Investigating a faulty earthing in our house

  • #1
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We are facing a severe earthing problem. In our house, the potential difference (PD) between neutral and earth is ## 50 - 60 ~\mathrm{VAC},## which should normally be ##< 2~\mathrm{VAC}## if earth is properly connected. I determined this with my multimeter after some appliances were giving electric shocks. And this value is approximately the same in all outlets inside our house.

Now, I am trying to figure out whether the issue is only in our flat, or throughout the building.

Here is a diagram of the main circuit board in our building:

Home_mains_ckt2_bb.png

There are three lines (phases?) (red, blue, yellow) and a neutral (black) that enter the building. I have not shown the electricity meters, as they're not required. Also, the neutral wires from each fuse (F1-6) are actually separate wires that meet at the company fuse (point D) for the neutral line (similar to the earth wires, which meet only at E).

I measured some potential differences, and the list is as below:

Multimeter probe 1 location​
Multimeter probe 2 location​
Potential Difference (in ##\mathrm{VAC}##)​
Company fuse for neutral, point DEarth, point E
##\approx 0.5 - 1.1##​
Neutral at F1Earth, point E
##\approx 0.5 - 1.7##​
Live at F1Earth, point E
##\approx 229##​
Live at F1Neutral at F1
##\approx 230##​

Our fuse box (F1) is made of metal, so the earthing wire that comes down from our flat is first connected to that metal box, and thereafter connected to point E. I also checked the PD b/w this box and point E, and it was ##\approx 1.5 - 2~\mathrm{VAC}.## It shows that earthing is fine at the main board, so something is wrong in the wires between our house and the main board. We shall be calling an electrician to rectify it.

But I discovered something more. There is a three-pin socket from the common place line near the entrance of our building (it is indoors). I checked the PDs at this location, and found this:

Multimeter probe 1 location​
Multimeter probe 2 location​
Potential Difference (in ##\mathrm{VAC}##)​
LiveNeutral
##230.1##​
LiveEarth
##40.6## (?)​
NeutralEarth
##7## (?)​

Note that I rechecked these twice. But I didn't verify it by checking with F6, the common place fuse.

I am interested in why the value ##40.6~\mathrm{VAC}## comes up, and whether it is of any significance.
 

Answers and Replies

  • #2
anorlunda
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OMG I feel so bad for you. But it is extremely difficult for those in other countries to help. That is because there are more than 60 different wiring and grounding systems in use around the world. People give advice applicable to their own country but wrong for yours.

On the other hand, we have some extremely clever engineers here. I hope some of them can give you useful advice independent of national practice differences.
 
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  • #3
hutchphd
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What are the physical locations of points D and E (and how far apart)?
 
  • #4
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What are the physical locations of points D and E (and how far apart)?
They are on the lowest row on the wooden board, in line with all the other company fuses, and maybe around 10 cm apart. E is vertically a bit below the line of the company fuses.
 
  • #5
Baluncore
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I am interested in why the value 40.6 VAC comes up, and whether it is of any significance.
I assume you are in India, with international standard 230 V, at 50 Hz. We have a similar system in Australia. In MEN systems, the neutral is earthed throughout the distribution system, but there would be only one link between your neutral and the protective earth on your property. That link would be with your fuses or breakers, between the earth and neutral bar in the back of your distribution box. You do not show that link, which should prevent the 40.6 VAC appearing in your building.

I am surprised there is a fuse in the company's neutral distribution. Maybe it is open circuit.

The one link between earth and neutral makes it possible to use Residual Current Detection or earth leakage breakers on many of your domestic outlets.

A high impedance voltmeter will not give you a meaningful voltage reading in a floating or open circuit system because of the capacitance between conductors.

The first test I would do is to connect a 240V filament lamp between earth and neutral, then measure the voltage again.
1. If the breaker immediately cuts that circuit, then you have a good RCD breaker.
2. If the voltage then falls toward zero, you are missing your local ground to neutral link. Call an electrician to restore that link in your distribution box.
3. If the lamp glows red then wires are crossed in your vicinity, you have a problem that certainly needs an electrician to resolve the safety issue.
 
