## 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.

*,*

**the lower the ground resistance***is considered to be.*

**the safer the system****Reference:** Fluke Earth Ground Testing Fact – Distributor Training Program

Eladio Mosqueda

Dear Edvard,

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

Thanks and Best Regards.

Dr. Md Abdus Salam

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.

Mahmoud Awad

Thanks A lot

JOSE CAMPOS

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

Daham Noaime

very informative , thanks Edvard.

Jorge Chávez

All articles are very helpful Edvard

Congrats and Thanks a lot

Ojiyovwi Michael

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

samer khatib

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

Babar

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?

Eddy Kasim

Thanks Edvard

solomon

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

Sanele

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.

weyih franklin

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

Aniruddha Moholkar

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

prakash deo

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?

ananth

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?

Tunji

Good enough. Thanks Edvard

trisha gupta

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

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

suzzanae

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 .

gilbert

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 )???

Jimmy Jones

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.

v.ragu

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

muhammad salam

whats the domestic,human,and industrial value of grounging

Salman Kamal

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.

MIUNSHYA MUSONDA

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

diolan

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”.

surya

so ….we cannot find earth resistance practically

Girish R Pillai

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

joseph

What it’s the purpose of earth megger

Suresh

straight answer to my question. most useful site. Thanq

Edvard

You’re welcome Suresh! Straight to the point!

emad hassoun

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

Edvard

Thank you Emad!

godwin

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?

ghulamsarwar

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,

Vivek

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…

ashraf

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

Edvard

Thanks Ashraf!

ouadi

RAS

shrikant

describe 4 point earth resistance measurement method,

Girish R Pillai

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.

Raj

In house we get 7 to 5 ohms.

ashish

my think bildup

Sohail Khan

Nice information about earthing resistance….

iwak

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