Small electric shock on grounded metallic appliances

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iPa41000
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Small electric shock on grounded metallic appliances

Post by iPa41000 » May 14, 2024, 9:13 am

Small electric shock on grounded metallic appliances

This is not a really new issue but it has got worse.
We get small electric shock touching some grounded metalic appliances, really unpleasant, like with toaster, oven and more ennoying with the shower head (now we have a plastic one :lol: ). Then I got same shock with the ground rod when I was digging to check the connection.
My voltmeter between the rod and the ground give my 85V and my amperemeter clamp 2.54A !
Ground drought seems to have an impact, yesterday was a rainy day, this morning I have 23V but 3.6A
3 houses are connected on the same entry, I tried to shutdown (with their main breaker) one by one to highlight a leakage current, but no change.
Note, from 2 weeks we are connected on an another transformator, maybe it is worse from here, I don’t know !
What do you think of all this? :roll:
I have seen other posts about similar issues but didn’t help.
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Re: Small electric shock on grounded metallic appliances

Post by pf-flyer » May 14, 2024, 9:24 am

I suggest that you get an electrician that knows what he is doing to review your hookup and troubleshoot the problem. Electricity is not forgiving if you mess up.
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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 14, 2024, 10:19 am

Now that this is said (and it should be), what interests me is the theory behind it, and the experience of others with the same problem, how it was resolved.
This kind of problem piques the curiosity of an electronics engineer, that's how it is, while knowing the limits not to cross by oneself.

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Re: Small electric shock on grounded metallic appliances

Post by tamada » May 14, 2024, 10:43 am

The appliances are not being grounded. It's impossible to say where the fault lies without knowing where the nearest N-to-ground tie on the power poles external to the property is, how the CU (breaker panel) is wired (it needs to have N-to-ground tied in the box), if there's any ground wire running to the appliance outlets OR has the local 'electrician' used the very common, lazy Thai practice of doing the N-to-ground ties at or near the power outlets. This appears to serve the same purpose as running a ground wire to each outlet... without having to actually run a ground wire. Horribly dangerous as it 'meters out' correctly but doesn't provide any earth-leakage protections.

About 10 years ago, we had the same issue with the 'add-on' kitchen and laundry on our original build. The electrician was a cowboy and however he tapped into the main house wiring to give power to the new rooms left people either getting 'tingles' or 'belts'. We got an electrician in who rewired that part of the building and recommended that the whole house needs rewiring properly.

Just rewired the drop lights in our master bedroom and after being up in the roof space and seeing the death-trap job he did, the total rewiring will be done once the weather cools off.
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Re: Small electric shock on grounded metallic appliances

Post by Bandung_Dero » May 14, 2024, 11:00 am

OK a few readings from within your consumer box (boxes):-
Voltage
Active - Neutral
Active - Earth Bar
Neutral - Earth Bar (As your drawing indicates these is bonded it should be zero)
Was the step down transformer installed by the PEA? The star point (Neutral) should have been securely bonded to Earth there. How far are from the transformer and roughly how many users connected to the distribution lines?
Unfortunately they do not use the MEN (Multiple Earth Neutral) system here in Thailand where ALL consumer boxes have their Earth (an oxymoron here) & Neutral bonded, this ensures the neutral does not get an induced voltage over a long distance.
And yes it is best to have your Earth stake driven into an area which is constantly moist eg. near a garden tap, A/C drain, sewerage pit etc.
I had the problem some 20 years ago and just helped a friend sort his out last month after he had his house rewired, we had the contractor back for another 2 days to sort out his electricians!!! poor workmanship. Mainly faulty connections in most of the GPOs and ceiling junction boxes as well as poor bonding at the Earth Stake. All OK now.
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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 14, 2024, 3:19 pm

Bandung_Dero wrote:
May 14, 2024, 11:00 am
OK a few readings from within your consumer box (boxes):
Active-Neutral 220V
Active-Earthbar 220V
Neutral-Earthbar 0V
Bandung_Dero wrote:
May 14, 2024, 11:00 am
Was the step down transformer installed by the PEA?
It’s not a new installation,in fact I am at the corner of a rectangle, each side is provided by a tranformer. So it was quite easy to change. I asked to change because the initial line was so poor, in the evening voltage often dropped below 180V. Now we have most of time between 210-225V. We are at 450m of the transformer, I don’t know how many user are on this phase, we have chosen this phase because it was the highest voltage on the rush hour.

