Earth rod spacing

uksparks · Mar 22, 2014

Hi,

Just a general question, I have never installed an earth rod so don't have any experience in them, but would like to think I know the basics before I come across one I have to install.

My question is, presumably I would be correct in thinking the 3/8 rods are not worth the time and should be not sold, and only 5/8 should really be used, put at least two in connected vertically, depth is best I understand, should I need to install another rod to help bring the reading down, is there a recommended distance the second rod should be from the first one or would putting it a few inches away be ok?

My initial thoughts are that it would be ideal to locate it the same distance away that the first one is long, so if its a 4ft rod, put it at least 4ft from it?

And keep them a couple of meters away from the house where possible. Someone mentioned to me that putting a think 1000mm drill into the ground can help drive it in easier.

I did find a good thread on here this morning about exporting PME, or extending the equi-potential zone so to speak and needing to TT the remote end in some circumstances, it did confirm my thoughts, but made interesting reading.

Richard Burns · Mar 22, 2014

For a general TT system the difference in resistance from the addition of line conductor will be minimal compared to the rod resistance so taking an EFLI at the DB will be as accurate as required for domestic use.

GLENNSPARK · Mar 22, 2014

happyhippydad said:
I am in similar position UKsparks! The Ra is around 350ohms from what I can remember so I'll be putting an additional rod in. What Ra do you have? Would you really put it a couple of meters away from the house, they generally seem to be right next to it. It does make sense to keep it away from the house..How would you run the cable the couple of meters away?

Guidance note 8, section 2 is a good read although I would have no idea of the level of the water table or how to calculate the resistivity of the soil! It does give 'probable values' for soil resistivity types though which you could use to determine what length and diameter rod you need.

I'm probably getting a bit carried away though.. A thick long rod will do! :smile5:

you bet it does.

Think about it....if you put it right next to a building then alls the rod`s going to do is hit all the building rubble/foundations and whathaveyou...

GLENNSPARK · Mar 22, 2014

Marvo said:
The larger diameter the rod the better within reason, the thin rods have much less surface area and they're much more likely to bend and deviate from vertical when they're hammered in. If you need to knock in 2 or 3 or 4 rods to get a decent Ra then it's better to couple them together to make a single deep rod rather than knocking them in as separate rods.

We don't usually worry about being too close the building, by the time you've gone down 6, 8 or even 10 meters with the rod as long as you've not hit anything that stops the rod going down it makes very little difference to the Ra reading if there's builders rubble near the top. The one thing I do worry about is hitting pipes or cables so we normally dig at least the first 2-3 feet to make sure there's nothing there.

yes....caus your looking for stability...in all conditions...

a shallow rod will only be good in the wet.....the deeper you go the more you get under the soil surface....which will dry out when the sun comes out....

depth is key with TT....

uksparks · Mar 22, 2014

So the rule here is to bang in in nice and hard and nice and deep and you will be rewarded for it.

- - - Updated - - -

And don't bang it in too close to home as you don't want to be pulling it out again.

GLENNSPARK · Mar 22, 2014

uksparks said:
So the rule here is to bang in in nice and hard and nice and deep and you will be rewarded for it.

- - - Updated - - -

And don't bang it in too close to home as you don't want to be pulling it out again.

you dont want complaints from the neighbours either...

jamie-spark · Mar 23, 2014

Geordie Spark said:
What do these "meters" you speak of measure???

Geordie
your pm mail box is full

Engineer54 · Mar 23, 2014

stantheman said:
Wow! What a great place,never thought of them going there. I imagine the readings wont fluctuate much either during the year.

Actually, ''NOT'' such a great area to place earth rods. Far better to place earth electrodes externally where rain can keep the surrounding soil wet/damp. The damper the surrounding soil, the better will be the contact between soil and electrode, and better will be the Ra values obtained.

Engineer54 · Mar 23, 2014

Marvo said:
The larger diameter the rod the better within reason, the thin rods have much less surface area and they're much more likely to bend and deviate from vertical when they're hammered in. If you need to knock in 2 or 3 or 4 rods to get a decent Ra then it's better to couple them together to make a single deep rod rather than knocking them in as separate rods.

We don't usually worry about being too close the building, by the time you've gone down 6, 8 or even 10 meters with the rod as long as you've not hit anything that stops the rod going down it makes very little difference to the Ra reading if there's builders rubble near the top. The one thing I do worry about is hitting pipes or cables so we normally dig at least the first 2-3 feet to make sure there's nothing there.

Unfortunately in the UK, you'd be lucky to get a single 2.2m 5/8'' rod, and very lucky indeed if you get an electrician to couple two together and get 2.4m!! Far more likely to get a non extendible 2.2m thin twig lol!!

I'll warrant that no-one here has ever driven a rod down 10 metres, or even 8 metres come to that!!

GLENNSPARK · Mar 23, 2014

Engineer54 said:
Unfortunately in the UK, you'd be lucky to get a single 2.2m 5/8'' rod, and very lucky indeed if you get an electrician to couple two together and get 2.4m!! Far more likely to get a non extendible 2.2m thin twig lol!!

I'll warrant that no-one here has ever driven a rod down 10 metres, or even 8 metres come to that!!

not in my world..

telectrix · Mar 23, 2014

serious question, though. what do you do when the rod hits rock at 3 ft.?

GLENNSPARK · Mar 23, 2014

telectrix said:
serious question, though. what do you do when the rod hits rock at 3 ft.?

nest, tapes, grids or mats...

anything to increase the CSA of contact...together with careful consideration of siting....

Marvo · Mar 23, 2014

telectrix said:
serious question, though. what do you do when the rod hits rock at 3 ft.?

We use a case-hardened tip that screws onto the first rod before it gets hammered in, 8 times out of 10 it will go through loose rock when used in conjunction with a jack hammer with an SDS Max rod driving attachment.

[ElectriciansForums.net] Earth rod spacing

GLENNSPARK · Mar 23, 2014

Marvo said:
We use a case-hardened tip that screws onto the first rod before it gets hammered in, 8 times out of 10 it will go through loose rock when used in conjunction with a jack hammer with an SDS Max rod driving attachment.
View attachment 23821

still didn`t help the zulu`s at rorke`s drift though did it...:83:

ipf · Mar 23, 2014

Marvo said:
We use a case-hardened tip that screws onto the first rod before it gets hammered in, 8 times out of 10 it will go through loose rock when used in conjunction with a jack hammer with an SDS Max rod driving attachment.
View attachment 23821

Is that for a veldt tip pen ? :38: