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Home / Technical Articles / 3 good ways to improve earth electrode resistance

Earth electrode resistance

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

3 good ways to improve earth electrode resistance
3 good ways to improve earth electrode resistance (photo credit:
  1. Lengthen the earth electrode in the earth
  2. Use multiple rods
  3. Treat the soil

1. Effect of Rod Size

As you might suspect, driving a longer rod deeper into the earth, materially decreases its resistance. In general, doubling the rod length reduces resistance by about 40 percent. The curve of Figure 1 shows this effect. For example, note that a rod driven 2 ft down has a resistance of 88 Ω.

The same rod driven 4 ft down has a resistance of about 50 Ω. Using the 40 percent reduction rule, 88 × 0.4 = 35 Ω reduction.

By this calculation, a 4-ft deep rod would have a resistance of 88 – 35 or 53 Ω — comparing closely with the curve values.

Earth resistance decreases with depth of electrode in earth
Figure 1 – Earth resistance decreases with depth of electrode in earth

You might also think that increasing the electrode diameter would lower the resistance. It does, but only a little. For the same depth, doubling the rod’s diameter reduces the resistance only about 10 percent. Figure 2 shows this relationship.

For example, a 10-ft deep rod, 5/8 in. in diameter, has a resistance of 6.33 Ω. Increasing its diameter to 1-1/4 in. lowers the resistance o to 5.6 Ω.

For this reason, you normally only consider increasing the rod diameter if you have to drive it into hard terrain.

Diameter of a rod has little effect on its earth resistance Curve A, from Ref. 19 Curve B, average of Underwriters Laboratories tests at Chicago Curve C, average of Underwriters Laboratories tests at Pittsburgh
Figure 2 – Diameter of a rod has little effect on its earth resistance Curve A, from Ref. 19 Curve B, average of Underwriters Laboratories tests at Chicago Curve C, average of Underwriters Laboratories tests at Pittsburgh

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2. Use of Multiple Rods

Two well-spaced rods driven into the earth provide parallel paths. They are, in effect, two resistances in parallel. The rule for two resistances in parallel does not apply exactly. That is, the resultant resistance is not one-half the individual rod resistances (assuming they are of the same size and depth).

Actually, the reduction for two equal resistance rods is about 40 percent. If three rods are used, the reduction is 60 percent, if four, 66 percent (see Figure 3).

Average results obtained from multiple-rod earth electrodes
Figure 3 – Average results obtained from multiple-rod earth electrodes

Comparative resistance of multiple-rod earth electrodes. Single rod equals 100%
Figure 4 – Comparative resistance of multiple-rod earth electrodes. Single rod equals 100%

When you use multiple rods, they must be spaced apart further than the length of their immersion. There are theoretical reasons for this, but you need only refer to curves such as Figure 4 above.

For example, if you have two rods in parallel and 10-ft spacing, resistance is lowered about 40 percent. If the spacing is increased to 20 percent, reduction is about 50 percent.

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3. Treatment of the Soil

Chemical treatment of soil is a good way to improve earth electrode resistance when you cannot drive deeper ground rods because of hard underlying rock, for example. It is beyond the scope of this manual to recommend the best treatment chemicals for all situations. You have to consider the possible corrosive effect on the electrode as well as EPA and local environmental regulations.

Magnesium sulfate, copper sulfate, and ordinary rock salt are suitable non-corrosive materials. Magnesium sulfate is the least corrosive, but rock salt is cheaper and does the job if applied in a trench dug around the electrode (see Figure 5).

Trench method of soil treatment
Figure 5 – Trench method of soil treatment

It should be noted that soluble sulfates attack concrete, and should be kept away from building foundations. Another popular approach is to backfill around the electrode with a specialized conductive concrete. A number of these products, like bentonite, are available on the market.

NOTE! Chemical treatment is not a permanent way to improve your earth electrode resistance.

The chemicals are gradually washed away by rainfall and natural drainage through the soil. Depending upon the porosity of the soil and the amount of rainfall, the period for replacement varies. It may be several years before another treatment is required.

