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Home / Technical Articles / What Is a Good Ground Resistance Value?

Zero Ohms… Not Really!

The goal in ground resistance is to achieve the lowest ground resistance value possible, that makes sense economically and physically, when contacting the earth, also known as the soil/ground rod interface.

What Is a Good Ground Resistance Value?
What Is a Good Ground Resistance Value?

Ideally, a ground should be zero ohms of resistance, but…

Unfortunately, there is not one standard ground resistance threshold recognized by all certifying agencies.

The NFPA and IEEE recommend a ground resistance value of 5 ohms or less while the NEC has stated to “Make sure that system impedance to ground is less than 5 ohms specified in NEC 50.56. In facilities with sensitive equipment it should be 5ohms or less.

Copper Earth Rod thermoweld connection at a 33kV Substation in Nakheel, UAE
Copper Earth Rod thermoweld connection at a 33kV Substation in Nakheel, UAE (photo by Muhammad Adnan; Substation Designer via Flickr)

The telecommunications industry has often used 5 ohms or less as their value for grounding and bonding while electric utilities construct their ground systems so that the resistance at a large station will be no more than a few tenths of one ohm.

In general, the lower the ground resistance, the safer the system is considered to be.

Reference: Fluke Earth Ground Testing Fact – Distributor Training Program

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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.

76 Comments


  1. reza
    Aug 21, 2020

    Hi
    that very good
    But I have reach to less than 1 ohm of earth resistance by my special way


  2. Mohammad H. Hamdi
    Jul 22, 2020

    Hi
    can any one tell us the IEC standard for earthing resistance value in general in Oil fields please.

    thanks


  3. Carlos C. Tamayo Jr.
    Jun 25, 2020

    Seeking your support, appreciate if you could share to me MV Protection coordination study sample.


  4. Garba musa
    Jun 19, 2020

    Sir what is the correct value for earth trasformer


  5. Muhammad Shaheryar
    Apr 06, 2020

    There is no NEC 50.56.
    NEC 250.56 11th edition stated 25 ohms and less.
    NEC 250.56 is excluded from 12th edition


  6. Emeka Chime
    Feb 24, 2020

    In my company, a telecommunication giant in Nigeria, the standard earth resistance value ranges from 2.0 Ohms and below.


    • andy chan
      Feb 27, 2020

      Dear Emeka Chime,

      Please let me know, the standard earth resistance value ranges from 2.0 Ohms, the 2.0 ohms is quote from what authority or international standard?

      Thanks so much


  7. SOJI
    Jan 15, 2020

    Very Educative … Thanks Edvac …!


  8. Ali
    Dec 31, 2019

    is there any reference about the resistance value between clean and dirty earths.


  9. Kimetu
    Dec 07, 2019

    Nice one, very educative, can i get a earth resistance tester and at how much


  10. Satti
    Nov 28, 2019

    I have checked the earth resistance and it’s result is point zero one six seven so kindly tell me about the earth, that is good or not
    Result= .0167


    • Faisal Mohamed
      Oct 23, 2020

      Very good


  11. Eng. Seth Wilson
    Nov 04, 2019

    Hi, meter reads o.23 Ohms, is this good or bad?


    • MOHAMED MOUSTAFA
      Jul 05, 2020

      yes very good


  12. Ugama Albert
    Oct 18, 2019

    I installed a 5kva inverter in a house that has a thunder arrester and it’s earted. But the inverter was still destroyed by thunder. This made me to to run a test on the earthing and was discovered it was 27ohms. How come it was only the inverter that was affected and not the house appliances as well


    • LalitKishor
      Nov 04, 2019

      Because inverter has an isolation transformer and surge circuit inside to avoid cascading the fault current goes.to other appliances


  13. Mahesh
    Oct 04, 2019

    Earthing for Any equipments is Design always request customer for Soil ERT Reports and Design for Equipments or any Kind of Grid.
    Earth Enhance Compound Role is bigger than Metal Part becuse we use Metal to consider Falut Current and Life for Metal but without Good and Quality Compound its not possible.
    Avoid to use any mineral who can Damager or Corrosion your Metal Later .
    India Follow IEC as well IEEE .using CDEGS Software for Desiging Earthing and Lightning
    We has to mentioned Latest Tech Documents is our inquiry or Tender
    M-91-9910398999


  14. Mr G. T Apera
    Sep 04, 2019

    Like to buy Tong earth tester like in the photo please get back to me.


    • Mr G. Apera.
      Sep 02, 2020

      Would like to buy an earth tester (ideal ground resistance meter)


  15. Prashant shalikram pustode
    Aug 24, 2019

    Sir sgp course available ?


