Earth rod spacing

[uksparks]

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.

 

[telectrix]

if installing 2 rods, space the by 1.5 x the rod length. so if using 2 6ft. rods, 9 ft. spacing.

 

[uksparks]

Thanks, seems I wasn't a millions miles out in my thinking.

 

[HappyHippyDad]

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:

 

[Geordie Spark]

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:

What do these "meters" you speak of measure???

 

[HappyHippyDad]

What do these "meters" you speak of measure???

Very Un-British of me.. sorry :blush5:

 

[trev]

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:

Yes, you would put it a couple of metres away from the building.
The ones right next to buildings are generally worthless because they are in an area which is usually filled with builder's rubble.
You'd run the cable in accordance with the regs.
You can't say that " a (as in only one) long thick rod will do" you may well need several
There's a lot of confusion and mystery over TT systems which is really unnecessary, they aren't really that difficult. Especially domestic ones.
My own home is on a TT and it has an Ra equivalent to a TN-S, my record is 0.29. Others have even beaten that.

 

[Deleted member 72666]

That's a very good reading, how many rods did you need for that and how deep did you go Trev?

 

[trev]

First rod gave me around 140, second one gave me about 30 so I thought how low can you go. Knocked the third one in and it plummeted. Was well happy
I've got 2 knocked in under the floorboards in me house, 2 x 5/8 coupled together

 

[Deleted member 72666]

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

 

[trev]

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

Depth is the key Stan, that 0.29 will have dropped a little more once the soil consolidated around the upper parts of the rods and my home will have too. I've not tested it since the day I rewired it, might do it next time I have a day off.
Even if both values haven't dropped I know for a fact that they'll never fluctuate because they're in virgin soil which is out of reach of winter/summer temperature variations.

 

[Eddiesparks]

Neutral tail into henley block. Take an earth off that. TNCS BINGO LOL!!

 

[guest119]

A Kango breaker set to chisel (ie not drill) with a star point chisel is great for driving them in.
Easier than the old "when I nod my head, hit it".
Then you can get rod after rod in then grinder it at the height you want for the enclosure.

boydy

 

[Marvo]

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.

 

[uksparks]

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:

Ive bit yet put a rod in, it's all hypothetical at present! Do you use a three lead and prong test thing what it called, eRth rod test probe kit to test it or do you just measure at the DB?