Earth electrode
Earth electrode

Chemical treatment also has the advantage of reducing the seasonable variation on resistance that results from periodical wetting and drying out of the soil. (See curves of Figure 6 below)

However, you should only consider this method when deep or multiple electrodes are not practical.

Chemical treatment of soil lessens seasonal variation of electrodes’ earth resistance
Figure 6 – Chemical treatment of soil lessens seasonal variation of electrodes’ earth resistance

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Ground rod resistance (VIDEO)

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Reference // A practical guide to earth resistance testing by Megger

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.


  1. Gra Maxa
    Oct 04, 2023

    My field of work is electrical engineering.Pls I’m glad to see your portal because it’s very educative.l personally want to call it center for knowledge and skills.

    Maxa writes
    West Africa

  2. Dinesh Kumar
    Aug 30, 2022

    Hi we are facing problem during earthing at land fill site near to a multi story building.
    We need ground resistance value 1ohm but we are getting near to 5ohm.
    We try it at multiple location but not getting success till.

    Please guide us

  3. Emmanuel Oscar Oseghale-Iyere
    Oct 06, 2021

    Good day , guys I just need more enlightenment on the grounding rod system and how to know best way to protect my appliances using Earthing system thanks I await answers.

  4. Sajid
    Sep 30, 2021

    we have a igneous rocks at site and showing 700ohm resistivity, we need 1ohm resistance please advise we reduced it up to 1

    May 23, 2021

    Kindly send me the PDF of the earthing systems… Thank you
    West Africa, Ghana

  6. Abdullah S.
    Nov 09, 2020

    Can Agricultural Magnesium sulfate be used? As I don’t see any additional compounds added to it to make it any different than chemical grade.

  7. Zakaria zaki
    Oct 09, 2020

    Can you pl send me a PDF copy of this and related articles

  8. Harischandra shinde
    Jan 19, 2020

    energy consumption of DG set with disel cost/ how to calculate

  9. Aslam
    Jan 19, 2020

    I just reading here from long time its good one can u share pdf files also for downloading

  10. Narada Maheepadma
    Dec 05, 2019

    when we install a transformer,what are the earth resistance values of transformer body and transformer neutral?what is the regulation(IEC,IEEE,..) for this?

  11. khalifa alurofi
    Oct 30, 2019

    thank you all i am so please if you could the complete information pdf
    for reducing earth resistance

  12. Eart chemical manufacture
    Aug 03, 2019

    Yes my friend say that electrolyte chemical is good for soul repair .its tructh but electrolyte shoude more good ionic charge and not leachable
    We are make many type of electrolyte and earth chemical after so many reseach and practicals
    Goldy verma 919818543288

  13. Rajendra Sawant
    Mar 24, 2018

    Can you pl send me a PDF copy of this and related articles.

  14. Stephen
    Feb 08, 2017


    Nice photo – that was from a trial site for COnductive concrete – with no requirement for an earth rod.

    The product has an estimated life span of 25 years and in soil conditions of 250 we can get reading of 1 Ohm. Check out our web site


  15. Stephen
    Jan 27, 2017

    Hi, I first notice the photo – which is me! We are testing a conductive concrete product which we use to provide an earthing solution

    Excellent Grounding Qualities
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  16. Anirban
    Dec 28, 2016

    What are the effects on resistance in plate earthing? How resistance varies with surface area of the plate?

  17. Evans Armah
    Dec 03, 2016

    Thanks for this post, very useful. Please can I connect main earthing of a 500KVA transformer to the neutral terminal. The main earth electrode resistance is 0.5ohms.
    Thank you

  18. Sergio
    Nov 29, 2016

    Well Done, very interesting and practical article!

  19. andrew
    Nov 28, 2016

    strange in the UK you can purchase an earth inspection and test box and the supplier also supplies a conductive mineral fill for high resistance soils but this needs the rod to be buried in a pit like a fence post hole to the same depth as the rod. One other thing missing is using higher gauge wire like 10 mm .square

  20. Aung Moe Moe
    Nov 27, 2016

    How about earth plate? Can you explain me? How about mountain side how to do earthing and can made earth lake or not?

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