Best Ze for Earth Rod

[bigd]

Dear All,

What are the 'tricks' to a good earth rod impedance?

If I'm getting 30-40 ohms am I doing OK?

Am I flogging a dead horse trying to get it any lower?

I know the regs recommend under 200 ohms but what's the general concensus on what constitutes a good reading?

 

[Silly Sausage]

We have a TT Guru on here.
I'm sure he'll be along later and enjoy answering your question!

 

[SPARTYKUS]

We have a TT Guru on here.


I'm sure he'll be along later and enjoy answering your question!

Lol
he wouldnt be in China would he !

 

[johnboy6083]

Im not the TT guru, but here goes:

The easiest way to get the lowest Ra (resistance of the electrode, and cable to it) is to go deep,. The deeper the better. This is because as you go deeper, the moisture content in the soil increases, and becomes less dependant on the weather conditions. Also the ground wont freeze.

If you hit rock, the the other option is to use another electrode position. This must be sited at least the distance equal to the depth of the longest of the electrode away. So say you have an electrode of 6m depth. The nearest you could place another electrode is 6m away.
You could lay tapes or mats ect to try and lower your reading, but youd have to dig a deep hole, and you probably wouldnt get a much better result than a deep rod. Rod thickness doesnt have a great influence on the resistance, neitrher does the copper content. Rust doesnt have much of an effect either, as it will conduct better than the soil around it. As long as the connection from the cabl;e to the rod is non corroding, then thats ok. We use Denzo tape/paste at work.
The last resort is soil conditioners, but they will undoubtably be expesnive (ive never used them), and i reckon thatb you would have to reapply at set intervals to maintain a low Ra.

 

[vernam616]

Isnt it anything over 100 ohms requires investigating now?

 

[KFH]

I would be happy with 30-40 ohms as long as there is no risk of drying out, deeper is better as suggested before. I have put rods into sandstone by drilling holes and putting rods in through a bentonite slurry. Got Ze down to 70 Ohm but with bonding to metal work included it came down to less than 50 Ohm. 20kg of bentonite cost approx £20 and I still have lots left, will probably have lots left when I retire. Don't forget that the supply earth resistance can be a max of 21 Ohm but it is not uncommon to get a Ze below 10 Ohm.

 

[Engineer54]

Im not the TT guru, but here goes:

The easiest way to get the lowest Ra (resistance of the electrode, and cable to it) is to go deep,. The deeper the better. This is because as you go deeper, the moisture content in the soil increases, and becomes less dependant on the weather conditions. Also the ground wont freeze.

If you hit rock, the the other option is to use another electrode position. This must be sited at least the distance equal to the depth of the longest of the electrode away. So say you have an electrode of 6m depth. The nearest you could place another electrode is 6m away.
You could lay tapes or mats ect to try and lower your reading, but youd have to dig a deep hole, and you probably wouldnt get a much better result than a deep rod. Rod thickness doesnt have a great influence on the resistance, neitrher does the copper content. Rust doesnt have much of an effect either, as it will conduct better than the soil around it. As long as the connection from the cabl;e to the rod is non corroding, then thats ok. We use Denzo tape/paste at work.
The last resort is soil conditioners, but they will undoubtably be expesnive (ive never used them), and i reckon thatb you would have to reapply at set intervals to maintain a low Ra.

That's a fair enough answer for a domestic installation Johnyboy!! ...lol!! Though i doubt if he's gone down 6m though!! If he had, he'd probably be a lot lower than the 40 ohms he has now, if the ground soil type is half decent...lol!! But your right Depth is is going to give the biggest gain, not only to the Ra value, but also to the stability of the system...

Also remember that extended rods will always improve over time as the ground compresses around the areas where the couplers have made a slightly larger diameter hole, during driving the rods in.

You only need to maintain chemical enhances, as these tend to leech away over time, You shouldn't need to re-apply the likes of Bentonite, and magnotite (Furse-chem), which are both a surface area increaser, not enhancers as such, but they would rarely be used in a domestic situation...

 

[alarm man]

here we go again..
:lipsrsealed2:
ps.read the can...very apt

 

[nickblake]

Best Ra reading ive ever had was 0.89 ohms and was on a house which had a soak away where the rod was installed which was connected to a utility room waste ,it had 2 1 meter rods joined together and had an earth rod pit to make access easier never got dry and always had some soapy water entering it which helped the readings

 

[Silly Sausage]

Lol
he wouldnt be in China would he !

or Cyprus.

If Greece goes bust, what happens to one half of Cyprus?

 

[robsparky1975]

Have you made a enquiry to the dno to see if pme is available? as it seems that they are converting a lot of supplies.

 

[Engineer54]

or Cyprus.

If Greece goes bust, what happens to one half of Cyprus?

Probably bailing them out...lol!! You haven't heard then, they have recently found large oil deposits just off the coast of eastern Cyprus!!

 

[Silly Sausage]

Hahahaa...Turkish side???

 

[Engineer54]

haha!! So they think, but they are not getting a look-in on this one, ...It's still internationally classed as an illegal State...

 

[Silly Sausage]

haha!! So they think, but they are not getting a look-in on this one, ...It's still internationally classed as an illegal State...

Watch out for those pale faced Icelandicers, fish are running out these ways