Why did this ground rod fail?

[Crossy]

I'm at a loss here, below is a photo of the top 300mm of a 2.5m copper-clad steel ground rod.

We had a power surge earlier in the week, during a big storm so likely lightning related, we lost two satellite boxes, the dish LNB and a few LED lights as well as the gate controller.

Checking the electrics over today revealed the rod reading over-range (>2k ohms) on the earth resistance test (I have a proper earth resistance meter).

The rod just pulled out by hand, or at least the top foot did, the rest is still in the ground (if it still exists that is).

Anyway, all I've done is washed the clay off the rod.

The exposed steel is not rusted, matt grey in colour, the copper cladding is still intact to about 150mm below the ground level.

It wasn't an expensive rod, but it's only been in the ground 2 years (Bangkok clay).

Supply is MEN with neutral ground straps on every 3rd pole.

A closer view of the corroded end.

Any bright ideas?

The new rod is a good quality copper clad rod (860 Baht), I just don't want it to go the same way so quickly, measures 2.8 ohms.

[bankruatsteve]

Just tossing out a thought... I wonder if galvanic reaction due to bonding with your structure?

[Crossy]

Just tossing out a thought... I wonder if galvanic reaction due to bonding with your structure?

It certainly looks galvanic doesn't it. If it were anywhere near a DC traction railway I'd be saying 'stray current' but the nearest DC power metro is 50km away.

Rod is steel where it's been eaten, re-bar is also steel (ok it's encased in concrete).

Hope it's not been eating away at our re-bar!!

[RichCor]

Acidic soil maybe? I wonder if you need to dig a well and to a soil backfill with GEM.

Earthing System components

And I usually won't post links from the 1900's, but...

Copper Ground Rods: Lightning Protection Information

Edit: Finally found a technical paper with some failure descriptions...

Steel Grounding Design Guide and Application Notes

Edited October 30, 2014 by RichCor

[Crossy]

Excellent stuff Rich

I have no idea what our soil pH is, but a quick Google says that Thailand has generally acidic to strongly acidic soils.

So why can one only buy solid copper ($$$$$) or copper clad steel rods?

I understand Ireland has acidic soils and actually prohibits copper clad rods, insisting instead on hot-dip galvanized steel.

I can see I will have to monitor our new rod carefully.

[harrry]

What makes you think that the rest is still in the ground. Did you actually see the electrician put the rod all the way in. Much easier to cut it and put a short one in.....and copper is so saleable.

[Crossy]

What makes you think that the rest is still in the ground. Did you actually see the electrician put the rod all the way in. Much easier to cut it and put a short one in.....and copper is so saleable.

555 Thanks Harrry.

Yes, the installation was witnessed and photographed by my good lady whom I trust implicitly

[harrry]

What makes you think that the rest is still in the ground. Did you actually see the electrician put the rod all the way in. Much easier to cut it and put a short one in.....and copper is so saleable.

555 Thanks Harrry.

Yes, the installation was witnessed and photographed by my good lady whom I trust implicitly

Thats fine then. I had to stop mine cutting the thing off short.

[Crossy]

What makes you think that the rest is still in the ground. Did you actually see the electrician put the rod all the way in. Much easier to cut it and put a short one in.....and copper is so saleable.

555 Thanks Harrry.

Yes, the installation was witnessed and photographed by my good lady whom I trust implicitly

Thats fine then. I had to stop mine cutting the thing off short.

I will say that when I pulled out 12" of rod I did think 'bloody sparks ripped us off' but a hunt through the photos of our house build and Wifey's assertion changed my mind.

I will be digging out the rest of the rod at the weekend just in case the camera lies

[bankruatsteve]

Doesn't really matter how long it was. Something happened to corrode it bad. Maybe inferior product?

[IMHO]

I think all possible causes have already been discussed - so nothing to add, except thanks for the scare - I'll be pulling mine and checking them this weekend

[longball53098]

Crossy, glad you have this issue to report about and not one of us amateurs. With all the electrical pitfalls we have to look for here now you come along and add soil testing and rod checking to the list. What next?

For those of us without the expensive test equipment how does a concerned homeowner test the rod without pulling it out. And on a working electrical system is it safe to disconect the ground cable and pull the rod out? What precautions are needed?

[Crossy]

It is indeed scary.

I disconnected the rod at the consumer unit (easier than getting the clamp off) and only when it showed high resistance did I physically check the rod, when it came out in my hand I nearly had kittens.

How to check your rod without any expensive kit? Not easy I'm afraid

Turn off your power before disconnecting the rod. Give the rod a good tug, if it won't come out chances are it's not in the same state as ours was, clean up the clamp, rod and cable and re-attach.

