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Thursday, 6 March 2014

Finding a Neutral to Earth fault.


In my previous post I wrote about what a neutral earth fault was and touched on some methods to diagnose the fault without having to use specialist test equipment. In this post I would like to describe some first and second hand experiences of this condition. I want to described 3 cases that I hope to illustrate how awkward this fault can be to diagnose and locate. It also gives food for thought if you have experienced similar issues.


Please note that this article is my opinion and cannot be considered advice.  For any issues regarding any electrical fault or installation, seek the advice and knowledge of a qualified electrician fully conversant with the laws and regulations of your country or region. Where the applicable regulation specifies a specific installation or action, this must be followed to comply with your regulations.




Contents




Case one: The night light mare.

Case two: An unusual cooking trip.

Case Three: The screwed up mains circuit.





I consider myself to be both respectful and competent around electricity. I have worked in many companies on both power supplies and mains filtering technology. I fully appreciate just how dangerous electricity can be. You should not be any less careful just because you may have fuses or RCD protecting a circuit you are working on. I always take the view that it is still live and potentially lethal and always test first and ensure any appliance is physically disconnected before starting any work. 

"Complacency kills!"

Always check and double check or get someone qualified who is skilled in electrical diagnostics to do the work for you. If you are unsure or slap dash, employ a qualified electrician. Just because it may be switched off, at the socket, does not mean it is disconnected from the mains.  Make sure you see both a physical disconnection and/or test that mains is not present. Even then you’re not out the woods as there could be a charged high power capacitor such as in a microwave, Cathode Ray Tube (CRT), Power Supply Unit (PSU), etc. A charged capacitor could still retain a lethal voltage even hours after disconnection.





Case one:  The night light mare





The first time I ever heard of this type of  mains power problem was when a work colleague was explaining a strange fault that had him puzzled for ages.  It initially appeared to him as an intermittent fault with his distribution panel or consumer unit. The issue only manifested itself while the outside light was switched on and when he had a sufficient electrical load to raise the neutral voltage, allowing the residual current to rise to a level that would trigger the trip.

A number of power hungry appliances running concurrently such as electric heater, washing machine, dishwasher, etc., would allow sufficient current in the neutral conductor, generating a proportional rise in the neutral conductor voltage relative to the earth conductor. The result was the Residual Current Circuit Breaker (RCCB) would appear to be triggered intermittently as it coincided with a perfect storm of combined maximum current flow from the appliances. The lights powered by the faulty circuit were sensor activated security lights, so they were normally left switched on.

This particular part of the faulty circuit had water ingress and consequently allowed sufficient leakage current to flow in the circuit to trip the RCCB. He was not aware that this issue had developed and was not looking for this type of fault. In fact he was not even aware of such a fault scenario even existed. There was no direct short and the security light appeared to work without issue, so he had no reason to suspect it or its wiring causing the intermittent triggering of the RCCB.

It was only by chance that he finally discovered water was getting into the wiring. One day the bulb blew due to its natural lifespan. He noted that when the light was disconnected via the isolation switch the RCCB did not appear to be intermittent.  It was this event that inspired a casual inspection of the cable and fitting which indicated that there was water ingress. Once he had noted what was going on, he managed to isolate the circuit and replace the faulty wiring.

  • The neutral conductor of the faulty circuit would have a lower resistance to ground due to the water, but because the neutral conductor is normally connected to ground at the grounding equipotential bus bar, this fault would not be obvious if you manually measured it in circuit. To be able to manually measure or discover the low resistance would  require the neutral conductor or the circuit under test to be temporarily disconnected from the central grounding bus bar. This was effectively achieved via the isolation switch in this particular case. An alternative would be to perform an insulation flash test by a qualified electrician.

Here is a video I found describing what happens in a modern insulation resistance test or what I know as a flash test.


So it was ultimately luck that finally alerted him to poor cabling and resultant excessive residual leakage. Once rectified the intermittent tripping fault vanished. It was later that he put two and two together and realised what had transpired and it was the water ingress that was responsible for the intermittent fault even though the current draw from a totally different unrelated circuit was causing the actual trip condition.

