Earth Rod - DIY

[JohnW2]

As I said, in the draft, the reg is silent on this issue ...

542.1.201 The main earthing terminal shall be connected with Earth by one of the methods described in Regulations 542.1.2.1 to 3, as appropriate to the type of system of which the installation is to form a part and in compliance with Regulations 542.1.3.1 and 542.1.3.2. Additionally, there shall be an earth electrode, supplementing any earthing facility provided by the distributor, in accordance with one of the requirements of Regulation 542.2.3, to prevent the appearance of a dangerous touch voltage in the event of the loss of the main connection to Earth.

≤30Ω would preclude my TT earth electrode (other than in the wettest of conditions) and, I would have thought, a substantial proportion of all domestic TT electrodes.

 

[Taylortwocities]

I am fitting the earth rods on saturday and my plan was to fit 2 under the living room floor.

That is not a good location. The subsoil is likely to be quite dry there. You need an outside location.

Do not install two rods unless you understand the implications. Two rods can interfere with each other (I’m putting this simply) and you can end up with a worse, rather than a better impedance as a result.
Better to screw two rods end to end. Be prepared to drive 8ft into the ground. Some rods have screw threads at the ends and you can buy a coupler.
https://www.tlc-direct.co.uk/Products/TLER58.html

https://www.tlc-direct.co.uk/Products/TLER58CUP.html

But, as above, DIY earth electrode = bad idea.

 

[JohnW2]

Do not install two rods unless you understand the implications. Two rods can interfere with each other (I’m putting this simply) and you can end up with a worse, rather than a better impedance as a result.

For my education, could you possibly provide a somewhat 'less simple' explanation (assuming the two (or more) rods are in pretty close proximity to one another)?

Better to screw two rods end to end. Be prepared to drive 8ft into the ground. Some rods have screw threads at the ends and you can buy a coupler.

Indeed they do. However, if things remain true to the DPC, we are soon to be hit with ...

542.2.8 Where an earth electrode consists of parts that must be connected together, connections shall be made by welding, pressure connectors, clamps or other suitable mechanical connectors.

... which I imagine will preclude the use of 'screwed together' rods, don't you?

Kind Regards, John

 

[Mottie]

I banged two screwed together rods when I had a supply put into my workshop. I think they dropped the rods off about a week before and told me what to do. I also had to dig a hole down on my side of the footings. Mind you, that was in 1987 so things may have changed since then!

 

[ban-all-sheds]

As I said, in the draft, the reg is silent on this issue ...
≤30Ω would preclude my TT earth electrode (other than in the wettest of conditions) and, I would have thought, a substantial proportion of all domestic TT electrodes.

Is there any guidance on how to comply with the parts you quoted?

There is in 722, and it may be wrt that that I read a figure of 30Ω. But then doing the guidance calculation in A722.3 (17th) only spits out 30Ω for an Iinst of 3.33A.....

Do it for an Iinst of 30A (not unreasonable when including an EV charging) and they might as well simply ban the use of PME in that situation.

 

[JohnW2]

In the draft, the regulation in question (542.1.201) is silent on that issue. However, I would assume that the implication is that it would have to be as effective as would be required if it were providing the sole (TT) earth for the installation.

 

[Taylortwocities]

For my education, could you possibly provide a somewhat 'less simple' explanation (assuming the two (or more) rods are in pretty close proximity to one another)?

I did save an extract froma very involved document (see below). When i get a bit of time, I'll try and find a link to the whole enchilada

Simple stuff, eh? bang in a few rods, what could go wrong?

EDIT: Can't find the full tech document at the moment. There is an intersting explaination and result graphs in this article

 

[securespark]

... which I imagine will preclude the use of 'screwed together' rods, don't you?

542.2.8 Where an earth electrode consists of parts that must be connected together, connections shall be made by welding, pressure connectors, clamps or other suitable mechanical connectors.

 

[securespark]

Be prepared to drive 8ft into the ground.

Don't forget your seatbelt!