  16. Wisdom Ayensu
    Aug 12, 2019

    So what is the correct value for earth?


    • Arif khan
      Apr 20, 2020

      As per standard
      Different application different ohm required


    • MOHAMED MOUSTAFA
      Jul 05, 2020

      from less than 0.5 ohm to 25 ohm as per application ,soil and standards, approximatly


  17. Kafui Sampene
    Jul 31, 2019

    What should be size of lighting arrester pitch


  18. Emmanuel Ephraim Yalley
    Jul 14, 2019

    Please I want to do earthing as my thesis for my 2nd degree project so can you give me some PDF on earthing?


    • zakir hussain
      Oct 09, 2019

      contact me on this email i will send u PDF


  19. Lucky friday
    May 30, 2019

    What damage can lake of earth cause to sound proof generator


  20. Lucky friday
    May 30, 2019

    This is great keep on


  21. Eladio Mosqueda
    Mar 09, 2019

    Dear Edvard,

    Can you please send me if possible the complete IEC standard in WORD or PDF file.

    Thanks and Best Regards.


    • EKIA BONNY
      Aug 11, 2020

      Is there specific ratio for earthing materials like NaCl,charcoal dust etc when it come to residential and industrial earthing?
      I need your help please.
      Thanks


  22. Dr. Md Abdus Salam
    Feb 20, 2019

    The highly recommended value of ground resistance for a residential and commercial area is less than or equal to 1 ohm. You need to use more earth electrode to achieve this value.


  23. Mahmoud Awad
    Jan 05, 2019

    Thanks A lot


  24. JOSE CAMPOS
    Dec 24, 2018

    REALLY, BELLOW 25 OHMS IS ACCEPTABLE (NEC 250-56)


  25. Daham Noaime
    Oct 20, 2018

    very informative , thanks Edvard.


  26. Jorge Chávez
    Aug 07, 2018

    All articles are very helpful Edvard
    Congrats and Thanks a lot


  27. Ojiyovwi Michael
    Aug 02, 2018

    You guys are doing a great job! Very educative. This is electrical engineering made easy and real. keep it up. Thank you.


  28. samer khatib
    Jan 25, 2018

    good day
    can I connect aluminuim wire to the earthing copper rods , i mean are there any problem to make these connection in the present time or in the future .
    i appreciate your reply


  29. Babar
    Nov 22, 2017

    Hey man thats a brief and very informative article.
    i was doing testing in my area, in rocky areas, my lightening resistance was above 300 ohms with 10feet deep cooper plates, where as in other portions it was well below 25ohms, i even hit 5ohm also.
    So we are basically measuring “Potential of Lightening Fall” of a ground. Lower the resistance, higher will be possibility of lightening isnt it?


  30. Eddy Kasim
    Nov 16, 2017

    Thanks Edvard


  31. solomon
    Jun 19, 2017

    I have a megger earth clamp-on meter, how will I sue it to measure earth resistance value as opposed to conventional earth tester?


  32. Sanele
    Mar 28, 2017

    I am working in substations, I like to know how many ohms should I get when doing earth resistance in the whole substation? Your assistance will be much appreciated. Thank you.


  33. weyih franklin
    Mar 09, 2017

    i will like to know how can one can increase the resistance of his earth system as years runs by.


  34. Aniruddha Moholkar
    Mar 07, 2017

    I m in biomedical field.what must be normal,earth resistance for biomedical equipments.ex for anesthesia workstation.


  35. prakash deo
    Jan 17, 2017

    I am working in Dinshaws Ice cream Nagpur. We have bakery also, I would like to know that what is the value of earthing in Ohms in the earthing points?


  36. ananth
    Jan 02, 2017

    Have you do any earthing tests related to 11 KV motors?

    I have to do earthing tyests with 11 KV motors,

    can you please give some ideas?

    and documents related that?


  37. Tunji
    Nov 25, 2016

    Good enough. Thanks Edvard


  38. trisha gupta
    Aug 22, 2016

    How to measure the value of earth resistance in Multi-Dwelling Unit(Apartments) where neither the earth pit is not accessible, nor the earthing rod?

    Are there any non destructive methods available? By non destructive, I mean without digging?


    • Imran Malik
      Oct 25, 2016

      You may Rap around the ground cable to water pipe. it will reduce the grounding resistance.


  39. suzzanae
    Jun 22, 2016

    Hi, I would like to know whether we can achieve 5 ohm for more than 10 years or not.
    And, can we suggest type of earthing just differentiating wet soil, sand soil or rocky soil without calculation. if any standard thumb rule are there please share .