This fault would have been discovered by an insulation flash test as is common practise today. In that era (mid 90’s) insulation tests such as a flash test were not necessary in the UK, as they are today. Consequently finding an electrician with the correct equipment capable of doing it was difficult and would have been expensive.




Case two:  An unusual cooking trip.



I had a similar issue happen to me when I powered up an underused element in an electric oven. I have a combined gas and electric cooker where the hobs are gas and the ovens are electric. This was a double oven model with 4 heating elements in one oven and a further 3 in the other.

Normally I would use a separate combined microwave, convection oven to cook as well as the gas hob. As far as for the oven, I had only ever used a single element in convection mode to do any cooking. To this day one of the ovens has never been used, in 10 years!

Anyway, one day in a flash of inspiration, I thought I would do something different and try some of the other heating options. The oven worked happily for 30 minutes before tripping the Residual Current Circuit Breaker (RCCB) and consequently all the resulting mains sockets for circuits supplied by that RCCB.

My usual practise during a mains event is to first switch off all circuits supplied by the RCCB via their associated MCBs. This allows the RCCB to be reset without the possibility of arching. I was initially baffled because the RCCB refused to reengage. Fortunately I was aware of the possibility of the neutral to earth fault and (after some head scratching) I was able to quickly isolate the problem by first physically removing all appliances on all circuits supplied by the RCCB and then switching off all permanently wired appliances via their dual pole isolation switches.


Once isolated the RCCB could be relatched and I switched everything back on, in reverse order, until the RCCB tripped again. Following the principle of, “the last thing to change was probably the cause,” I discovered that it was the oven part of the cooker tripping the residual current device. Once I isolated the faulty appliance, I switched everything else back on and specifically confirmed that it was the cause of the fault.

Here is a video I found, describing this process.



  • The isolator switch for the cooker allowed the neutral to be disconnected and so the RCCB could relatch. To confirm that it was definitely the oven, I then switched everything off via the MCBs and disconnected all appliances. Reconnecting the cooker initially worked but as the oven selector dial was selected to activate the various elements the RCCB would trip immediately.

Identifying the origin of the fault within the cooker's oven was much more awkward due the trouble of tripping the main part of the house via the RCCB. First I had to put the cooker on its own circuit as tripping the whole house every time you make a mistake is very annoying and potentially damaging to other electrical appliances (and personal relationships).

Fortunately, when the house was wired, I had a single socket supplied by a single circuit which was individually Residual Current Device (RCD) protected. Something which would be uncommon under the current UK regulations but not impossible! This particular circuit was intended for a freezer and the logic behind it was that, if the main RCCB was tripped, disconnecting the house circuits, then the freezer would remain powered preserving its contents. I still wanted the outlet protected by an RCD so I installed a combined outlet and RCD socket.

To use this socket for the purpose of diagnosis, I had to run an extension from the socket to the cooker and install a 13A plug on the cooker lead. In the UK all plugs are fused meaning that although the cooker was rated at 16A it would not be able to draw more than 13A. This was not a problem as the RCD would trip before it went anywhere near this sort of current draw.

Such a setup would not be possible where a house is using a single RCCB protecting all the consumer unit's circuits,  With the current UK regulations of having a split RCCB based consumer unit would still result in the very irritating tripping of one or other section of the house.  The only option would be to use an isolation transformer such as a variac to ensure that the appliance is isolated from the RCCB and any faulty residual current will not be able to trigger the RCCB.

  • An isolation transformer used for diagnostics is really something that should be used by a competent professional as there is a serious danger of electrocution. It is especially important to understand how it is earthed and if it is connected to the common equipotential bonding.

In my case, the make of oven worked by using the built in thermocouple to switch live and a selector switch to connect the neutral for the various heater elements.   7 heater elements on my particular oven.  The only way to work out which element was causing the fault was to physically disconnect the individual neutrals from all the elements and add each in turn until I identified the correct faulty element.  The first time it took me a day to find the issue as I was unsure what I was doing and so needed to be both cautious and meticulous.  The second time it only took an hour.

