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Earth Resistance

02/15/2017 2:15 AM

we have to reduce the earth resistance to below 1 OHM. Now the reading is 18OHM. How can i optimise t below 1 Ohm?.

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#1

Re: Earth resistance

02/15/2017 2:48 AM

Depending on soil conditions, it may be as simple as adding water. A whole lot more information is needed. What type of earth grounding system do you have? Single copper rod in the ground, an earth pit or grounding thru concrete rebar? And what are your soil conditions like in the area of your earth ground, wet, dry, rocky, sandy, clay, etc?

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#2

Re: Earth resistance

02/15/2017 3:05 AM

You may be at the mercy of your local authority as to what they will allow, but one common method is to add more electrodes to achieve the result.

Increasing the driven depth (a rule of thumb is a 40% reduction in resistance for a doubling of depth), increasing the CSA of the electrodes will assist but only marginally for every doubling of diameter.

You would normally space the electrodes at a distance greater than their driven depth.

Even so, more electrodes alone may not be satisfactory if the problem is caused by lack of soil moisture - in that case you may consider immersing the electrode/s in Bentonite. Bentonite is a clay substance which either has natural salt content, or salt added, the salt attracts and holds moisture which obviously lowers the soil resistivity - but it can dry out and shrink causing resistance to increase - you may also need to add a watering system if using this.

Another option is to use a low resistance cement that is available for this purpose, it will not deteriorate over time and doesn't require moisture replenishment, and is generally more preferred by the EPA. It also has a lower resistance/metre than Bentonite

If the soil resistance is too severe out to a large distance, then you may need to include radial traces to get the correct reading.

If your electrode is Copper or Copper plated, then avoid any fill material that has a high Carbon content as that will destroy the electrodes in a fairly short period.

If in a freeze prone environment, then you will need to get the electrodes down below the frost line to ensure satisfactory ground in winter as ice has a higher resistivity.

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#3

Re: Earth resistance

02/15/2017 3:20 AM

Now-a-days variety of chemical available. Second dig a parallel earth pit. Third is pour some salt water in to the pit.

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#4

Re: Earth Resistance

02/15/2017 11:07 AM

It basically boils down to decreasing the soil resistance and increasing the surface area between grounding rods and the soil.

Earth electrode resistance

When you find that your earth electrode resistance is not low enough, there are several ways you can improve it:

  1. Lengthen the earth electrode in the earth
  2. Use multiple rods
  3. Treat the soil

http://electrical-engineering-portal.com/improve-earth-electrode-resistance

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#5

Re: Earth Resistance

02/15/2017 12:11 PM

Have you tried pissing on it?

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#6
In reply to #5

Re: Earth Resistance

02/15/2017 12:49 PM

That's what Signal Corps soldiers do.

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#8
In reply to #6

Re: Earth Resistance

02/15/2017 3:26 PM

I thought that is what Germans did to the MG-42 after a lengthy demonstration.

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#7

Re: Earth Resistance

02/15/2017 1:47 PM

More information is needed regarding the site and what the ground it is built on consists of.

Also, where is the site as climate and other things like annual rainfall can make a difference as to which solution will work best.

Such a high resistance seems to indicate a very low moisture content ground soil or rock, and/or possibly a poor or non-compliant earth connection or joint (perhaps builder error). Have you checked these?

Is the existing earthing compliant or is it the soil that is the problem? Best to narrow it down as adding earthing pits (etc) may not help if the site earthing is not up to code.

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#9
In reply to #7

Re: Earth Resistance

02/15/2017 3:26 PM

Afterthoughts can be such a pity.

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#10
In reply to #9

Re: Earth Resistance

02/15/2017 4:10 PM

When the foundation concrete's poured it is a bit late.

If I remember correctly I think we had a similar question on CR4 previously and in the end they had to dig up the concrete to access the steel rebar to properly earth it.

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#12
In reply to #11

Re: Earth Resistance

02/15/2017 6:45 PM

Add Cavalier and bus-bar posts:

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#13
In reply to #11

Re: Earth Resistance

02/15/2017 8:57 PM

Yea, but which one had the poster digging up their foundations?

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#17
In reply to #11

Re: Earth Resistance

02/16/2017 10:37 AM

That makes this thread a duplicate.

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#14

Re: Earth Resistance

02/16/2017 4:23 AM

Tip a tanker-full of seawater onto it.

In the absence of seawater, try bovine urine.

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#15

Re: Earth Resistance

02/16/2017 9:33 AM

Might also consider a counterpoise.

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#16
In reply to #15

Re: Earth Resistance

02/16/2017 10:33 AM

As opposed to an Avoirdupois?

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#18

Re: Earth Resistance

02/16/2017 10:56 AM

Further-to Spades "GA" (Post2)

... Looking thru BSR's links, I did not come-across an old post of my own-doing...that I would have expected to be "in-the-list".

So, I did a site-search myself (for a "KeyWord"), and found it :

. . . . . . ? ... only *2* posts .... Since January "08...?

At "Corrosion Doctors.org" a good/succinct-and-to-the-point distinction is made between bentonite-based backfills and carbonaceous-type backfills.

As has been alluded-to, backfilling for earthing-type-electrodes (or instruments) is a science-unto-itself... thus, not fully understood by most (self included!).

