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.
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.”
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.
Reference: Fluke Earth Ground Testing Fact – Distributor Training Program
SANS10142-1 WIRING REGULATIONS CONTAINS THE PRINCIPLES TO BE FOLLOWED FOR THE WIRING OF PREMISES.
No one reads the questions so why ask
What is earth fault ?
i got a reading of 5.81 ohms on a changeover switch gear earth point while the generator (350KVA) earth point gave a reading of 1,89 ohmns, is it safe?
Dear Sir,
My enquiry is what is the value expected amp/ohm on Ground Pipeline ?
I just performed a Ground Protection between Pipeline & offshore structure what tie in to the Sea Bed Anode ground is Cadweld on Pipeline which is coming from Offshore 30 inch Pipeline going onshore due to allow welding activities while the Pipeline is in-service liquids onto is Crude.
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Question what is the amp value ?
Thanks
Dear
You Mentioned In the article
NEC 50.56 Actually It Shall Be NEC 250.56
thanks
I don’t see 50.56 in the NEC. I don’t see a 250.56 either, what year of the NEC you are using, please advise. Thank you.
My question is that what should the value of earthing of residential boarding school hostels and a classroom for all commercial buildings. kindly give your valuable answer so that we can maintain our earthing pits as per given your suggestion.
I need to learn
What should be ground ohms for 10kva solar powered system?
Hi
that very good
But I have reach to less than 1 ohm of earth resistance by my special way
Hi
can any one tell us the IEC standard for earthing resistance value in general in Oil fields please.
thanks
Seeking your support, appreciate if you could share to me MV Protection coordination study sample.
Sir what is the correct value for earth trasformer
There is no NEC 50.56.
NEC 250.56 11th edition stated 25 ohms and less.
NEC 250.56 is excluded from 12th edition
In my company, a telecommunication giant in Nigeria, the standard earth resistance value ranges from 2.0 Ohms and below.
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
Very Educative … Thanks Edvac …!
is there any reference about the resistance value between clean and dirty earths.
Nice one, very educative, can i get a earth resistance tester and at how much
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
Very good
Hi, meter reads o.23 Ohms, is this good or bad?
yes very good
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
Because inverter has an isolation transformer and surge circuit inside to avoid cascading the fault current goes.to other appliances
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
Like to buy Tong earth tester like in the photo please get back to me.
Would like to buy an earth tester (ideal ground resistance meter)
Sir sgp course available ?
So what is the correct value for earth?
As per standard
Different application different ohm required
from less than 0.5 ohm to 25 ohm as per application ,soil and standards, approximatly
What should be size of lighting arrester pitch
Please I want to do earthing as my thesis for my 2nd degree project so can you give me some PDF on earthing?
contact me on this email i will send u PDF
What damage can lake of earth cause to sound proof generator
This is great keep on
Dear Edvard,
Can you please send me if possible the complete IEC standard in WORD or PDF file.
Thanks and Best Regards.
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
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.
Thanks A lot
REALLY, BELLOW 25 OHMS IS ACCEPTABLE (NEC 250-56)
very informative , thanks Edvard.
All articles are very helpful Edvard
Congrats and Thanks a lot
You guys are doing a great job! Very educative. This is electrical engineering made easy and real. keep it up. Thank you.
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
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?
Babar: In rocky areas I find the best grounding electrodes to be chemical ground rods. If the subsurface ground is solid rock, you would need to bore a hole or cavity into the rock, place the chemical rod into the hole and backfill the hole with “ground enhancement materials. Initially, the ground impedance may test higher than your target impedance but it will fall as the Rod’s internal salts dissolve and form “electrolytic roots” and attach to the undisturbed rock. A good chemical rod vendor would be ERICO.
Additionally, grounding systems should be designed to “maintain a low impedance on a seasonal basis” instead of initially as installed. Seasonal moisture levels change especially in Clay soils.
Thanks Edvard
I have a megger earth clamp-on meter, how will I sue it to measure earth resistance value as opposed to conventional earth tester?
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.
i will like to know how can one can increase the resistance of his earth system as years runs by.
I m in biomedical field.what must be normal,earth resistance for biomedical equipments.ex for anesthesia workstation.
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?
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?
Good enough. Thanks Edvard
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?
You may Rap around the ground cable to water pipe. it will reduce the grounding resistance.
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 .
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 )???
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.
In my experience we could achieve close to zero that if all the earth rod are interconnected
whats the domestic,human,and industrial value of grounging
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.
Hi i want to know the recommended earth resistance value for electrical installation
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”.
so ….we cannot find earth resistance practically
We can find earth resistance practically. Earth resistance tester with 3 points or a clamp on type meter will help. Its easy to operate.
What it’s the purpose of earth megger
straight answer to my question. most useful site. Thanq
You’re welcome Suresh! Straight to the point!
Very nice shorted ( concetrated information) ….I hope to see more like that ….. thank
Thank you Emad!
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?
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,
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…
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
Thanks Ashraf!
RAS
describe 4 point earth resistance measurement method,
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.
In house we get 7 to 5 ohms.
my think bildup
Nice information about earthing resistance….
where i can informasi accurate troubleshooting electrical,i m from indonesia,write english no good
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.