  • The jumble of wires inside the oven was something else.  Modern technology such as the camera phone in your pocket, or tried and tested methods of using pen and paper are essential.  Never assume you will remember!

  • Heating elements are a common cause for earth leakage events.  I have only ever had two earth leakage events and both were heater elements causing a neutral to earth fault. In both cases the element would have worked if powered normally but the leakage fault is usually an indication that it is soon to fail. The heating element construction is usually resistance wire covered in a metal jacket.  The live and neutral attach to the ends of the resistance wire and the jacket is usually earthed using the appliance socket supplied earth.



Case Three: The screwed up mains circuit.



Interestingly, I described my adventures to a friend and how perplexing it can be if you are not sure what was going on.

He had bought a house which was maintained poorly by a DIY enthusiast who cared little for either conventions or safety. The wiring was a maze of extensions off spurs off the main ring main. From the sections I saw the only reason the house hadn't caught fire was because of the general trend for lower powered appliances.

  • The British concept of the ring main is unusual in that typically a 26A cable is used in a ring configuration and protected by a 32A fuse. In a Ring configuration, each socked is supplied from either side of the ring circuit. Optimally all sockets would be on any one ring main and each ring main is protected by a dedicated fuse or Miniature Circuit Breaker (MCB) in the consumer unit. Only a single level of spur (extension) is allowed to any single double socket which cannot be part of the ring circuit. This is because the double socket is rated at 26A and the limitation is governed by the fuses in the standard British plug with a maximum value of 13A per plug.  Essentially this is the only scenario where a fuse is used to protect the mains wiring, "upstream" from where the fuse is installed.  Fuses tend to protect what is downstream from the fuse.

    • The British concept of the ring main was born in the 40's during the major rebuilding process after the 2nd world war. It was conceived from a necessity to preserve copper. Copper wire needed to be used effectively while still allowing an, "unlimited," amount of sockets to be fitted within the home. The higher rated circuit resulted in a higher powered circuit overload fuse, protecting the ring main. This in turn necessitated another smaller safety fuse to protect the wire from the socket to the appliance. This additional fuse avoids the dangerous scenario that a 3A rated flex cord would need to pull 32A before the main circuit fuse blew.  This is why the British square pin plug is fused but it also allows the most appropriate fuse to be used for the cable flex supplying the appliance. This is an advantage not possible in the more common radial circuits used in the most of the rest of the world.

  • That whole discussion about, "what do fuses protect," is really for another post.

So as the house was renovated, sections of the house were returned to complying with the current wiring regulations and normal wiring conventions. Having completed most of the house renovations he needed to have both the kitchen and bathroom rewired.  This required the services of a certified professional able to supply a certificate of conformity.  The certificate required that all circuits be tested under the current UK regulations. He took the opportunity to have the consumer unit replaced, from the original non conforming unit, to a more modern split load, dual Residual Current Circuit Breaker (RCCB) protected consumer unit.

During the conversion it was discovered that one section of his circuits refused to allow the RCCB to latch.  This initially confused the electrician who assumed that he had made a mistake and started to undo his work assuming he had caused the fault. Realising they had a neutral earth fault, they then needed to try to locate where it was. They isolated the neutrals and quickly found the circuit causing the fault. The faulty circuit was identified as the only part of the house's wiring that had not been tackled, as yet, during the renovation. My friend being familiar with testing for shorts was able to narrow the field of search to within the wiring connecting two sockets by using a low ohm meter. The wiring was then tracked and mapped and the specific fault was identified by a combination of vision and deduction. ie. when they looked at the path of the circuit they worked out the most likely causes which could cause the neutral and earth to be shorted.

It turned out that the original DIY enthusiast fitted a cabinet and managed to drive a screw into the mains cable between the neutral and earth wires severing the earth for part of the circuit and connecting the neutral to the earth for the remainder.  The sockets had been used without issue for a year without any knowledge that there was a fault. Possibly many years by the previous owner.  Even a simple mains tester plug did not discover or indicate this fault.

It was only when the RCCB was to be fitted that the problem had come to light. Had it been on an unprotected circuit this issue would never have been found.

