How to identify presence of an earth electrode

[An Buachaillín Bán]

Hello to all you fine folk out there.

I have a question regarding earth electrodes.

I've had two periodic inspections/EICRS recently, where I haven't been able to locate the earth electrode. I am guessing they are installed but have possibly been covered over by new patio extensions and other ground works. The reason I say this is that in both cases, they are small 3 bed houses. I have identified my neutralising links, and there are 3 other 10sq earth cables at the MET at the distribution boards. I know two are doing the bonding of gas and water.
So I'm guessing the other is going to the earth rods.

Is there a way I can test to find out if an earth rod is installed? I remember a guy telling me a while back to disconnect the neutralising link and perform a test across main L, N and E? If result I'd up around 200M ohms then there is an earth rod but I'm not too sure about all this.

Any help I'd really appreciate
Thanks

 

[alasdairmp]

It's to do with with reducing the "Touch voltage" under an Open PEN fault when all bonded meralwork in the home becomes live.
There is a popular misconception that the rod can act as a " back up" when the DNO,s neutral breaks ,but this is not realistic with a standard single earth electrode.

I do not genneraly approve of these "double Earth" connections. (a) as stated above a single Earth Rod is not adequate as a back-up Earth for a PME connection (see (c) below); (b) it often (usually?) increases Stray and Net currents in the area causing higher magnetic fields (UK residential avg is 20 - 80 nT and should not be above 200 nT for health related reasons; (c) I have come across many installations where this extra connection causes 1 - 20 A or more to flow (and not from that property, but to balance the network system voltages). The worst I found was 355 A at an large office on a N London industrial estate due to the external armouring that was carrying combined N & E being broken and all return current going through the steel structure into the Earth and back to the nearby substation (about 30 metres from the building) but causing high magnetic fields (about 5 microtesla) which made the CRT computer displays "wobble" - which was why I was called in. OK, no-one uses them now so that "canary alarm" no longer exists. I feel that if this double Earthing bonding is in place, the clamp-meter readings for Each Earth cable should be measured and should be low (ideally well under 1 Amp). The DNO had to dig up and replace the supply cable in the case above. Afterwards the Earth current was about 30 mA.

 

[UNG]

It's to do with with reducing the "Touch voltage" under an Open PEN fault when all bonded meralwork in the home becomes live.
There is a popular misconception that the rod can act as a " back up" when the DNO,s neutral breaks ,but this is not realistic with a standard single earth electrode.

A lot would depend on where the DNO neutral was broken if the DNO neutral was broken at an underground joint with a number of properties beyond that point then there could be a neutral which is given an earth reference by a number of rods at the properties beyond the neutral break point there is also all the other unquantifiable parallel earth paths to consider as well

 

[LastManOnline]

It may also give an rcd a chance of working with an open pen fault.

Unfortunately not.Another peculiarity of the TNC-S system is that an open PEN fault actually renders your rcd,s ineffective in protecting you should you touch any live metalwork.
The rcd does,nt detect the fault current flowing through you as an imbalance.Your only protection will be in having a well insulated floor which thankfully ,many modern homes have.

 

[mainline]

Unfortunately not.Another peculiarity of the TNC-S system is that an open PEN fault actually renders your rcd,s ineffective in protecting you should you touch any live metalwork.
The rcd does,nt detect the fault current flowing through you as an imbalance.Your only protection will be in having a well insulated floor which thankfully ,many modern homes have.

The post was related to TT not TNC-S

 

[LastManOnline]

I've had two periodic inspections/EICRS recently, where I haven't been able to locate the earth electrode. I am guessing they are installed but have possibly been covered over by new patio extensions and other ground works.

Any help I'd really appreciate
Thanks

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.

 

[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.