WARNING The following process is dangerous. Keep children and pets safely corralled, do not work alone, do not touch the rod whilst testing.

You can get a good idea if your rod is serviceable using a 15W tungsten light bulb. Click on the Spoiler to show.

With the power off disconnect the cable going to the rod inside your distribution board.

Connect one side of the lamp to the cable that goes to the rod.

Very carefully, dab the other side of the lamp onto the incoming live supply.

If the lamp lights full brightness you can be reasonably confident that your rod is OK.

WARNING Go back and read my warning.

[Tywais]

Odd about the Iceland requirement of galvanized steel as it has the worse life time based on the below paper. Note the similarity with your photo but after 10 years. My suspicion is the Ph factor of the soil is acidic.

https://www.erico.com/public/library/fep/strike/LT0540.pdf

[John_Betong]

I haven't read all the links in depth but immediately thought back to my marine days and "sacrificial nodes".

http://en.wikipedia.org/wiki/Galvanic_anode

Seems like yours gave up the ghost for Halloween

Edited November 1, 2014 by John_Betong

[ksamuiguy]

If you can pull the ground rod out, the installation is no good.

We use 5/8" copper clad galvanized 1.8 meter minimum length on all installations.

Remember to leave the rod exposed so it can be checked during your regular maintenance checks..

If you have a megger the resistance should be below 10 ohms.

Don't use multiple ground rods with out knowing the rules.

If you have a lightning system installed, make sure the ground rods are as far a part as possible.

Do Not use the telephone ground for your electrical system.

Dig down and see if there is evidence of the rod being vaporized, a possibility if the lightning strike was very near.

This the reason we use 5/8 rods 1.8 meters long minimum.

[BobTH]

You say you have the proper instrument to test your ground rod. I assume you mean you are using an earth resistance meter such as a vibroground or a megger, these are the only way to get a true earth to ground measurement. You would need to do a test called " Fall of potential measurement test or three pin method."

Also if you have an interference problem with stray current your ground rod would have a positive potential measurement using a reference electrode. The current discharge areas of your ground rod should look bright and shinny like new metal, looking at the photos you posted it looks to me like that might be your problem.

I would suggest that you also test the new rod after it has been in the ground a while, I could have a drastic increase in potential to earth in a short time if your problem is still occurring.

[Barin]

The soil conductivity is what is important for good quality grounding system.

The rods are not so good for the grounding system because the surface area of the rod in contact with soil is relatively small.

And if the rod is badly corroded the conductivity will be very poor. Which results in a poor grounding of your equipment.

The best way to do, dig a flat hole in the ground, not so deep, 50 cm. enough, with the size of approximately 150 x 150 centimeters.

Scatter 10 kilograms or more of salt over the bottom surface of the hole.

Place horizontally a large metal sheet about 140 x 140 centimeters made of copper on the bottom of the hole with a copper braid soldered to the sheet and bury it.

Pour water over the hole after it is already filled.

During the dry season don't forget to pour water once a week.

[tigermonkey]

Don't know if your problem is similar to one I had years ago, but there seems to be many similarities. Ground rod ( copper clad steel) was completely gone at about 10" below ground level 2-1/2 years after installation. Soil was highly acidic with high peat content. A friend. who had previously owned a commercial electric company, suggested a Ufer ground. I was skeptical, but he installed it for me - 3 naked steel rods in round casing of concrete ( about 1 ft diameter X 6 ft deep). Resistance is still very good after more than 10 years.

Edited November 1, 2014 by tigermonkey

[DGS1244]

Think the lightning strike was a lot closer than you know. Possible that there is something else bonded to the ground and the step potential had caused the disintegration of the copper. Have seen it before but nor for a long time.

[RigPig]

Crossy, what did you use to test the ground resistance? An earth loop impedance tester? Did you do the calculation? Have you MEN'd the swirchboard? As you know it is the depth, not how much metal is in contact with the ground, they debunked that one years ago.

Corrosion is always a problem and I have always wondered if there could be some galvanic action caused by ground rods using 2 dissimilar metals used in a "salty" soil. Lead sinkers left in an aliuminium boat comes to mind.

This is interesting, and not something one would normally look for....

[Crossy]

I have a Robin KTS-1630 installation tester https://www.bsria.co.uk/instrument/view/product/kts1630/?tab=downloads which amongst other things does 3 and 4 wire earth resistance tests. So yes , it is the proper kit.

New rod is 5/8" copper clad steel 2.5m long.

Measures about 2.8 Ohms (pretty good for a rod, our soil is very wet being only 2m above normal river level).

Supply is MEN (and the neutral is grounded every 3rd pole).