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  • #6
hutchphd
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E is vertically a bit below the line of the company fuses.
And that is a ground buss well connected to a ground rod? (If that buss floats it seems to me that an internal case fault at your neighbor #3 could be bad for you) Are red yellow and blue 3 phases? I think I am agreeing with @Baluncore .
 
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  • #7
dlgoff
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I agree with @Baluncore when he mentioned:
... you have a problem that certainly needs an electrician to resolve the safety issue.
 
  • #8
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Here are some pictures of the setup:

20221118_193042-2.jpg

The first three are the fuses of the three phases. Then comes the neutral. At the bottom right of the board, you can see the point where all the earth connections from different houses are joined. This is connected to the metal pipe via the thick black wire. The metal pipe houses the three phases and the neutral wires and runs underground. In this way, the company ensures that the earth wires are actually grounded.



The fuse in the neutral line.



Edit: Changed second picture to a better image.
 
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  • #9
Averagesupernova
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I avoid posting in threads like these because I always question the accuracy of the system as it is described. If you have little to no voltage between D and E in the first diagram but are getting shocks from appliances, the problem is like two fold or more. Likely an open earth, but it also implies something is putting voltage on this open earth wire which is common to many appliances. The three pin socket you refer to that you measure 40 volts neutral to earth is likely just another symptom of the same problem.
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My guess is the open earth has existed for quite some time and some appliance or load has developed a fault and is now showing up.
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How to troubleshoot it? If the voltage between the neutral and earth is able to drive a load such as a small incandescent bulb, watch this light while disconnecting various loads in the house. Watch for the light to go out.
 
  • #10
Lnewqban
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Have you checked the quality (conductivity and physical condition) of those connections?
 
  • #11
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I avoid posting in threads like these because I always question the accuracy of the system as it is described.
I am describing what the company had described to me the last time they came for an inspection (many years back, but nothing has changed since then).
If you have little to no voltage between D and E in the first diagram but are getting shocks from appliances, the problem is like two fold or more.
It seems that the earthing wire(s) that go down from our house to the circuit board downstairs are somehow damaged or have got disconnected. As I've said, the PD b/w earth wires from our house with the neutral is very low when measured at the main board, but there's a huge difference when measured in any outlet in the house. This probably means that earthing is fine downstairs, but not upstairs, which, in turn, implies a problem somewhere in the middle.
The three pin socket you refer to that you measure 40 volts neutral to earth is likely just another symptom of the same problem.
Possible, but note that this 3-pin outlet is in our common place, and hence, the earthing wire is different from the one that comes down from our flat (though they are all joined at the location E).
How to troubleshoot it? If the voltage between the neutral and earth is able to drive a load such as a small incandescent bulb, watch this light while disconnecting various loads in the house. Watch for the light to go out.
Tried that with a 0.5 W LED bulb. If I connect the bulb b/w neutral and earth in our house, it glows (but obviously with a far lower luminosity). But I couldn't pinpoint any appliance.
Have you checked the quality (conductivity and physical condition) of those connections?
Visually, they seem to be ok.
 
  • #12
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there would be only one link between your neutral and the protective earth on your property. That link would be with your fuses or breakers, between the earth and neutral bar in the back of your distribution box. You do not show that link, which should prevent the 40.6 VAC appearing in your building.
If you check the pictures I have posted in #8, the neutral and earth are not connected anywhere above the ground; the neutral is a separate wire while the earth is connected to the metal pipe that ascends from under the ground. Now, they should be connected under the ground, but I can't see that. The low voltage b/w the neutral fuse and point E suggests that they are definitely connected; but not above the ground.

Also, we don't have any residual current device installed on any of the lines. Only F4 is an MCB, all others are fuses.
 
  • #13
Lnewqban
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Visually, they seem to be ok.
Marginal conductivity may still exist, and can be measured with the proper tool.

Has the problem manifested itself for long or short time?
What changes could have be made to the circuit by that time?
 
  • #14
Averagesupernova
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You have already at your disposal a good tool. That is the incandescent bulb. You need to try harder to isolate the problem. Also, how much current are you able sink on the earth from the hot? That should give an indication that may point you in the right direction.
 
