suggesting a cross connection with another energised circuit…. But no voltage further down the circuit ie at the socket outlet.

Have you checked the tester when you did the socket? Ie checked it works on a known good voltage or proving unit, before and after testing the point in question?

Did you break down the circuit in any way to find which length of cable showed the fault and which didn’t?


What is a “number 3 certificate”? Same as UK unsatisfactory EICR?
 
Having the procedures and by the book testing explained first helps us that aren’t in the same country to understand and maybe think of something else without repeating what’s already been suggested.

I too would like clarification. In simplest terms….
Voltage at an mcb which is turned off, suggesting a cross connection with another energised circuit…. But no voltage further down the circuit ie at the socket outlet.

Have you checked the tester when you did the socket? Ie checked it works on a known good voltage or proving unit, before and after testing the point in question?

Did you break down the circuit in any way to find which length of cable showed the fault and which didn’t?


What is a “number 3 certificate”? Same as UK unsatisfactory EICR?
A Cert No. 3 is a Completion Certificate for Existing Installations, i.e. where DSO involvement is not required.

I will not answer the OP's question (which I feel I could have given an explanation for upon clarification as to how the testing had been carried out) due to his attitude in the posts.
 
On holiday in Ireland so will give it a go.... I think from what has been discussed is that a single phase board is installed with a number of ccts and the OP is seeing voltages at the outgoing MCB connection when switched off. The outgoing cable is still connected to the MCB BUT when the OP measures voltage at the far end of said cable it is reading 0V.
This is not a test i am familiar with but to progress i would disconnected the outgoing cable at the MCB and then re-measure to see if its coming from the MCB or cable. Then if it is still there at the MCB i would connect a simple load like a light directly to the MCB or cable and see if the voltage is real or induced. Chances are when a real load is connected the voltage would collapse.
 
Having the procedures and by the book testing explained first helps us that aren’t in the same country to understand and maybe think of something else without repeating what’s already been suggested.

I too would like clarification. In simplest terms….
Voltage at an mcb which is turned off, suggesting a cross connection with another energised circuit…. But no voltage further down the circuit ie at the socket outlet.

Have you checked the tester when you did the socket? Ie checked it works on a known good voltage or proving unit, before and after testing the point in question?

Did you break down the circuit in any way to find which length of cable showed the fault and which didn’t?


What is a “number 3 certificate”? Same as UK unsatisfactory EICR?
Hi there.
In ROI or Southern Ireland as some say, we have 3 types of certificates.


The Certificate Number 3, is issued for alterations /additions to existing installations without DSO involvement (District System Operator) including specific controlled works No 2, 3, & 4, or minor works if requested by customer.

I did check the meter on known /expected voltage readings at the time. Also the false voltage readings were observed at each individual open mcb of the RCD group, ranging from 92Vac - 240Vac, while all the other mcb's were energised.

So it's a case of "thinking caps on", or one for the scientists /engineers.

Thank you for taking the time to explain
Robert
 
On holiday in Ireland so will give it a go.... I think from what has been discussed is that a single phase board is installed with a number of ccts and the OP is seeing voltages at the outgoing MCB connection when switched off. The outgoing cable is still connected to the MCB BUT when the OP measures voltage at the far end of said cable it is reading 0V.
This is not a test i am familiar with but to progress i would disconnected the outgoing cable at the MCB and then re-measure to see if its coming from the MCB or cable. Then if it is still there at the MCB i would connect a simple load like a light directly to the MCB or cable and see if the voltage is real or induced. Chances are when a real load is connected the voltage would collapse.
Thank you plugs n sparks.
Good ideas /suggestions.
I suspect a rouge neutral or complete loaded spur may be buried in the wall, or undiscovered.
I only added 2 circuits with a total of 6 double socket outlets to the existing installation.
Still searching for a answers
Thanx
 
Hi Tim, thanks for input.
I'm a RECI and still in the dark over this issue. Erroneous testing is a post connection test without any connected load. That's why I think there is a hidden load or spurred neutral causing a backfeed. The confusing thing is: I've done the erroneous test across each of the mcb's in the RCD group, * and had a voltage at every circuit, ranging from 90Vac to 238Vac. All loads were disconnected.
* You de-energise the mcb or circuit being tested, while all other circuits on same busbar are energized. The (voltage) test is performed between the busbar and to the load side of the isolated mcb, to test for crossfeeds/erroneous circuits.*

Please help me guys. Even a first-year appie might be able to throw us some clues. It's wrecking my head.
Robert

The post I've quoted is from another thread, but I've posted my reply here, as I think the mods want to keep the topic all in one place.

From what you have described:

You are testing potential difference between 2 points: the live busbar (at 230V potential), and the line conductor of a circuit that has been isolated at the MCB (at unknown potential). This circuit MCB is installed on the same busbar.