The electrician who made the line change, will be back soon, it still has to change the counter for a 45A, so I will discuss this issue with him too.

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Re: Small electric shock on grounded metallic appliances

Post by Bandung_Dero » May 14, 2024, 4:54 pm

Make sure the bonding at the Earth stake is 100% secure, 23 volts wet is not acceptable
and 2.5 amps indicates there is a very high phase imbalance in the network with the neutral floating way above the neutral at the transformer star point.
In my case it turned out to be a faulty transformer which PEA replaced.
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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 15, 2024, 8:18 am

Bandung_Dero wrote:
May 14, 2024, 4:54 pm
with the neutral floating way above the neutral
A somewhat disturbing syntax :D , does this mean that the midpoint resulting from the imbalanced 3 phases is no longer in the center, floating above the physical midpoint?
Bandung_Dero wrote:
May 14, 2024, 4:54 pm
Make sure the bonding at the Earth stake is 100% secure
Yes it is but I don’t know the leght of this rod, maybe install a new one, with a lenght of 2m40, and keep the bonding point outside the ground, something like the picture below

The electrician will come today, I'll see if he's comfortable with this kind of problem.
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Re: Small electric shock on grounded metallic appliances

Post by tamada » May 15, 2024, 8:23 am

Timely reminder for me to check the condition of the ground rod connection for my shed. It's in an accessible but watertight box.

The ground rod for our new, 4-bedroom annex is 2 m long. I will fabricate another accessible but watertight box to make the electricians job a bit easier.
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Re: Small electric shock on grounded metallic appliances

Post by Bandung_Dero » May 15, 2024, 10:57 am

iPa41000 wrote:
May 15, 2024, 8:18 am
A somewhat disturbing syntax :D , does this mean that the midpoint resulting from the imbalanced 3 phases is no longer in the center, floating above the physical midpoint?
If the phase loads are not roughly balanced along the 220 volt transmission lines and without the MEN system the Neutral can float and gets worse the further away the consumer tapping point is from the transformer.
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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 15, 2024, 1:13 pm

Bandung_Dero wrote:
May 15, 2024, 10:57 am
If the phase loads are not roughly balanced along the 220 volt transmission lines and without the MEN system the Neutral can float and gets worse the further away the consumer tapping point is from the transformer.
Hummm, at the transformer, neutral and earth are at the same potential, but not true anymore at the end of the line, that is what I measure at my bonding point. MEN means it should have many bonding neutral with earth along the path. Is that correct ?

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Re: Small electric shock on grounded metallic appliances

Post by Drunk Monkey » May 15, 2024, 1:19 pm

iPa41000 wrote:
May 15, 2024, 1:13 pm
Bandung_Dero wrote:
May 15, 2024, 10:57 am
If the phase loads are not roughly balanced along the 220 volt transmission lines and without the MEN system the Neutral can float and gets worse the further away the consumer tapping point is from the transformer.
Hummm, at the transformer, neutral and earth are at the same potential, but not true anymore at the end of the line, that is what I measure at my bonding point. MEN means it should have many bonding neutral with earth along the path. Is that correct ?
Advise to get a GOOD sparky in to check it all out.

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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 15, 2024, 1:32 pm

Drunk Monkey wrote:
May 15, 2024, 1:19 pm
Advise to get a GOOD sparky in to check it all out.
As said above, one is coming today, but I don’t know if it will be good with this kind of issue.