Mind, if the electrician did this test, as in the video below, he wouldn't have connected the faulty circuit as he would have known that the earth wire was broken.







Further reading and references for this article:   take a look at the resource page:



Please note that this article is my opinion and cannot be considered advice.  For any issues regarding any electrical fault or installation, seek the advice and knowledge of a qualified electrician fully conversant with the laws and regulations of your country or region. Where the applicable regulation specifies a specific installation or action, this must be followed to comply with your regulations.





18 comments:

  1. Please I have a problem with my light, the neutral brings out light sometimes it cause high voltage to the house I don't know what to do to elinate this neutral leakage. But I want answer to this question, please can I use earth as neutral pending the time the neutral will be corrected?

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    Replies
    1. Hi Tessy, the direct and simple answer to your question is "NO," do not use the earth wire as an interim fix for a bad neutral, even as a very short-term fix. This is a very bad idea. Assuming it is indoors, the correct workaround is to use a different light source, even a table lamp with an extension cord, until you get a qualified electrician to sort your problem out properly. My personal experiences of short-term measures are that they rarely end up being short term. The old saying that "tomorrow never comes," sounds so familiar in these situations.

      The explanation of the reasoning for the answer is fairly extensive and is worthy of a couple of posts alone, possibly even three! This particular post you have attached your question to is really about an awkward fault of a neutral to earth fault which most people haven't even heard of. The fault you have sounds like a floating or intermittent neutral, which is a very different type of fault. While a neutral earth fault can be a terrible nuisance a floating neutral can be anything from inconvenient to seriously life threatening. It very much depends where it is. If it is within a well-designed appliance it will be inconvenient. If it is in the distribution network side and you have a TN-CS derived earth and you're in the UK, then there is a worst case potential that your neutral and earth could wander sufficiently that you have 415Vrms between live and neutral and your equipotential zone could be floating at 240Vrms above the surrounding neighbouring Earths.

      A floating neutral on the distribution side can be considered a distribution network emergency, as it may be more than just you affected and you're in a very real and present danger of electrocution. It is the responsibility of the network suppliers to fix this type of distribution fault. A floating neutral can be an odd fault as at times everything appears to work perfectly and then it can appear that your supply is possessed by some sort of poltergeist. Appliances with switch mode supplies can be very tolerant of minor voltage changes and bad supplied voltage but old tungsten filament lighting may expose such a problem as flickering and randomly changing light levels especially in the evening and at night. Not to be confused with switching which is due to deliberate and careful changes to the power distribution network as power stations go on and off line.

      To a UK based electrician the earth wires proper name is the Circuit Protective Conductor (CPC). I use the colloquial expression of "earth" just for simplicity. The probable reason it is called a "CPC" is because calling it "earth" gives a misleading idea of what the circuit is there to do, which is protect you. (see the post http://www.cycloflow.com/2014/02/the-pain-of-neutral-to-earth-fault.html especially the part about equipotential zones).

      To bypass this safety feature, even temporarily, would be irresponsible especially if the next person to deal with "the fix" isn't properly aware of what has been done. The CPC is designed specifically to take quite high short-term fault currents or very low-level static voltage correcting currents. It would not be suitable for taking general working currents as it would be underrated for the protective fuse or MCB in the distribution panel or consumer unit (see the post http://www.cycloflow.com/2014/03/what-do-fuses-protect.html). The UK earth wire in domestic solid core mains cabling is undersized compared to its neighbouring live and neutral conductors and so would present a higher resistance to current when compared to these conductors. The other way to look at it is that the earth wire is exactly the correct size for its intended purpose.

      Suggesting you use the earth wire as a temporary fix would be like sanctioning you to hang the Sword of Damocles above your head! Not only would you be using the wrong sized conductor but you would no longer have the protection of the CPC for this part of the circuit.

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  2. This comment has been removed by the author.

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  3. I have an intermittent RCCB trip at home which happens once every few days. The RCCB can be reset only if one of the MCB (No. 6) is turned off. The next day, I will be able to reset MCB No. 6 without tripping up the RCCB.