If the isolated circuit L was at 230V (ie. it was live), then you would get a reading of 0V or thereabouts. There is no potential difference between it and the busbar.

If the circuit L was at 0V (ie. it was not live, but connected in someway to N or E, perhaps through installed equipment (you don't mention having disconnected N of the isolated circuit), or a tenuous fault to earth), then you would get a reading of ~230V.

If the circuit L had no potential (ie. it is 'floating', has no connection whatsoever to the live circuits, not even a tenuous one), then you can get a range of results: sometimes the voltage tester will give no result at all, othertimes a vague result somewhere in the range 0V to 230V, typically right in the middle of the range.

It sounds like you are getting a mix of the second and third possibilities : it appears that the isolated circuit L conductor is not energised. With either of these possibilities, there is no reason to think that a voltage test between the circuit conductors at any of the circuit outlets would return a potential difference, unless either the N or E was at a raised potential.

I'm not an Irish spark, so am not fully familiar with the test requirements, so I can't say if you are carrying it out correctly or not. However if I was tasked with devising a test to check for interconnections between circuits, it's not what I would have come up with.
 
Hi. Also a RECI contractor. So to clarify you're doing the erroneous connections test the second (new) way rather than the traditional insulation test between phase conductors?

Hi Risteard (is that your name or title?) The IS10101 lists two ways of testing for erroneous circuits: The first is pre-connection (insulation resistance) between the current carrying conductors , the second is a post connection (voltage) test across an mcb that has been switched off, with all other mcb's energised .
I discussed this topic with Dave Butler, and he said that I can use any test or means to establish the absence of erroneous circuits. So I posted that I tested for the erroneous voltage at the sockets using my plug lead with a Fluke multitester. I discussed this in my post.
By the way "the second test" as you called it, has been around for 7 years or more.
Did you actually read my whole post?
Can you even try to explain how or why I got the readings I mentioned? What am I missing here?
I asked for (new) advice or suggestions, not just what the book states.
RMS

Hi Risteard, happy boxing day.
Not offended, we just used different terminology for the same thing.
I saw that video with the three dudes, they used a cable drum as a table if I recall...
Never mind the procedures and which standard was used, if you can't answer my main question, just say so or leave the thread. I wanted advice and/or a technical explanation of why you thought I was getting those high voltage readings at the (open) mcb, but at the same time, no voltage shows up when testing the socket?
Please try to give me a logical explanation.
Thank you

Perhaps I'm reading post #2 incorrectly, but it seemed as though an experienced and well qualified REC simply asked for clarification of a particular point.

I know this doesn't answer your question, but in your position Risteard is the first person I'd turn to for help. Unfortunately he appears to have taken heed of your advice and left the thread.
 
The post I've quoted is from another thread, but I've posted my reply here, as I think the mods want to keep the topic all in one place.

From what you have described:

You are testing potential difference between 2 points: the live busbar (at 230V potential), and the line conductor of a circuit that has been isolated at the MCB (at unknown potential). This circuit MCB is installed on the same busbar.

If the isolated circuit L was at 230V (ie. it was live), then you would get a reading of 0V or thereabouts. There is no potential difference between it and the busbar.

If the circuit L was at 0V (ie. it was not live, but connected in someway to N or E, perhaps through installed equipment (you don't mention having disconnected N of the isolated circuit), or a tenuous fault to earth), then you would get a reading of ~230V.

If the circuit L had no potential (ie. it is 'floating', has no connection whatsoever to the live circuits, not even a tenuous one), then you can get a range of results: sometimes the voltage tester will give no result at all, othertimes a vague result somewhere in the range 0V to 230V, typically right in the middle of the range.

It sounds like you are getting a mix of the second and third possibilities : it appears that the isolated circuit L conductor is not energised. With either of these possibilities, there is no reason to think that a voltage test between the circuit conductors at any of the circuit outlets would return a potential difference, unless either the N or E was at a raised potential.

I'm not an Irish spark, so am not fully familiar with the test requirements, so I can't say if you are carrying it out correctly or not. However if I was tasked with devising a test to check for interconnections between circuits, it's not what I would have come up with.
Firstly thank you for a comprehensive assessment of the system I'm trying to figure out. I had a similar conclusion but could not define it specifically the way you have.

Re your suggestion that I am getting a mix of the second and third possibilities :
A voltage test at the sockets connected to the circuit confirmed your suggestion, ie, that the 0V or no voltage at the sockets proved that the load side of the isolated mcb was indicating a floating pd.

As Risteard pointed out, the "Post-Connection" voltage test meathod for erroneous testing was only recently introduced here in Ireland.

The traditional way is to do a "Pre-Connection" Insulation Resistance test between the L conductors.
When I performed this test the circuits all came up as >500Meg.

Conclusion: I will repeat the new erroneous voltage test, but with the Neutral disconnected.

Thank you for the electrical theory refresher

Robert
 

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