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Re: Small electric shock on grounded metallic appliances

Post by Bandung_Dero » May 15, 2024, 2:57 pm

iPa41000 wrote:
May 15, 2024, 1:13 pm
Hummm, at the transformer, neutral and earth are at the same potential, but not true anymore at the end of the line, that is what I measure at my bonding point. MEN means it should have many bonding neutral with earth along the path. Is that correct ?
Yes, most all Thai dwellings don't have an earth let alone have it tied to the neutral in their distribution box (if they have that, most around here are just a knife switch and single fuse. :shock: )
In 2002 my neutral was floating so high I installed Dual Pole cct breakers so as I could fully isolate an area.

Edit:-
BTW, just to add, to eleviate your initial problem (being booted off appliances) I suggest you disconnect the Earth - Neutral bond in the consumer box. I have never had it installed not wanting to be the consumer saviour but still having my home fully earthed.
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Re: Small electric shock on grounded metallic appliances

Post by tamada » May 15, 2024, 7:17 pm

BD's on the right track. One of the fixes for our live kitchen appliance issue was to disconnect the ground rod I had set primarily for the back of the house, washing machines, water heater and garbage disposal unit. I have no idea what else, if anything, he cut or installed in the CU. Just taking the cover off to look inside makes me fearful.

There was a revision of the electrical wiring code back about 8 years ago where MEN-compliance is mandatory in new builds and they won't pass inspection if not wired as such. The big problem is the larger amount of really old domestic hookups still connected to the upgraded PEA grids. That and the slow uptake on adopting MEN and a high probability of uninspected new-builds wired with "bad habits". All these serve to make the MEN-compliant farangs house probably the only one in the moobahn and as such, not fully protected due to the other badly wired crap hanging off the local grid.
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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 15, 2024, 8:11 pm

Bandung_Dero wrote:
May 15, 2024, 2:57 pm
BTW, just to add, to eleviate your initial problem (being booted off appliances) I suggest you disconnect the Earth - Neutral bond in the consumer box. I have never had it installed not wanting to be the consumer saviour but still having my home fully earthed.
Now waiting for the sparky visit (tomorrow), but I think it is unlikely that he will provide a solution, as it was said before most all dwellings on the line only have a knife switch with a fuse.
So it could be a workaround.

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Re: Small electric shock on grounded metallic appliances

Post by iPa41000 » May 16, 2024, 7:46 pm

Bandung_Dero wrote:
May 15, 2024, 2:57 pm
BTW, just to add, to eleviate your initial problem (being booted off appliances) I suggest you disconnect the Earth - Neutral bond in the consumer box. I have never had it installed not wanting to be the consumer saviour but still having my home fully earthed.
If I followed correctly, you are now in TT mode. What voltage do you measure between earth and neutral?

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Re: Small electric shock on grounded metallic appliances

Post by Whistler » May 17, 2024, 7:23 am

There is one very simple thing you can try. If the appliance has a 2 pin plug, rotate it 180 degrees and change the polarity.

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Re: Small electric shock on grounded metallic appliances

Post by Bandung_Dero » May 17, 2024, 7:33 am

5.4 Volts - not to bad. But the mains surprised me! 232.6 Volts. This is the 1st time I've tested it since they upgraded most of the power lines throughout the village from 25sq mm to 50sq mm, 2 months ago, was just on 220 prior to that.
We are located about 300 meters from our transformer which is quite large as it feeds some 190 dwellings.
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Re: Small electric shock on grounded metallic appliances

Post by tamada » May 17, 2024, 12:00 pm

Whistler wrote:
May 17, 2024, 7:23 am
There is one very simple thing you can try. If the appliance has a 2 pin plug, rotate it 180 degrees and change the polarity.
Yes, that has worked on some appliances; our chip pan for one. But then they get unplugged and the next time plugged back in the "wrong" way. The chef needed a neon test screwdriver!
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