  • #15
Rive
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That connection to the metal pipe seem dubious, and I was very reserved with that. Try measuring 'earth' to water pipes at various points.
You can also try measuring current on 'earth' lines by an AC clamp meter (so you don't have to break the line anywhere).

I do agree with @Averagesupernova that this is likely some double fault. One is the earth being broken or weak: other is some appliance 'leaking' current to the earth instead of neutral.

In my book this clearly requires an electrician, and I bet he'll sweat buckets while solving it. Likely, he'll need to check all houses and appliances one by one...
 
  • #16
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Has the problem manifested itself for long or short time?
This is something we are still pondering on. We have not been at home for around six months last year, and before that, I don't remember facing the issue. We have been at home since February this year, but detected the issue only a few weeks back when we started using our immersion water heater. It was giving a shock even when it was turned off. Initially, I had thought only that outlet was faulty, but when I measured other outlets, they too turned out to have a faulty earthing. Some outlets had nearly > 60 VAC difference b/w earth and neutral.
What changes could have be made to the circuit by that time?
House #2 (the one sharing the same phase with us) had a lot of repairing work going on for the last two years. They also got their electricity meter upgraded by the company to 63 A so that they could drive another air conditioner. (Our line, too, is 63 A, which we upgraded back in 2020, just before the COVID.) Their electrician may have messed something up, and our earthing got snapped.
That connection to the metal pipe seem dubious, and I was very reserved with that. Try measuring 'earth' to water pipes at various points.
Will check.
I do agree with @Averagesupernova that this is likely some double fault. One is the earth being broken or weak: other is some appliance 'leaking' current to the earth instead of neutral.
Possible, but, as I said in #11, I disconnected all the appliances in our house with three pins, but the bulb didn't go out.
I bet he'll sweat buckets while solving it.
I am afraid so. The first thing to do is to "restore" the earthing in our house so that the PD b/w earth and neutral lowers to acceptable levels. But how he will locate that exact junction box where the problem has occurred, is something out of my imagination.
Also, how much current are you able sink on the earth from the hot? That should give an indication that may point you in the right direction.
How do I find that (without blowing any fuse)?
 
  • #17
Averagesupernova
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How do I find that (without blowing any fuse)?
Connect a load between hot and earth.
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This shouldn't be that difficult. If you are unable to get the voltage to go away by unplugging stuff in your house then you need to go back closer to the source and start disconnecting the hots. I assume you can do this by turning breakers off or removing fuses. If ALL of the power is off to your house and still have voltage then you have a possibility that your earth connection is shared by a neighbor and this connection is compromised. In this case the neighbor may have a faulty appliance.
 
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  • #18
Lnewqban
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This is something we are still pondering on. We have not been at home for around six months last year, and before that, I don't remember facing the issue. We have been at home since February this year, but detected the issue only a few weeks back when we started using our immersion water heater. It was giving a shock even when it was turned off. Initially, I had thought only that outlet was faulty, but when I measured other outlets, they too turned out to have a faulty earthing. Some outlets had nearly > 60 VAC difference b/w earth and neutral.

House #2 (the one sharing the same phase with us) had a lot of repairing work going on for the last two years. They also got their electricity meter upgraded by the company to 63 A so that they could drive another air conditioner. (Our line, too, is 63 A, which we upgraded back in 2020, just before the COVID.) Their electrician may have messed something up, and our earthing got snapped.

It is then possible that some connection through the shared ground rather than neutral has been done next door.
Your house is powered backwards from the other house, making your ground invalid (your body has become a better ground).

For a few minutes, may you fully shut down power supply to house #2 to test that?
 
  • #19
Averagesupernova
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It is not uncommon in the USA to have current on the wire that connects the main buried water pipe when the main breaker to the house is off. I won't confuse the issue with details but I want it to be clear that troubles in a neighbor's house can show up in your own.
 