I'll try and find a link to the whole enchilada

I got that for you:
https://22657-presscdn-pagely.netdna-ssl.com/wp-content/uploads/2016/10/Whole-Enchilada.jpg

 

[securespark]

To be serious for a minute, the DNO do have a duty of maintenance on an earth terminal provided by them.
Sometimes, it is difficult or impossible to say whether the installation has been fitted with an earth terminal. I have seen conduit like yours several times, some were TT and others TNS and one, IIRC was TNC-S.

What is the other end of that conduit like?


Edited for clarity.

 

[JohnW2]

542.2.8 Where an earth electrode consists of parts that must be connected together, connections shall be made by welding, pressure connectors, clamps or other suitable mechanical connectors.

Indeed, but don't you think that the implication is that simply screwing two rods together (not in the same league as welding etc.) will probably not be adequate to satisfy that reg?

If you think that it might be acceptable, what methods of 'connecting together' do you think would not be acceptable?

Kind Regards, John

 

[Taylortwocities]

I guess there’s no issue if the screw joint is “accessible”..

 

[SimonH2]

... it is a twin motor compressor, the biggest one Clarke do on a normal domestic supply.

Is that the 2x3hp or 2x4hp ? A mate has had one of the (IIRC) 2x3hp ones for a good few years - and never had any complaints (we can't see any light flickering when it starts up). Had "a few problems" over the years, and Machine Mart came out to look at it when it first went in due to starting problems. Running fine now though.

You probably need permission from your DNO, because if you don't, and the use of it disrupts your neighbours' supplies, you'll be in trouble.

Well if he has the same "luck" as my mate, then there'll be no problem.

Do not install two rods unless you understand the implications. Two rods can interfere with each other (I’m putting this simply) and you can end up with a worse, rather than a better impedance as a result.

It took me a while to work out what you were saying there - it comes across differently to what I think you meant. 2 rods cannot have a higher combined impedance than 1 alone - as is corroborated by your later post.
I assume that what you are actually saying is that 2 short rods could have a worse impedance than a single rod of twice the length. I could well see that being the case given that the top layers of soil can be of distinctly variable effectiveness - so putting the extra length deeper down is going to give a better impedance.

 

[JohnW2]

I did save an extract froma very involved document (see below). When i get a bit of time, I'll try and find a link to the whole enchilada

Many thanks.

Simple stuff, eh? bang in a few rods, what could go wrong? ... There is an intersting explaination and result graphs in this article

Thanks. I understood that (because of the interaction of fields) the use of multiple rods would result in less than 'pro rata' reduction in impedance, but what surprised me was your statement ....

Two rods can interfere with each other (I’m putting this simply) and you can end up with a worse, rather than a better impedance as a result.

If the resistance of each of the rods (used alone) were the same, say r, then that equation in what you posted would reduce to:

R = r/kn

... hence one could only end up with overall impedance (R) being greater than the impedance of one rod used alone (r) if (k*n) were less than than 1. However, given that n must be at least 2 and (the article says) k cannot be less than 1, that situation cannot arise.

However, there is something which currently makes no sense to me about the sample values of 'k' given in what you posted. They say that k=1.25 for a≥2l and that k becomes approximately 1 when a≥4l - i.e. that k decreases as the spacing of the rods increases, reaching 1 (the lowest permitted value) when the spacing reaches about 4 times the rod length. That would mean that the combined resistance of multiple rods would increase as the spacing increased - which seems to make no sense. In contrast, the graph is the article you linked to shows, as one would expect, combined resistance decreasing as rod spacing increases.

Can you make any sense of those quoted 'k' values? Am I missing something, or getting my sums wrong?

In any event, maths aside, it surely makes no sense in terms of intuition, common sense or physics that connecting a second rod to a first one can possibly result in the impedance to earth increasing, can it?

I would think that the bottom line is this. Whilst using multiple rods will not result in the degree of reduction of impedance that one might have 'expected', particularly if they are close together, there will always be some reduction resulting from adding extra rods - and, particularly for a DIYer, I would think that it would be preferable to hammer in two or more 4ft rods than to try to hammer in one 8ft one.

Kind Regards, John

 

[JohnW2]

I guess there’s no issue if the screw joint is “accessible”..

Maybe not - but would you regard 4 feet underground as 'accessible'?

Maybe the rods could be joined with an MF JB

Kind Regards, John