Not measured the soil pH but Thailand is noted as being acidic in general.

Rest assured, it will be monitored with interest.

[Strangebrew]

Since you mentioned water You might try encasing it in cement Your soil way to much acidity I don't know if going stainless steel would be off help. But silver is a better conductor. Should hold up better than copper.

[RigPig]

I have a Robin KTS-1630 installation tester https://www.bsria.co.uk/instrument/view/product/kts1630/?tab=downloads which amongst other things does 3 and 4 wire earth resistance tests. So yes , it is the proper kit.

New rod is 5/8" copper clad steel 2.5m long.

Measures about 2.8 Ohms (pretty good for a rod, our soil is very wet being only 2m above normal river level).

Supply is MEN (and the neutral is grounded every 3rd pole).

Not measured the soil pH but Thailand is noted as being acidic in general.

Rest assured, it will be monitored with interest.

NICE meter, you obviously didn't buy that in Thailand LOL.

I have one of those 3 foot long Thai rods the electrician at my mates house was going to use, I think it is steel / copper clad, I am going to get a bucket of salt water or maybe vinegar and see if there is any voltage produced between the inner and outer and a couple of other tests I can think of, just out of shear curiosity...

[harrry]

I have a Robin KTS-1630 installation tester https://www.bsria.co.uk/instrument/view/product/kts1630/?tab=downloads which amongst other things does 3 and 4 wire earth resistance tests. So yes , it is the proper kit.

New rod is 5/8" copper clad steel 2.5m long.

Measures about 2.8 Ohms (pretty good for a rod, our soil is very wet being only 2m above normal river level).

Supply is MEN (and the neutral is grounded every 3rd pole).

Not measured the soil pH but Thailand is noted as being acidic in general.

Rest assured, it will be monitored with interest.

NICE meter, you obviously didn't buy that in Thailand LOL.

I have one of those 3 foot long Thai rods the electrician at my mates house was going to use, I think it is steel / copper clad, I am going to get a bucket of salt water or maybe vinegar and see if there is any voltage produced between the inner and outer and a couple of other tests I can think of, just out of shear curiosity...

These new fangled meters.. You are all getting soft. No muscles to wind the handle of the Megger.

[Mrjlh]

Looked like very aggressive galvanic action me also. Both acidic and salinity action taking place. Per a couple of articles, the reaction is increase if the latent electrical currents are present. If you have had lightening strikes over the two years that could account for the rapid deterioration. Per a pdf article I attached lighting puts out over 18,000 amps one the average strike. The other link goes more into the galvanic reactions. Maybe these will help.

http://www.copper.org/resources/properties/protection/underground.html

grounding and materials(1).pdf

[Jdietz]

Corrosion will also be quick if there's a DC component on your ground. Can you check on that?

[RigPig]

I have a Robin KTS-1630 installation tester https://www.bsria.co.uk/instrument/view/product/kts1630/?tab=downloads which amongst other things does 3 and 4 wire earth resistance tests. So yes , it is the proper kit.

New rod is 5/8" copper clad steel 2.5m long.

Measures about 2.8 Ohms (pretty good for a rod, our soil is very wet being only 2m above normal river level).

Supply is MEN (and the neutral is grounded every 3rd pole).

Not measured the soil pH but Thailand is noted as being acidic in general.

Rest assured, it will be monitored with interest.

NICE meter, you obviously didn't buy that in Thailand LOL.

I have one of those 3 foot long Thai rods the electrician at my mates house was going to use, I think it is steel / copper clad, I am going to get a bucket of salt water or maybe vinegar and see if there is any voltage produced between the inner and outer and a couple of other tests I can think of, just out of shear curiosity...

These new fangled meters.. You are all getting soft. No muscles to wind the handle of the Megger.

Harry I do know what you are saying but, it's hard to take the readings when you are cranking the handle.

A megger will not do an Earth Loop Impedance test, the older models required driving "test" rods at different distances, the new (Fluke) ones are like a clamp tester and will even indicate if you have leakage and how much (among other things), You can't beat technology mate, especially it it makes life easy......

However I am not sure this "digital" everything is the way to go, analog meters can tell you things digital meters can't, try testing your cars indicators with a digital meter hahaha.....

[nithisa78]

This was very good. After one career in communications and eletronics, I still learned more today. It will help me keep my mouth shut the next time I think I know something.

Thank you.

[Commercial Diver]

Looks like it did it's job, carrying a huge charge to ground .. the fact that it's dead - maybe it carried the charge into a damp spot where proper passing on of the current was impeded, and the thing fried .. curious. Any other ideas - I'd like to know, too ..