Live to Ground (as in the SOIL) voltage 220V !

old_sparky_RE · May 7, 2012

At the moment I’m working overseas at a BFPO address in the Middle East. The climate is warm (30-35 at the moment) and dry.
While conducting a visual inspection of a distribution board I thought I had stepped on an ant nest as my right foot was 'tingling' as I was working away.
On looking down there’s nothing there so I asked the lad with me to switch the meter on (Fluke) and push the test probe into the ground near my foot as I put the other probe on to L1 then 2, 3…… the meter read 220V !!
So we got another meter (Megger) and recorded 218V, after stabbing the probe round and using a trailing lead at a distance of around 10m we had 0V.
Now the area is saturated with earth rods coming from multiple buildings, the wiring systems are a mixture of TN-C-S and TN-S in that area.
The supply cable passes IR and I’ve been assured the generator has a N-E link fitted.
My question is why would none compacted sand/fine gravel be able to be a perfect zero potential to give this reading and why have I never come across this before (but then I’ve never gone L1 to Ground (soil/grass) in the UK) this cannot be normal, so how has it happened and what is the solution?

Des 56 · May 7, 2012

Here is my uninformed stab in the dark

Large earth currents flowing through a earth grid can cause a earth rise potential reducing with distance

It seems to me there may be large discharge currents through the nearby buildings earth spikes which are bringing your earthing,( which is linked via supply neutral), to a potential well above your own local ground conditions,you may be measuring lives to true earth locally,but zero where the discharges are located

What are your measurements between your earth and local ground, and your earth and the distant ground point

Knobhead · May 7, 2012

Is the building steel framed? If it is it could be your local earth point.

If you were stood with your feet separated you could have been feeling the effects of a ground voltage gradient. You did say you tested at a distance so that shows a gradient was present.

barnzi · May 7, 2012

Sounds like there could be a broken neutral somewhere else and the neutral current is returning through the ground stake for that panel.

old_sparky_RE · May 8, 2012

Thank you for your replies and sorry for not replying earlier.
The voltage between the MET and all local groung rods was 200v +, due to the nature of the building switching off the power is not going to happen ( i was lucky to have the power off for 2min to do an IR test) and a waver has been signed by the 'customer' saying they are happy to leave it!!!!
The buildings are all brick with bonded concrete reinforcing and have there own Earthing rings run round the building with added 'free' earth spikes for the equipment inside dotted all over the place!
I was able to test with a clamp meter and all rods have between 2mA and 300mA running down them.
But as the "get out of jail free card" has been signed the job has finished.
I'm still baffeled by the fact the ground can carry a voltage when the 'soil' is fine sand/very fine gravel (like course brown sugar), zero moisture content but still 200v 4m from the board before it starts to trail off !!!!

Darkwood · May 8, 2012

Its the minerals within the soil/sand that allow conduction wet or dry, do remember pure water is a good insulator but its all the pollutants, minerals etc in it that makes it conductive, a little concerned about the Waver the customer signed and how much clout it holds, the customer isn't the qualified electrician here, you have shown a 200v from True Earth to MET and also up to 300mA flow, this has easily got the potential to kill anyone making the bridge between the Earths and in a court of law exactly how much will that waver protect you.... i hope it is worded correctly and clearly states the risks, if not the customer may just play dumb at any hearing saying i didn't really understand it as im not an electrician!
I would make sure your waver is clear, expresses the risks and is signed by more than just the boss but his partners and anyone in charge of maintenance of the site, and be inclined to lock the room off and signed over the key(s) to anyone who has signed the waver also leaving a warning sign clearly visible about the existing hazard.

old_sparky_RE · May 8, 2012

These wavers are signed on an almost daily basics for things that would see you doing 8-12 years in the UK! The waver is signed by a rep from that country’s government…. and that’s the end of it (the company’s not UK), a bit like when there was Crown immunity from prosecution.
If I had my way I’d also lock out and rectify however this area is classed as ‘War Winning’ and will never be shut down.
It’s one for the books for sure.

Thanks for the input gents.

Darkwood · May 8, 2012

Well beats any waver i suggested, and see why your can now sleep better knowing you are out of the loop

Engineer54 · May 8, 2012

Without being able to investigate myself, i'm just wondering if these rods have been connected to separate supply systems, where the rods haven't been spaced correctly outside there sphere of influence (eg, sphere's of influence over lapping) You could then get interaction, depending on what sort of equipment and loads these electrodes have been connected too. It sounds to me as this site has a lot IT type loads etc, ...Yes??

Just because the top layer(s) of soil are dry, if the rods (what size and what length are they??) have been driven deep or coupled to drive deep, then there is every chance you have penetrated ground water. We have encountered this from Saudi (Riyadh) to Libya (Benghazi) so don't always be fooled about arid or dessert areas always being ''dry as a bone'' ...lol!! Could even be an old dried-up salt lake under there, which would be compacted and give exceptionally good Ra readings ...lol Found them too, in the Middle East, Quite a few in Cyprus too... lol!!

old_sparky_RE · May 8, 2012

Yes the rods have been pepper potted all around the buildings with some having their own rings buried around them, and on top of that some of the buildings are glorified Faraday cadges. I've found out that the Ground rods are NEC 10footers and that area is an area where they can be driven to that depth because of the geology.

I can't say what the equipment is in these buildings is but there is a 'robust' shoot to kill policy to protect what goes on in there !!! So I can't say YES but I won't say no either

Engineer54 I think you are right with the dried up salt lake, or as the area lies at the bottom end there may be an underground stream there or just ground water (we had snow here last month!!) less than the 10foot down for the rods to hit.

So the solution would be to use shallow buried ground mats then so as not to interact with the moisture / salt lake as a pathway, space is also limited? As I've said earlier this won't be fixed as a waver has been signed.