Earth Rods

[RickH]

2 parts to an earth rod Q.

On advice on another thread - I need to install an Earth rod when a new TT circuit is installed.
What size rod do I need ? Looking at some of the the information I have it seems to be that an 8' rod is needed ? ..... how is this achieved if you use for example the standard TLC 2/8" (9mm) rod which is only 1.2m long ?
It has no threaded section so you can't join them together like you can with 5/8" rod
Or is 4' (1.2m) long enough for domestic install ?

The 2nd part is where every post I have found gives a different answer - the protective earth cable from the rod (in its inspection box) will be 6491X single cored green/yellow PVC insulated, and carried in flexible conduit to the termination point about 2m in total. So at no time is it in contact with the ground though for about 1m the flexible conduit is buried, as it routes to the termination point.
I see cable size stated from 2.5 to 16 mm2
The TT circuit it is protecting is 6mm2 32A (via SWA underground cable) RCD protected
What is the correct size earthing conductor to use ?

Or as some time in future there may be a need to export PME ... should I use 10mm ?

 

[EFLImpudence]

It seems what you are asking is: "Please tell me everything I need to know to be an electrician".

Outside power is not a DIY job.

 

[RickH]

The connections will be done by an electrician, as will (Part P) certification... I just want to get the trench, cable laid in & rod installed. (which he is happy with me doing)
It is after all a DIY forum .... so doing the physical labour part & purchasing of materials.

 

[EFLImpudence]

Then you must ask him how he wants it done.

 

[RickH]

He won't be at site before I ask him to be there ...
Obviously, you don't want to help, fair enough - your choice.
.... as this is DIY forum, it would seem the place to ask for help.

 

[EFLImpudence]

Then ask him to be there.

I have told you - outside power is not a DIY job and as you have an electrician you must do what he wants not someone on the internet.

 

[ericmark]

I would start up the paddies motorcycle and knock in first rod, then un-reel the two lengths of cable seem to remember 15 meters and 30 meters approx, connect to the meter, and press test and write down reading, move the closest probe in a meter and out a meter and retest each time if the three reading don't match you need to test over a longer distance, if they do your looking for a reading with Domestic of around 60Ω if not low enough screw on the adaptor and fit another rod, again use the paddies motorcycle to knock the rod in, and so on.

When I was doing this we wanted 8Ω and it needed between 4 and 8 rods, it was a two man job as the paddies motorcycle is not light. We hired the meter, and test probes and cable, if you already have power you can compare with the DNO earth using a loop impedance meter.

Cable sizes are listed in BS7671, mine is not up to date, so better you look yourself.

I knocked in earth rods for 4 months, not a nice job, seems I was ear marked for the job as I had zero potential, really got it as over 6 foot tall, and standing on a box with a paddies motorcycle is not really an option. With a site over one mile long and ½ mile wide no problem, but for domestic hard to get the distance from the earth rod to test, likely in some one else's garden. Also a problem finding a location for the rod where you know there is no metal services underneath it or close.

 

[flameport]

What size rod do I need ?

If you must use rods, then the length and quantity is determined by the conditions of the ground they are to be installed in.
In some locations a single 1.2m rod may be suitable.
In others, much longer rods will be required. Or multiple rods of various lengths at appropriate spacings.
They and anything else connected to this TT installation must be located far away from any other earthing system. Far away meaning at least 5m, and in most cases 10+m

It has no threaded section

That's because it's the wrong product. Far too thin and can't be extended in any way. Also far more difficult to drive into the ground as there is no way to fit a cap onto the end, and also no satisfactory way to attach a clamp for the wire.

I see cable size stated from 2.5 to 16 mm2

2.5mm² is the minimum size for a buried copper earthing conductor which is protected against mechanical damage and corrosion.
16mm² is the minimum size where it is not mechanically protected but is protected against corrosion.
If it's not protected against corrosion, much larger sizes will be required.
The size also depends on the expected fault current, but that's not likely to be a significant consideration for a small domestic installation.

 

[Taylortwocities]

Outside power is not a DIY job.

Whssign

• Taylortwocities
• 16 Jul 2016

What he said

 

[EFLImpudence]

I knocked in earth rods for 4 months, not a nice job, seems I was ear marked for the job as I had zero potential,

 

[RickH]

If you must use rods, then the length and quantity is determined by the conditions of the ground they are to be installed in.
In some locations a single 1.2m rod may be suitable.
In others, much longer rods will be required. Or multiple rods of various lengths at appropriate spacings.
They and anything else connected to this TT installation must be located far away from any other earthing system. Far away meaning at least 5m, and in most cases 10+m


That's because it's the wrong product. Far too thin and can't be extended in any way. Also far more difficult to drive into the ground as there is no way to fit a cap onto the end, and also no satisfactory way to attach a clamp for the wire.


2.5mm² is the minimum size for a buried copper earthing conductor which is protected against mechanical damage and corrosion.
16mm² is the minimum size where it is not mechanically protected but is protected against corrosion.
If it's not protected against corrosion, much larger sizes will be required.
The size also depends on the expected fault current, but that's not likely to be a significant consideration for a small domestic installation.

Thank you for your reply.
No other rods within 10m.

I have asked the electrician who will certify if he can visit to confirm rod size needed, await a response.
Maybe he has an SDS driver tool, would certainly make it easier to drive in If not can you get a screw on cap so it can be hammer driven ?

Bought a 5/8 rod a way, maybe I will need another.

 

[flameport]

No other rods within 10m.

It's not about other rods, it's anything connected to the TNCS or TNS supply, including metal gas pipes, metal water pipes, the supply cable and so on.

 

[RickH]

The incoming water & gas are plastic they do not extend past the house (I put them in so know where they are)
No other services are there other than the external garage TT supply and its local earth rod.
Being a self build ... I know what went where.

I have made a request to electrician to come measure (& install) earth rod.

 

[ericmark]

Where I work we have detailed plans of the site, we thought we knew where every drain ran, we were having problems and it was decided we needed another drain, when we came to prepare we found a manhole covered by grass, the drain must run under the railway line, which went in 1903, so no one could have put in the drain after that date without our knowledge, although trains stopped running 1956 to 1963, it was still a railway line, so should have know about any drain laid, specially since this was clearly a foul drain having seen things floating by, but we didn't, we could have easily driven an earth rod straight through it. It is on the plans now. However it was not metallic, so it may have cause a problem for the house it served, but would not have affected the earth rod.

 

[RickH]

I would start up the paddies motorcycle and knock in first rod, then un-reel the two lengths of cable seem to remember 15 meters and 30 meters approx, connect to the meter, and press test and write down reading, move the closest probe in a meter and out a meter and retest each time if the three reading don't match you need to test over a longer distance, if they do your looking for a reading with Domestic of around 60Ω if not low enough screw on the adaptor and fit another rod, again use the paddies motorcycle to knock the rod in, and so on.

When I was doing this we wanted 8Ω and it needed between 4 and 8 rods, it was a two man job as the paddies motorcycle is not light. We hired the meter, and test probes and cable, if you already have power you can compare with the DNO earth using a loop impedance meter.

Cable sizes are listed in BS7671, mine is not up to date, so better you look yourself.

I knocked in earth rods for 4 months, not a nice job, seems I was ear marked for the job as I had zero potential, really got it as over 6 foot tall, and standing on a box with a paddies motorcycle is not really an option. With a site over one mile long and ½ mile wide no problem, but for domestic hard to get the distance from the earth rod to test, likely in some one else's garden. Also a problem finding a location for the rod where you know there is no metal services underneath it or close.

Thanks for explanation. Pity you weren't closer to Neath ... I'd get you to do this job