    An electrician has taken a look at the sockets affected by MCB 6, but found no issues with the sockets. As a test, the Earth wire for the circuit controlled by MCB 6 was disconnected at the distribution box for further monitoring.

    Now, even with the Earth wire (at distribution box) for circuit of MCB 6 disconnected, the RCCB trip will still occur intermittently. What kind of fault do you think it is, and what solution or testing can be done to solve it?

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    Replies
    1. Hi Steve,

      Please note this is my opinion and does not constitute advice. You didn't say if the electrician confirmed that the RCCB was working correctly and was tripping at its correct leakage current, such as 30ma. Intermittent faults are the bane of technicians the world over, as they can be very tedious to diagnose. The best weapon for intermittent fault diagnosis is diligent documentation of what you did, what has been done and the events around each fault occurrence. I have lost count of how many times I have heard sentences, which start with the words, "I think..."

      Intermittent faults are normally caused by a borderline fault and some sort of trigger event which tips the balance. If you can identify the trigger event you can control the fault, to help aid in the diagnostic process. A bad diagnosis is when you believe that the trigger event is the problem and thus ignore the underlying borderline problem, which invariably resurfaces sometime later. A trigger event could be electrical/RF noise, over/under voltage, physical/mechanical/electrical issue due to thermal expansion or contraction, mechanical movement etc. So I would keep an open mind and try as best I can to take copious notes, to see if I can find any more obvious correlations.

      My understanding from what you have written is that, when the RCCB has a trip event, only the circuit/MCB in position 6 needs to be left open to allow the RCCB to reset. The MCB in position 6 can then be switched back into circuit sometime afterwards without immediately tripping the RCCB. If my understanding is correct, then it would suggest that the fault is partially persistent for a small window before it seems to clears sufficiently to allow a successful reset of the MCB. If so it gives a good window for diagnosis of the fault.

      This is how I would approach the problem with pen and paper in hand.

      Please note that if you have disconnected the circuit earth wire (CPC) for monitoring purposes, you need to confirm that it has "actually" been disconnected from earth. There is every possibility that it might have another path to earth via an equipotential bonding path or through cross connection via appliances such as telecoms cabling, hifi cabling or pipework/chassis connections, etc. Confirm this with a resistance check and voltage checks. Ensure that you have marked your installation in such a way that you don't accidentally forget to reconnect it.

      Possible Causes of fault to try to isolate

      1) Bad RCCB.

      2) Normal sum of the accumulated leakage on all connected appliances means the RCCB is borderline.

      3) Bad appliance or appliances.

      4) Bad supply circuit:

      4.1) Live conductor is leaking to:

      4.1.1) Another live conductor but not on the same RCCB.
      4.1.2) Another Neutral but not on the same RCCB.
      4.1.3) Either the Circuit protective conductor (earth wire) or another Earth.

      4.2) Neutral is leaking to:

      4.2.1) Another live conductor but not on the same RCCB.
      4.2.2) Another Neutral but not on the same RCCB.
      4.2.3) Either the Circuit protective conductor (earth wire) or another Earth.

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    2. Part two of reply

      Preliminary testing, best done by electrician with suitable equipment.

      1) First is to map "everything" on circuit "position 6" and where it goes throughout the dwelling. Pay attention to damp walls, external routing or unventilated and damp areas.

      2) Confirm using a leakage "ramp test" that the RCCB has the full 30ma leakage (within specification) available when all circuits and appliances are disconnected.

      3) Add circuits individually, one circuit at a time and re-run the leakage ramp test each time to confirm how much leakage is on each circuit. If any circuit seams particularly leaky, perform the same test but on an appliance level for that circuit to identify the biggest offenders. Electrical noise suppression filters such as in power supplies can be leaky, especially when metal oxide varistors are getting to the end of their life.

      4) If circuit 6 is particularly leaky, confirm and qualify if it is the fixed installed wiring or the various appliances which are causing the majority of the leak, as per point (3). You may just have an accumulation of leaky appliances leaving your RCCB little room for manoeuvre, thus requiring you to consider sharing the leakage load with further RCCBs or RCBOs.

