Issues with erroneous testing

[pirate]

A rouge neutral might easily be confused with a line conductor, surely...?
Sorry, just a silly Boxing Day joke!

 

[RMS Electrical]

A rouge neutral might easily be confused with a line conductor, surely...?
Sorry, just a silly Boxing Day joke!

Many a true word is spoken in jest

 

[Pretty Mouth]

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.

 

[nicebutdim]

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.

 

[RMS Electrical]

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