Earth Rod Resistance is high

[weston]

Hello All,

I hope somebody can give me some guidance.
I have an installation that is a TT system, the area is very sandy, down the hill from the distribution board is a lake, approx 70 Meters away. The rise is about 10 metres from the lake to the level of the DB.
Next to the DB enclosure I have installed an earth rod 5/8 extendable, this is 3M deep in the ground, reading 612 ohm.
I have installed 9 x 1.2M (11M approx) 5/8 rods straight down approx 5M from DB enclosure, reading 658 ohm.
I have installed 3 lots of 3 x 1.2M (3.6M) 5/8 rods stright down at a distance of 3M apart in a triangle arrangement down at the lake level, reading 512 ohm.
I can't seem to get the reading down low enough.

Any ideas before I install enough rods to raise the copper and steel content of the area.

 

[weston]

Go for the deep rod answer mate as its likely to be more stable n all........

I think your right, I will try and go deeper, sledge hammer works great for knocking them in...

 

[grimysparks80]

Ive always fancied knocking on a customers door with a sledgehammer in my hand and saying "hello luv. Im here to sort your electrics" lol

 

[weston]

I do that to people that don't pay...

 

[weston]

Another variable is your test meter accuracy

I thought that, fitted new batteries, then check it against my check box (as I do every month). But no my meter is accurate...Shame, could have been a quick fix....

 

[Guest123]

Have a look here..... Thomas & Betts | Europe & click on the 'furse' logo.


Have you considered any of the other types of earthing methods......tapes, mats etc.

Depth is the best way of achieving decent Ra though, especially on sandy ground. Try larger rods and keep screwing them together until you get an acceptable result, perhpas some ground conditioner would help too.

 

[Marvo]

Have a look here..... Thomas & Betts | Europe & click on the 'furse' logo.


Have you considered any of the other types of earthing methods......tapes, mats etc.

Depth is the best way of achieving decent Ra though, especially on sandy ground. Try larger rods and keep screwing them together until you get an acceptable result, perhpas some ground conditioner would help too.

I agree there's no substitute for depth. Over the years I've experimented with different thickness rods and it seems to make no difference. We use a 17mm rod if I'm going down < 13 meters and a 22mm rod if I think we'll need to be deeper than that. The only reason I opt for a 22mm rod is that they don't deviate from straight as much when you knock them in. I use a 2 meter length of hardened steel bar to start the hole in the right direction, I knock it in then twist it back out again to leave a nice straight starter hole for the rods. 2 meters is usually long enough to get past any building rubble etc which can cause the rods to deviate from going straight down. I once installed a 17mm spike that we obviously started knocking in at 90 degrees to the ground but on the 5th rod we connected it surfaced almost pointing directly upward, 6 meters away in the middle of the guys driveway. Also when connecting your rods together the couplings should be grease filled and screwed together very tightly.

With ground conditioners, salts and electrolytes, they might help a little during installation but a year later you often need to reapply to get a decent reading. We've never had very good results with these and it's cheaper to give the surrounding ground a good soaking for a few hours if you need a temporary improvement.

We also use mats if it's a new building. They work well but they need to be in the compacted ground under the foundations. Mats have always proven to be a very stable earth for us, I've retested installations that we installed several years previous and they often have a better Ra result than they did just after the building was completed.

 

[DNS1]

What sort of reading is likely if you just chucked the rod in the lake?!

 

[aaelectric]

how would you test the earth rod was good enough if there was no power??

 

[MarkieSparkie]

how would you test the earth rod was good enough if there was no power??

With either the Fall of Potential, Dead Earth or Clamp On methods, using a dedicated Earth Resistance Tester.

 

[ezzzekiel]

please please dont listen to most of the avise DO NOT keep driving down the, eventually you will hit the centre of the earth and everything will leak out then were screwed

 

[Guest123]

Like this, using a proprietory earth electode test instrument.

Earth electrode resistance testing

The method to carrying out this test.
1) Using a proprietary tester.
The test unit has three connections. The first is attached to the electrode under test, the second to an auxiliary potential electrode or ‘spike’, and the third to an auxiliary current electrode.

The positioning of the auxiliary electrodes is critical to the test and positioning is dependant upon the length of the electrode under test. The current electrode is placed at a distance ten times the test electrodes length and the potential electrode is placed in a direct line midway between the two. At this point a reading is taken and noted. Two further readings are now taken. The first with the potential electrode placed 10% nearer the current electrode and the second, with the potential electrode placed 10% nearer the electrode under test (from its original position).

The average of the three readings is taken as the electrodes resistance (as long as all three readings are within 5% of one another). If they exceed 5% the test must be repeated with the distance of test and auxiliary electrodes increased.

 

[LlandrilloSpark]

I've done some work in sunny Rhyl last year on the sea front properties, they literally sit on the beach, they are TNS but I couldn't get anything below 10 ohms on any property!

 

[richy3333]

Might be worth trying to speak to the DNO guys that did their earthing? From what you said it sounds like you might need to use a digger to get earth material deeper? It could be less hassle in the long run and less labour intensive than banging in the earth rods?

I had a similar situation on a caravan site and we buried 30m of earth matting nice and deep, away from the pitches to get a viable earth.

Does anyone know where you can get an SDS drill attachment for putting in earth rods. Heard it talked about but not seen one?

 

[Guest123]

Makita ground rod driver | Shop makita ground rod driver sales & prices at TheFind

 

[aaelectric]

So there is another tester to test earth rod??
As i live in london we never use tt systems but this temporary board onsite commercial they have ran a new pme system but say as its temporary we have to use tt earth??
Howmuch are the testers and isit worth it for this one job??
how far do you go with earth rod?. I have hit into ground with a hammer but its goes half way then stops, As i carnt read the ze how do i no if dno will connect power?