      5) Check the voltage and, if possible, the quality of the supply while everything appears to be be working.

      6) Perform an insulation flash test on circuit 6 to confirm the integrity of the circuit's insulation. Using a standard multimeter is "not" the same thing!

      7) If possible it would be advisable to have an insulation flash test and on all the other circuits.


      Diagnostic process

      8) When the fault occurs confirm it is persistent and you are unable to reset the RCCB, then check the supply voltage and if possible, the level of the mains born noise. A much higher supply voltage may indicate a distribution fault and the resulting higher leakage in your dwelling is triggering the intermittent trip. This scenario is more likely if the accumulated leakage from all the appliances does not leave much in the way of "head room" for the RCCB to hold integrity.

      9) Confirm that when in a fault state that if you power off all other circuits, via their MCBs, you can reset the RCCB and only MCB 6. If you can successfully re-latch MCB 6, start re-latching the other circuits to see if there is another circuit combined with MCB6 which causes the RCCB to trip. If it is only MCB 6, and the RCCB cannot be latched when all other circuits are powered down, it would strongly suggest that the problem is predominantly a leakage from the live conductor of circuit 6 or from the live side of an appliance attached to circuit 6.

      10) If it's possible to temporarily remove all appliances from the circuit in position 6 for at least one fault event. This will help to confirm that they are not the main culprits. Consider if they can be temporarily moved to different circuits to check if the fault follows any of the appliances.

      11) If you find a potentially rogue appliance test it individually, in case you have a neutral earth fault somewhere else in the installation. Hopefully the insulation flash test as in point 7 would indicate that the distribution wiring is sound.,

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    3. Thank you very much for the super detailed reply! I have engaged a professional electrician with the appropriate equipment to conduct some tests, and he will be coming over in a few days. Hopefully the testing will turn up some results and we can nail down the root cause. Your opinion is very much appreciated.

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    4. The electrician came around today and we spent 2 hours troubleshooting the wires and sockets on circuit 6. During the Megger test, we found that on one of the two live wires at the distribution box (2 wires since it is a ring circuit), the resistance was low.

      It was >100 M-Ohm on one of the live wires, but only 0.1 M-Ohm on the other live wire. There were 8 sockets on circuit 6 and we dismantled the sockets to find out which socket is connected to the defective live wire.

      Finally we traced the defective live wire and taped it off. Circuit 6 is now not a ring circuit but more like a serial layout. As you suspected, there was current leakage from the live wire on circuit 6 that caused the RCCB to have intermittent trips.

      Hopefully this solves the issue once and for all. Repairing the defective live wire on circuit 6 is quite impossible as the wiring is all concealed and I have no idea where it runs through the house (under floor, through wall, through ceiling?)

      All the sockets on circuit 6 are still functioning even though there is only 1 instead of 2 live wires running to each socket.

      Do you agree with this diagnosis, and do you foresee any further issues? Anything I should watch out for?

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    5. Thank you for your update. From your reply it would suggest you have either isolated a single segment of cable between two sockets or the first leg of the circuit from the fusebox (consumer unit) to the first socket in the ring. I expect that you narrowed this down by segmenting the circuit and by a process of elimination found the faulty leg. I hope you took the opportunity to map the order of the sockets and which is connected to what during this process, since it is invaluable information for future diagnostics and planning. The fault you describe certainly sounds like a good candidate but unfortunately I would consider this an incomplete diagnosis until you have confirmed that the intermittent fault has stopped and you have identified the whereabouts and cause of the low resistance. Your temporary fix, which is to isolate the rogue section and consequently convert your existing circuit from a ring to a radial, would fall into the category of a "workaround." It is up to you to decide whether you find this satisfactory.

      Please note that if you have converted a ring circuit to a radial you will have effectively derated its current carrying capability. The MCB in the consumer unit "must" be appropriate for the circuit and if that requires a lower rated MCB, this must be installed as per your wiring regulations.

      From a personal point of view I would try the following, but please note this does not constitute advice.