One paper that I found quite eye-opening can still be found, here.

{...The more you know, the more you grow...}

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#19

Re: Earth Resistance

02/16/2017 11:44 AM

Motorola R-56...my grounding bible.

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#20
In reply to #19

Re: Earth Resistance

02/16/2017 12:43 PM

Welcome to the forum! GREAT resource that you reference... LOTS of expounding on every aspect, therein!

Not ONLY are the illustrations "varied-and-detailed"...

... but the VOLUMINOUS text is well thought-out and comprehensive, to say the least.

Though intended to be referencing the "structure-foundation" aspect (of installations"), the comment on pg 2-14:

"A soils engineer shall determine if the onsite excavated materials are adequate or suitable for use as backfill material. If the material is not suitable, then engineered soils shall be determined by the soils engineer" should be taken as "overall_gospel".

"Grounding electrode encasement materials (also known as backfill) shall be environmentally safe and approved by the environmental authority having jurisdiction." [See below]

4.4.1.4 GROUND PLATE ELECTRODES on Pg 4-19 reads as "Textbook" material... with Pg 4-20 adding:

"A grounding electrode encasement material should be used to backfill around the ground plate to help insure effective contact with the earth..."

and then, 4.4.1.5 CONCRETE-ENCASED ELECTRODES offers a consideration:

"Though concrete-encased electrodes (also known as Ufer electrodes, named after Herbert G. Ufer, or foundation earth electrodes) are not required by this standard, they should be used in new construction as a method of supplementing the grounding (earthing) electrode system (IEC 61024-1-2, section 3.3.5)."

"Concrete-encased electrodes (Figure 4-17) enhance the effectiveness of the grounding electrode system in two ways: the concrete absorbs and retains moisture from the surrounding soil, and the concrete provides a much larger surface area in direct contact with the surrounding soil."

Further, 4.4.1.9 GROUNDING (EARTHING) ELECTRODE ENCASEMENT MATERIALS on page 4-27 thru 4-28 "nails it", identifying the wide variety of materials available for backfilling... with the final "Shall Not" being a "Key" :

"Grounding electrode encasement material shall not have a corrosive effect on the grounding electrode system components."

What-a-biXch to go through a lot of major excavating and laying-out of a superlative grounding array ((though, I continue to wonder VIJIL, exactly *WHAT* is it for?!))... only to have "REDOX" render it useless.......................................

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#21
In reply to #20

Re: Earth Resistance

02/16/2017 1:15 PM

Thanks NDT...although I've been on CR4 for awhile...under another email/company. Luckily, I was able to keep my old CR4 name. I did a facility on Cape Cod where I went from 800+ ohm resistance to 4.95 ohm resistance. Yes, a lot of excavation, but great results.

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#22
In reply to #20

Re: Earth Resistance

02/16/2017 1:41 PM

Amen, the choir is now singing the chorus in unison. Very well done, indeed.

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#23
In reply to #22

Re: Earth Resistance

02/16/2017 3:12 PM

"Aye".... well .... we can ONLY *hope* that VIJIL can find his way back to the thread, here, and "Start-to-Begin" to...

"Help_US_help_him", by filling-in some more details.

My days of ranting about :

"poor posts"/"poorly-worded-questions"/"insufficient_info" etc. are "done".

To 'date', the sum-total of the OP's CR4 posting is this:

"we have to reduce the earth resistance to below 1 OHM. Now the reading is 18OHM. How can i optimise t below 1 Ohm?."

Perhaps he might at LEAST tell us where he is, or WHAT the purpose of his "need" is...

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#24

Re: Earth Resistance

02/18/2017 3:34 PM

If you use iron bar completely seal the feed wire connection (made twice) using a bolted clamping plate because any rust or corrosion will increase the resistance. Ideally use a copper, or copper plated steel bar with earthing clamps.

Chose a wet area of low lying ground, e.g. near a down spout, or water outlet, overflow, etc. Ensure the bottom of the bar is at least 4 feet deep in to the ground. Splay the base if possible. Back fill with a mixture of soil and moisture retaining material, such as plaster, lime, etc. known to retain dampness. Ram down the back fill well.

Avoid using any free-draining materials, stone, gravel, sand, etc. all the way up from the base of the bar. These are best used for the last six inches of infill up to the surface, ground level.

Finally shield the immediate surrounding surface area against wind and direct sunlight while allowing exposure to rain water. Good job done.

I did my own like this and no resistance could be registered on the meter. None at all.
(official electric board meter.)

Hope this helps. jt.

An archaeologist discovered a mummified body deep in the sand and which was
about 2000 years old - but it looked strangely sad and miserable?
Excited by the find they carefully unwrapped the body and found it was in fact
the most miserable looking mummy they had ever seen!
The face was strained and looked so sad; with fists clenched in rage.
Carefully prising the fingers open they saw a slip of parchment and written on it
was, 200 on Goliath to win.

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Andrew Westman (1); Bluestone (1); Brave Sir Robin (2); dj95401 (1); jack of all trades (3); James Stewart (5); jt (1); kvsubramanyam (1); ndt-tom (3); PWSlack (2); Rixter (1); SITMWY (2); spades (1)

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