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

 

[UNG]

What you refering to as neutralising links or has some sort of TNCS setup been created tying the neutral to the earth rod

If you can't locate the earth rod and more importantly check the condition of the connection at the earth rod then the only real option is to FI it

 

[An Buachaillín Bán]

What you refering to as neutralising links or has some sort of TNCS setup been created tying the neutral to the earth rod

If you can't locate the earth rod and more importantly check the condition of the connection at the earth rod then the only real option is to FI it

Hi UNG,

Sorry these installations are TNCS arrangements, so yes houses are neutralised. I'm wondering if a test can be done to determine if an earth rod is in place. I would install another earth rod only that it isn't easy to do so. Houses have concrete path all around and plans show services such as gas, water and electricity out front.
Going out the back isn't really an option as customer won't pay for this.

 

[mainline]

Hi UNG,

Sorry these installations are TNCS arrangements, so yes houses are neutralised. I'm wondering if a test can be done to determine if an earth rod is in place. I would install another earth rod only that it isn't easy to do so. Houses have concrete path all around and plans show services such as gas, water and electricity out front.
Going out the back isn't really an option as customer won't pay for this.

Why would you install an earth rod if it's a TNCS earthing system ? What is the Ze?

 

[An Buachaillín Bán]

Why would you install an earth rod if it's a TNCS earthing system ? What is the Ze?

In Ireland, it is a requirement to have an earth rod installed even on TNCS systems. I'm not 100% on that but fairly confident. And seeing as I had to record this on my testing sheet when carrying out the inspection, I have to either install one (which isn't an option at present), or at least confirm the presence of an electrode

 

[UNG]

Hi UNG,

Sorry these installations are TNCS arrangements, so yes houses are neutralised. I'm wondering if a test can be done to determine if an earth rod is in place. I would install another earth rod only that it isn't easy to do so. Houses have concrete path all around and plans show services such as gas, water and electricity out front.
Going out the back isn't really an option as customer won't pay for this.

So given that this is a requirement I assume the rod has to be installed to give a resistance below a given level in the regulations as a loss of the neutral while the installation is still "earthed" by the rod could create a dangerous situation

I would suggest the only way you are likely to find the rod is using a Cat and Genny if you put a tone on the earth lead and scan round the property you sould be able to narrow down the rod position

If you can't locate the rod or get a reasonable resistance reading then unfortunately the customer has little or no choice but to pay for a new rod

 

[davesparks]

Why would you install an earth rod if it's a TNCS earthing system ? What is the Ze?

Because that is what is required by the regulations the OP is working to. In Ireland, and most of the rest of the world as far as I know, a TNCS supply is required to have an earth electrode connected to the MET. This is one area where the UK is lacking.

What you refering to as neutralising links or has some sort of TNCS setup been created tying the neutral to the earth rod

Under Irish regulations the neutralising link is the link between neutral and earth, this is the responsibility of the installer and not the DNO. Installations are required to have an earth electrode connected to the MET which is then connected to neutral by the neutralising link.
So yes it is some sort of TNCS and it is better than a TNCS supply in the UK as you get an earth rod at the end of every service cable and not just at each end of the distributing main with a few dotted in between.

 

[pc1966]

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.

 

[mainline]

Because that is what is required by the regulations the OP is working to. In Ireland, and most of the rest of the world as far as I know, a TNCS supply is required to have an earth electrode connected to the MET. This is one area where the UK is lacking.

It's recommended in Bs7671

 

[davesparks]

It's recommended in Bs7671

Great but this thread is about an installation in Ireland where it is a requirement.
The point I am also making is that TNCS supplies in the UK could be improved if it was a requirement here too.

Also, where in BS7671 is it recommended? Other than the note in the swimming pools section and prosumer installations I don't think it is.

 

[mainline]

Great but this thread is about an installation in Ireland where it is a requirement.

So you have said a few times after the o/p had already stated the fact.

Also, where in BS7671 is it recommended? Other than the note in the swimming pools section and prosumer installations
I don't think it is.

Regulation 411.4.2 now recommends an additional connection to Earth, by means of an earth electrode in accordance
with Chapter 54, is made to the main earthing terminal.

 

[LastManOnline]

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?

Instead of disconnecting the neutralising link I would disconnect the unknown remaining 10mm earth ,which you can be virtually certain is going to the earth electrode.Carry out an fli test on it and you will likely get a reading somewhere between 100 to 300 ohms.
Though strictly speaking there should be an inspection pit present ,the reality is ,is that in at least 50% of cases there is,nt.

 

[LastManOnline]

Why would you install an earth rod if it's a TNCS earthing system ?

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.

 

[mainline]

It's to do with with reducing the "Touch voltage" under an Open PEN fault when all bonded meralwork in the home becomes live.

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

 

[An Buachaillín Bán]

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

Could you explain this a little further for me please?