      Quick areas worth a careful look are the portions of wire that have been stripped back. See if there are any obvious nicks in the insulation caused by pulling through the cable into the pattress or clumsy installation. If there is too much wire in a metallised socket box, this excess wire can get sandwiched and crushed when the socket face place is attached and fixed into place. Look carefully where the outer insulation has been removed as sometimes a clumsy installer may have partially sliced the inner insulation at that point without realising.

      If you know the general location of the cable, you can take a good educated guess of its route. If you have a nail/stud/cable detector, this might be able to assist you to trace its path more accurately within the walls or even under the floor. The rogue circuit will need to be powered during the mapping process and other circuits would be powered down from the fusebox/consumer unit. Simply switch other circuits off at the MCB. Careful consideration to your, and others, safety must be considered during this process. If you are unsure get the qualified electrician back. This assumes that the detector is designed to detect live wires and not just metal.

      Once you know the general route check for potential offenders such as fitted furniture and decorative items where you might have nails or screws in the wall, floor or ceiling.

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    6. Yes one of the segments have been isolated and it is now a radial circuit. I understand that it is not a solution but a workaround. I will now monitor the circuit and see if the problem goes away, and might change the fuse later on.
      The circuit 6 is in the two bedrooms, and are usually not used much except for the TV and charging devices, and so do not experience high loads.
      The cable load is unknown as the wiring is all concealed and there are no wiring plans (unless I ask the relevant agency for it).

      Once again, thank you for the useful info as I have learnt quite a bit from this.

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    7. Another question: Any idea what might have caused this live wire to cause RCCB tripping, even though it has been working fine for the past 1.5 years? What could have caused it to tip over from "working fine" to "not working some of the time"?

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    8. I'm glad you've made progress but I am concerned you may have changed your home wiring from an annoying but safe installation to a less annoying but potentially dangerous one. Sadly, I would not consider this to be a good outcome if it remains that way. It is all too easy to fall into the trap of "tomorrow never comes."

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    9. The thing is, I don't see how it can be fixed completely, unless I tear up the wall and floor to fix the defective wire.
      Before the workaround, the intermittent trips were not just annoying, but it cut the power to the whole house, including the fridge.
      In your opinion, what can I do to improve the safety of the current workaround set up? Thank you.

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    10. If you plan to make the workaround more permanent, then make sure the workaround is safe, you need to ensure that the MCB rating is appropriate for your wiring with a change from ring to radial. For example of my own wiring, I use 26A rated cable in a ring and that's protected by a 32A MCB. I believe The UK regulation say it must be less than 3/4 the theoretical full current capability of 52A (I cannot find the exact wording at this moment). If I was to change this to radial, the new rating of the MCB would need to be less than 26A. In my case that would mean I would need to install a 20A MCB as the next preferred value available for my installation. Leaving a 32A MCB in place would be considered dangerous.

      This could be entirely different in your regulations, but I urge you to make sure your wiring complies with your regulations.

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    11. The current MCB for circuit 6 is 32A. As I am in Singapore, which generally follows UK standards, your numbers should apply too. There are a few spare 20A MCB in the distribution box, so it is just a matter of switching over.

      Do you suggest swapping the MCB of circuit 6 (change 32A with the spare 20A), or just moving the live wire from the circuit 6 MCB to the spare 20A MCB?

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    12. Both options have their merits, and the final choice will be based on many factor such as conductor lengths, including the neutral and earth wire/(CPC) as their position should reflect where the live conductor is connected. The labelling of circuit on the front panel, the ease of access to the DIN rail release, assuming you are using DIN mounted MCBs. For some it will be the installation wiring Feng Shui, which more seasoned electricians pride themselves on. All of these considerations I cannot see, so it would be entirely inappropriate for me to provide or even suggest remote advice. Such a change is really a "bread and butter job" for any qualified electrician and I cannot see it taking more than 30 mins, all in.

      For my own personal installation, I would have no choice but to replace the MCB. Due to the irrational design of the DIN rail release location, I would have to disassemble the live bus bar before a swap of the MCB and reassembly. Such a lot of work would offer many possibilities for miss-connection but any good professional is unlikely to make such an amateur mistake. I will bat this question back to you and ask you to seek local professional advice.

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