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  • #20
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If you are unable to get the voltage to go away by unplugging stuff in your house then you need to go back closer to the source and start disconnecting the hots. I assume you can do this by turning breakers off or removing fuses.
This is what I did:

Inside our house, there is an isolator (not sure whether it is SP or DP), and after this, there are separate fuses of low rating for each room (or a set of rooms, sometimes). However, as per the standards, single high current lines (> 8 A) have to be directly drawn from the main circuit board downstairs. So, the wires to the outlet for our air conditioner is directly drawn from F1 and bypasses the isolator. It has a separate 11 A switch-cum-single pole MCB (similar to this, but with lower rating than the one linked). Therefore, switching off the isolator has no action on this outlet; it can only be switched off from F1.

I put the bulb b/w live and neutral neutral and earth in this outlet, and it was glowing with low brightness, as usual. Then, I switched off the isolator. (In this situation, the whole house has no power except that outlet, and no appliance is connected to that outlet, except the bulb.) The bulb flashed bright for a second, and then became dimmer, but still continued to glow. Switching on the isolator increased its brightness to what it was initially.

Let me know what this means.
For a few minutes, may you fully shut down power supply to house #2 to test that?
Don't want to get killed!

Edit: Fixed mistake sighted in #24.
 
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  • #21
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For a few minutes, may you fully shut down power supply to house #2 to test that?
On second thought, I can try to do that in the following days when they are not at home. What exactly are the things I should note down? Only whether the bulb glows b/w neutral and earth (and whether it becomes dimmer or brighter)? Should I also note down multimeter readings? Anything else?
 
  • #22
Lnewqban
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On second thought, I can try to do that in the following days when they are not at home. What exactly are the things I should note down? Only whether the bulb glows b/w neutral and earth (and whether it becomes dimmer or brighter)? Should I also note down multimeter readings? Anything else?
You should not see any problem in your house if next door house is not powered, if our assumptions are correct.
Do you know any good electrician who could check the problem for you?
 
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  • #23
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Do you know any good electrician who could check the problem for you?
Ultimately, I will be calling one, but I wanted to narrow down the problem as much as possible (and learn something in the way, too!).
 
  • #24
Averagesupernova
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I put the bulb b/w live and neutral in this outlet, and it was glowing with low brightness, as usual.
Live and neutral or live and earth?
 
  • #25
Baluncore
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What exactly are the things I should note down? Only whether the bulb glows b/w neutral and earth (and whether it becomes dimmer or brighter)? Should I also note down multimeter readings?
Connect a filament lamp between Earth and Neutral.
Does the lamp glow ?
What is voltage across the lamp, before and after ?

Once you have performed that test, it will be possible to work out the next step in the search for what must be at least two faults.
 
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  • #27
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Updates:

I tested with the neighbour's (House #2) main switch (F2) off. There was no change in the readings in our house.



Following the advice of @Averagesupernova, I tried harder to debug and find if there was an appliance which was faulty, as many others pointed out too. To this effect, I took some more data.

The only 3-pin appliance currently working in our house is the refrigerator.

Here is a schematic of the circuit inside our house which will help understand the data I took.

room_wiring_bb.png

Note that I am unsure whether the isolator is SP or DP. The refrigerator is connected through the isolator.

The data is summarized in the Google Sheet below:



What I can see:
  • When the compressor of the refrigerator is running, the difference between earth and neutral is greater than ##10-12~\mathrm{V}## compared to when it is not running.
  • However, the PD is almost the same when the refrigerator is unplugged vs. when the refrigerator is plugged in and the compressor is not running.
Can we infer that the refrigerator is not at fault here? What other conclusions can be drawn (in addition to the fact that the earthing is faulty, and needs to be rectified by an electrician)?
 
  • #28
hutchphd
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You should not see any problem in your house if next door house is not powered, if our assumptions are correct.
No. You are ignoring the other houses at the other two phases. They can be equally culpable in backdriving, and can , in fact, be worse.
@Wrichik Basu Have you done the tests @Baluncore suggested? My working hypothesis is that the local Earthing network is not well connected to either Earth or Neutral. Then any faulty appliance in any house can create a serious problem for all.
Or spend your effort finding the best electrician you can , show him/her your diagram, and indicate you want an explanation of the problem when it figures out.
 