    Also. LPS for metallic tower and not metallic tower .


  40. gilbert
    May 14, 2016

    may i ask some question reguardimg on bonding of grounding,? how come that it is more efficient my grounding system if i’m goin g to bond the grounding of my lightning arrester in a building grounding? if a high voltgage and current occur cause by a lightning,. do i have a current pass through my equipments which is grounded (connected to a building grounding )???


  41. Jimmy Jones
    Dec 11, 2015

    If I turn off all breakers in my homes main breaker panel and remove the main Neutral Wire from the panel tie point, then run a wire from one unused 120 volt 20 amp breaker to ground the breaker should clear if the ground is sufficient. Right? If it doesn’t clear, then the ground must be over 5 or 6 ohms. I know this is dangerous and I’m not recommending anyone doing it but am I correct in what I’m saying here? I’ve seen people try to obtain this 5 ohms or less ground and never come close to obtaining a low enough resistance reading by itself to clear the breaker.


  42. v.ragu
    Dec 11, 2015

    In my experience we could achieve close to zero that if all the earth rod are interconnected


  43. muhammad salam
    Oct 16, 2015

    whats the domestic,human,and industrial value of grounging


  44. Salman Kamal
    Oct 13, 2015

    Although zero ohm is the most ideal figure, but it is not always the case, in my experience along, there are many solution to make nearby zero, such as carbon and salt arrangement with many earth copper rods connected together and surrounding the premises such as substation. The worst case where you have Stoney ground area with a lack of humidity or source of water.


  45. MIUNSHYA MUSONDA
    Sep 04, 2015

    Hi i want to know the recommended earth resistance value for electrical installation


  46. diolan
    Aug 31, 2015

    hello edvard, the article of the nec is the 250.56 and the value shall be less than 25 ohms. In the article is missin the number “2”.


  47. surya
    May 03, 2015

    so ….we cannot find earth resistance practically


    • Girish R Pillai
      Feb 22, 2016

      We can find earth resistance practically. Earth resistance tester with 3 points or a clamp on type meter will help. Its easy to operate.


  48. joseph
    Apr 21, 2015

    What it’s the purpose of earth megger


  49. Suresh
    Jan 02, 2015

    straight answer to my question. most useful site. Thanq

    • Edvard
      Edvard
      Jan 03, 2015

      You’re welcome Suresh! Straight to the point!


  50. emad hassoun
    Oct 15, 2014

    Very nice shorted ( concetrated information) ….I hope to see more like that ….. thank


  51. godwin
    Oct 15, 2014

    I really like a site like this, were I can reffer some of my engineering questions to. I would like to know how to test a lightning arrestor that is mounted on a mast with a copper tape running down to earth pit?


  52. ghulamsarwar
    Aug 03, 2014

    well this z vry good site for electrical information,,,,v r getting a vry low resistance with copper groundind rod almost 1 ohm……& less than 5 ohm with galvanized steel rod of 19mm dia with 24mm lenght,


  53. Vivek
    Jun 06, 2014

    I have been searching a site like this for quite a long time. I’ve finally discovered the site for all my electrical references. I feel really happy for the good work you do, Edvard. Thanks a lot…


  54. ashraf
    Jun 06, 2014

    Dear Edvard.
    That is so good information , you are professional and I would like to keep in touch with you.
    Thanks
    Sincerely.
    Engineer.
    Bush. Ashraf


  55. ouadi
    May 26, 2014

    RAS


  56. shrikant
    May 10, 2014

    describe 4 point earth resistance measurement method,


    • Girish R Pillai
      Feb 22, 2016

      Its very easy and explained on the meter itself in simple language. To arrange the spikes in a straight line at measured intervals. Apply current by pressing the push button. Note the reading and calculate based on the formula which is inversely proportional to the distance between spikes.


  57. Raj
    Apr 24, 2014

    In house we get 7 to 5 ohms.


  58. ashish
    Feb 02, 2014

    my think bildup


  59. Sohail Khan
    Dec 29, 2013

    Nice information about earthing resistance….


  60. iwak
    Dec 25, 2013

    where i can informasi accurate troubleshooting electrical,i m from indonesia,write english no good


    • jaweed
      Aug 03, 2019

      dear sir,
      Good morning ,we use CA-6417 Ground Test Meter,during testing meter display showing LOOP(blinking) & 0.23 Ohm,my Question is what the meaning LOOP,
      please explain grounding is or bad.if ground is tell me solution your reply highly appreciated.

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