How to identify presence of an earth electrode

[An Buachaillín Bán]

I have been mulling over your situation as I have recently been in the same predicament. We completed PIR,son 130 homes for a housing association all built between 2005 and 2019.
Our single biggest challenge was the lack of earth inspection pits.The association insisted on "no remedial works ".But sinking earth rods in urban areas is risky and running 10mm earths through nicely decorated homes is undesirable. Yet ,we didn't sink a single earth rod. How did we deal with it?..

1) first ,we established if a rid is present (even if the pit isn't)

2) second, we reminded the employer that the regs allow for the absence of a pit under certain circumstances. (see reg 542.3.4 ,"B" part).

3) we explained how those circumstances can apply to virtually every installation.

4) We ran all of the above by our inspector, who agreed with our approach.

I hope that helps.

Music to my ears! Thank you very much. I'm going to do exactly this. Do you mind if I ask how you confirmed presence of the rod? As I previously stated, I was told to disconnect the Neutralising link and perform a fault loop test at the incoming L+N to the earth bar. If I get a reading around the 200 mark, then I've confirmed the presence of the rod. But I'm wondering, does that 100% prove its the earth rod. Could a parallel path throw up this figure? Sorry if I'm overthrowing and overcomplicated this

 

[Risteard]

It needs someone like @Risteard who is familiar with the ROI rules to properly answer this.

In more general terms, if you think a cable is an earth rod you can isolate it and check its Ra using either a dedicated earth test meter and soil probes, or more conveniently for an already energised installation by doing a Zs style measurement with the E lead to the assumed rod, and the L & N to the supply.

For UK regs it needs to be under 200 ohms to be acceptable, even for 100mA and 30mA RCD that are theoretically good for 500 ohms and 1667 ohms (to 50V at In), to be treated as stable. But care is needed, if you see much below 10 ohms or so it is unlikely to be a rod, more likely bonded to steel works (good for earthing, unusual for most homes) or metallic pipes (can't be trusted going forward, so not permitted as a means of earthing).

If it is above 200 ohms it might be a rod that is in dry soil, or the connection is poor, or maybe is not a rod earth at all! Less likely in the TN-C-S case, but occasionally seen, it might be the supply Ra that is too high as what you really are measuring is the whole loop (supply Ra + transformer Z + cable R1 + load Ra) but usually the sum is dominated by the local rod's Ra.

Apologies I had a busy week last week so am only seeing this message now.

Yes, as stated the electrode is required at every installation. I have always worked on the basis of that if I can't see (and verify) it then for all intents and purposes it doesn't exist. I would install a new electrode even if this is unfortunately not handy to do. And then advise in very strong terms that this must not be covered up!

 

[LastManOnline]

Music to my ears. Do you mind if I ask how you confirmed presence of the rod?

here is where it gets interesting. You cannot ABSOLUTELY confirm that your reading confirms the presence of an earth rod.As you speculate, you could be getting a parallel reading.However ,realistically ,the only metallic services coming in to an Irish home since the 1990,s are....correct ,there are,nt any. .
Secondly and most importantly ,the "powers that be ", SAFE ELECTRIC have chosen to allow that earth rods can be installed without inspection pits.Realistically ,construction companies have naturally taken advantage. And I don,t blame them.And I don,t mind.They do it for economic reasons.But ,realistically, an earth rod sank in concrete will last a lot longer than an earth rod with an inspection pit but lacking proper application of denzo,which is quite common.

As I previously stated, I was told to disconnect the Neutralising link and perform a fault loop test at the incoming L+N to the earth bar. If I get a reading around the 200 mark, then I've confirmed the presence of the rod.

Yes ,that would be the normal approach.

But I'm wondering, does that 100% prove its the earth rod. Could a parallel path throw up this figure? Sorry if I'm overthrowing and overcomplicated this

No ,you are spot on.We cannot prove 100% and yes ,a parallel path could be interfering in your testing ,but it's unlikely.
Since I started to write this post Risteard (Whose comments I appreciate) has made a comment that I think can help us (Irish Sparks) to consider if the current Irish approach (though commendable) is as effective as it might be in offering a genuine solution to the issue of open PEN faults.

 

[An Buachaillín Bán]

here is where it gets interesting. You cannot ABSOLUTELY confirm that your reading confirms the presence of an earth rod.As you speculate, you could be getting a parallel reading.However ,realistically ,the only metallic services coming in to an Irish home since the 1990,s are....correct ,there are,nt any. .
Secondly and most importantly ,the "powers that be ", SAFE ELECTRIC have chosen to allow that earth rods can be installed without inspection pits.Realistically ,construction companies have naturally taken advantage. And I don,t blame them.And I don,t mind.They do it for economic reasons.But ,realistically, an earth rod sank in concrete will last a lot longer than an earth rod with an inspection pit but lacking proper application of denzo,which is quite common.


Yes ,that would be the normal approach.


No ,you are spot on.We cannot prove 100% and yes ,a parallel path could be interfering in your testing ,but it's unlikely.
Since I started to write this post Risteard (Whose comments I appreciate) has made a comment that I think can help us (Irish Sparks) to consider if the current Irish approach (though commendable) is as effective as it might be in offering a genuine solution to the issue of open PEN faults.

Certainly food for thought. Really appreciate the feedback. Thanks

 

[UNG]

Secondly and most importantly ,the "powers that be ", SAFE ELECTRIC have chosen to allow that earth rods can be installed without inspection pits.

Do they give a reason for this decision

But ,realistically, an earth rod sank in concrete will last a lot longer than an earth rod with an inspection pit but lacking proper application of denzo,which is quite common.

Do you have any evidence to support this given the corrosive qualities of concrete

 

[James]

set concreate is not corrosive as far as i know, if it was then all the re-bar in buildings would be at risk?

 

[LastManOnline]

Do they give a reason for this decision

No.The reg simply states that rods sank in "public areas" such as footpaths may be covered in after the initial inspection.Our understanding is that the "powers that be" are concerned about anything that might be utilised as a "trip hazard".

Do you have any evidence to support this given the corrosive qualities of concrete

Yes.Metal covered in concrete lasts for decades.From personal experience I have had to dig up rods that were buried in concrete (they also had denzo tape).They were in perfect condition.The rods exposed to air though (as they often are in a pit) are prone to rusting.

 

[pc1966]

Yes.Metal covered in concrete lasts for decades.

There is an article about that here:

Cement & Concrete FAQ - American Cement Association

Your basic cement and concrete questions answered by qualified experts.

www.cement.org

It states:

Although steel’s natural tendency is to undergo corrosion reactions, the alkaline environment of concrete (pH of 12 to 13) provides steel with corrosion protection. At the high pH, a thin oxide layer forms on the steel and prevents metal atoms from dissolving. This passive film does not actually stop corrosion; it reduces the corrosion rate to an insignificant level. For steel in concrete, the passive corrosion rate is typically 0.1 µm per year. Without the passive film, the steel would corrode at rates at least 1,000 times higher

I think that is the reason you must have something like 5cm of concrete around any embedded steel so that high pH environment is preserved.