Just installed an earth electrode where just the materials cost a whopping £1500.00

Soil is a very sandy and a single electrode was getting me around 600ohm EFLI. The installation was for a small Caravan Park.

After some conversations with Furse I burried 14meters of copper tape 1 meter deep, and used some of their FurseCEM Conductive Aggregate.

Even then I only got it down to 146ohm.

Just sharing and wondering if anybody else had used anything similar.

I'm just wondering if that is justifiable.

Andy

From what perspective, Andy, what's in your head? Just the money, money vs results, etc.?

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Eur Ing Graham Kenyon CEng MIET

Straight into conversation at the highest level

It is a caravan park, apart from distribution circuits we will be looking at putting everything on 30mA RCD's, the improved electrode reading may not make a significant improvement on the performance of a 30mA RCD.

However the improved electrode is now highly dependable by the sound of it and allows the use of a RCD rated above 30mA also the use of time delayed S-type on the distribution circuits, allowing discrimination between devices creating a better performing installation.

It depends really on the size of the installation and layout of circuits.

Andy

The distribution circuits are protected by a 100mA S Type RCD. Each hook-up has its own 30mA RCD.

I did consider getting the earthing arrangements at the origin "upgraded" to PME with local rods at the hookups, but the DNO said it was not available so did not give any further consideration.

The customer was made aware of the costs before any work commenced and I was surprised that he gave me instruction to proceed.

Just out of interest how much is that a bag?

We use Marconite. But even then, thats a last resort, after elaborate earth rods or matting.

What about a couple of steel girders down vertically into the ground ?

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

For a single dwelling a dual 30mA RCD consumer unit on the 600ohm rod could be justified, I can see why you have done it this way for this installation.

If you had fifty rods around the site you may have achieved similar results with resistances in parallel, however it would have been a comparable cost.

Legh will do the maths!

Andy

That's very kind of you. Which maths would you like?

1/ Ra < 50/Ia (IAn)

or

2/ R(ave).- R(max.dev.) / R(ave.) *1.2

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

Sum of resistance in parallel for fifty rods at 600 ohms a piece.

Rt = R/N = 600/50 = 12 Ohms

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E & OE

What is this - a level 2 maths test?

R(per rod) / No.of Rods = 12 Ohms (seems rather low.)

Why not use a couple of very long rods rather than 50 * 1.2m 12mm2 ones?

1.2m rod = 600 Ohms
2.4m rod = 360 Ohms
4.8m rod or 2 *2.4m (parallel) = 216 Ohms
or 4* 2.4m rods (parallel) = 133 Ohms
9.6m rod or 2* = 130 Ohms.

All values are approximate .

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

A rod per pitch outlet box and yes, 12 seems low in reality.

Now, Sparkiemike went horizontal at a metre depth as opposed to depth with a long rod, it's sandy soil so should we head down looking for the wet patch and will it make any real difference?

Andy

Depth from what I understand gives a better result (greater % reduction). Coupled with some soil additive around the electrode will reduce it still further.

Legh

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Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."

I agree with legh that a longer electrode is better, i would have also linked mine together with 25x3 bare copper tape. Rather than insulated cable

General agreement then that Sparkiemike has completed a pukka job then?

Andy

And why waste the money on a 75mm2 conductor when a thin bit will do?Is this a joke? When Ra is 100 ohms the connecting cable really doesn't matter, it never carries ant current to speak of anyway.

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David
CEng etc, don't ask, its a result not a question!

Despite the soil being very sandy I could not get more than one 1.2m in at a time, in one location the whole rod went in (with a lot of persuasion) and about 10-15cm of the second one and no futher. A second location I could only get 3/4 of the rod in. The soil was litered with ironstone perhaps that was hindering progress.

A third location I could push the rod in with my hand, I think this area was backfill from the orginal building work. The instrument could not even get a EFLI reading. Joined the three up and EFLI was 410ohm

I paid £84

Salty water works a treat - pour that over the soil ontop of the tape. Theres also other chemicals you can add dependant of soil type. Had to do this quite a ferw times earthing the star point of a 11KV/415 transformer. But aslong as you have a wide trench then good quality soil all round the tape (even if you have to get some from elsewhere) then you will be fine. You can then backfill the rest of the trench normally. Make sure the soil is compacted quite heavily before testing.

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From SMD's to 132kV... ive had a go!

Richard Talmage, LCGI EngTech TMIET