  • #29
Baluncore
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I am going to ignore this thread until the filament lamp test has been done.
 
  • #30
Averagesupernova
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Yes, please use the incandescent when doing tests.
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Let's get back to the fact the that there is very little voltage between D and E in the first diagram you posted. The assumption is a poor connection in the earth conductor as you get away from what is point E in your diagram. I am going to stand by what I said in my first post about concerns whether the system exists as it is presented in the thread. No offense intended, mistakes happen. You may know that each earth pin is supposed to connect back to earth but do you really know the route? I would be familiar with how things are supposed to be done in the USA but what is the practice where you are at? In the USA the earth conductor is run in the same cable or raceway as the hot and neutral back to the source. If there is a broken earth wire in the raceway only devices downstream from that break will be affected. It's not spaghetti when done correctly. Based on your diagrams, I have to wonder about your system.
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Troubleshooting 101: Find a place in the system where readings are correct and you understand them. Then move away from this point until the reading are incorrect.
 
  • #31
artis
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Well @Wrichik Basu , no offense but the pictures you provided show a rather dirty fuse box and the neutral and earth connections do seem oxidized and rusted outright, that can be a problem or part of it, but to know one would need to measure the contact resistance and visually inspect them thoroughly.
I recall one late friend of mine who was an electrician once said to me:" There are only 3 problems in all of electronics, namely
1) A contact where there should be no contact
2) No contact where one should be
and
3) Searching in the wrong place

Apart from the possible ideas already said here one additional idea came to mind.
If I understood you correctly you have a earth wire in each outlet of the house besides the two wires of neutral and live.
So a 3 pin socket essentially. Now apart from the good suggestion that @Baluncore already said in post #5, my additional idea is this.
Clearly apart from bad ground appliances shouldn't leak current to chassis which is a defect in itself.

You could make a short cable with a wall type receptacle on one side and a wall type plug on the other side. Make it out of 3 wires, where you connect L to L, N to N and earth to earth, attach an ampere meter in series on each of the wires.
Then you can go around your house with all appliances disconnected and connect them to your ampmeter cable one at a time.

If truly one of your appliances is faulty itself then you should see a discrepancy between the amp readings of that appliances live and neutral.

This is the same thing a ground fault circuit interrupter does, it compares the current between live and neutral because if everything is ok those currents should exactly match, if they don't there can be only one reason and that is the device is leaking current to ground.
 
  • #32
Rive
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Erm. I think that by throwing in DIY equipment for investigating a live line voltage electric network in unclear state we are treading on thin ice here.
 
  • #33
Averagesupernova
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Erm. I think that by throwing in DIY equipment for investigating a live line voltage electric network in unclear state we are treading on thin ice here.
I think you might be surprised that the "DIY equipment" AKA the incandescent bulb is a very common tool amongst electricians. Do you have another tool in mind?
 
  • #34
Rive
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I know that and I think I would be able to dig up mine from some boxes in storage: I'm myself also fine with extension cords with patched in current measurement (though I prefer clamps instead) but we are in the open here.
 
  • #35
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I am going to ignore this thread until the filament lamp test has been done.
Connect a filament lamp between Earth and Neutral.
Does the lamp glow ?
What is voltage across the lamp, before and after ?

Once you have performed that test, it will be possible to work out the next step in the search for what must be at least two faults.
The first test I would do is to connect a 240V filament lamp between earth and neutral, then measure the voltage again.
1. If the breaker immediately cuts that circuit, then you have a good RCD breaker.
2. If the voltage then falls toward zero, you are missing your local ground to neutral link. Call an electrician to restore that link in your distribution box.
3. If the lamp glows red then wires are crossed in your vicinity, you have a problem that certainly needs an electrician to resolve the safety issue.
I have a 15 W incandescent bulb. Connected it b/w earth and neutral. It didn't glow. (The 0.5 W LED bulb glows, however.)

PD before connecting lamp: 29.84 V
PD after connecting lamp: 30.12 V.

If you want me to get a bulb of lower rating, I will have to search for it.
 

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