Life expectancy of a ground rod?

[frizbeedog]

We were able to pull this out of the ground during a recent service change for a manufactured home. Sometimes you can't yank em out for an inspection.

View attachment 1476

Notice the deterioration?

View attachment 1477

And in other spots?

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Way back when, I would reuse these and add a second rod. But the first time I saw this I changed my ways. This particular rod is about 30 years old.

 

[mdshunk]

There were long-term tests being conducted near Las Vegas (I think) on the lifespan of various types of ground rods. I understand that this test had gone on for years, but had to be abandoned because development finally made its way out to the field where the rods were installed. I forget who was doing that test.

 

[BackInTheHabit]

Ashes to ashes, and dust to dust.

 

[mdshunk]

Here's the report the report from the study I mentioned:

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

 

[charlie]

I forget who was doing that test.

The IAEI was doing the tests and there were several locations that were developed across the country. I looked on their site but found no information. I my memory serves me correctly, the testing is still in progress but some sites may be shut down.

Well Marc, you beat me with your response. However, the IAEI testing is for the effectiveness of various types of electrodes in a range of soils and installation styles. <Edited to add the last paragraph.>

 

[frizbeedog]

A current flow problem?

A current flow problem?

The first comment from a co-worker was that there was current flowing throught the rod to have done that.

The service pedestal was what I refer to as a two piece. It is a Meyers if I remember right. The top section (housing the main) plugs into the lower section (utility lugs) via knife blades which are known for pitting, arcing and corrosion. Homeowner complains of flickering lights, power drop offs etc., and one of these types services, when I see one, is the likely culprit.

 

[mdshunk]

The first comment from a co-worker was that there was current flowing thought the rod to have done that..

A good ground rod will always pass some current. The better the ground rod, the more the current. I don't know if that helped the disintegration or not. There will always be some corrosion of metal things in the ground. The higher the soil acidity, the faster the corrosion. This is why buried propane tanks and tower legs are connected to anode bags. The anode bag material is easier to "eat" than the tank or the tower legs. One could connect an anode bag to a grounding electrode system if this caused him great concern.

 

[frizbeedog]

A good ground rod will always pass some current. The better the ground rod, the more the current. I don't know if that helped the disintegration or not. There will always be some corrosion of metal things in the ground. The higher the soil acidity, the faster the corrosion. This is why buried propane tanks and tower legs are connected to anode bags. The anode bag material is easier to "eat" than the tank or the tower legs. One could connect an anode bag to a grounding electrode system if this caused him great concern.

But due to the poor connection of the grounded conductor through the knife blade attachments, I was leaning towards more than usual current.

Anode bag. New term for me. Thanks.

 

[Karl H]

GREAT!! The CMP is going to read this and require 4 ground rods in 2011. Thanks buddy! :grin: No really, That is a very good observation.

 

[iwire]

Ground rods are so old school, now is the time of the concrete encased electrode.

 

[Karl H]

Ground rods are so old school, now is the time of the concrete encased electrode.

I completly agree.

 

[don_resqcapt19]

I wonder if as the rod corrodes the ground around the rod becomes more conductive as part of the process? In other words does the ground resistance go down as the rod corrodes...at least until there is no more metal.
Don

 

[Frenetic]

As it corrodes, the resistance increases. It's just a matter of surface area versus contact with Earth. Corrosion effectively decreases the contact area.

Edit: Oh, that's why concrete encased electrodes are so good. Concrete effectively increases the contact area, which in turn, decreases the resistance. Moreover, concrete protects the electrode from corrosion.

 

[iwire]

As it corrodes, the resistance increases. It's just a matter of surface area versus contact with Earth. Corrosion effectively decreases the contact area.

I doubt it is as straight forward as you make it sound.

As the rod corrodes the earth around it likely becomes more conductive.

 

[Frenetic]

I doubt it is as straight forward as you make it sound.

As the rod corrodes the earth around it likely becomes more conductive.

Well, remember, the resistance of a ground rod is a product of its surface area. Copper corrosion decreases that surface area. If you've ever seen a corroded rod, you'll notice that the radius has decreased, which in turn, decreases the surface area.

The oxidation of copper itself doesn't decrease the "resistance" of the earth around it. Most oxides are actually rather resistive.

 

[jrannis]

As it corrodes, the resistance increases. It's just a matter of surface area versus contact with Earth. Corrosion effectively decreases the contact area.

Edit: Oh, that's why concrete encased electrodes are so good. Concrete effectively increases the contact area, which in turn, decreases the resistance. Moreover, concrete protects the electrode from corrosion.

I like the use of the contact with the earth comment. Around here they have to install plastic sheeting under the concrete slab. I dont see much earth contact from that type of installation.

 

[iwire]

Well, remember, the resistance of a ground rod is a product of its surface area.

Yes that is for sure.

Copper corrosion decreases that surface area. If you've ever seen a corroded rod, you'll notice that the radius has decreased, which in turn, decreases the surface area.

That is also without a doubt true.

The oxidation of copper itself doesn't decrease the "resistance" of the earth around it.

The ground rods are generally copper plated steel rods, I suspect the iron does not disappear it moves into the earth around it likely lowering the resistance of the soil.

Most oxides are actually rather resistive

Again true, but are they more resistive then the native soil around the rod?

 

[LawnGuyLandSparky]

One day, I'll relay the story of the city site inspector at a treatment plant. The entire job was PVC coated galv. She wanted to know why the ground rods weren't PVC coated, and seemed quite proud of herself when she discovered the bare metal...

 

[Frenetic]

The ground rods are generally copper plated steel rods, I suspect the iron does not disappear it moves into the earth around it likely lowering the resistance of the soil.

When a metal corrodes, it doesn't leach away in pure form. So, if the Iron corrodes from a ground rod, the soil doesn't get an infusion of Iron, but instead gets a nice sprinkling of Ferric Oxide (or rust). The corrosion itself is an oxidation process, so it's now an oxide: Ferric Oxide, Copper Oxide (patina), all of which exhibit high resistivity.

That's why corroded connections aren't very conductive.

 

[iwire]

That's why corroded connections aren't very conductive.

I agree, but with a connection your starting with a relatively small resistance so any corrosion has a detrimental effect.

The soil around a rod is already a high resistance so in my opinion it is up for debate if the corrosion will hurt or help.

All my point was has been is there is more to this then just the loss of surface area. :smile:

A ground rod does almost nothing in any case for those of us that work under 600 volts, it's 'connection' to earth is poor at best.