Testing of earth /ground copper rod

[bbabythai]

A month or so ago our electricians did all the wiring at our building. They put in a grounding rod (copper). I previously raised a thread about this. 

 

I decided to ask them to test it today. Photos below. The reading was 147. 

 

As a comparison, they stuck a metal rod into the soil next to it and attached the same testing equipment. The reading came back at 533. This metal rod was not attached to any wiring or anything. They just stuck it in the soil and attached that device. 

 

They said that the reading of 147 proves that the grounding rod is ok. Do you agree? I have absolutely no knowledge about this and appreciate any comments

tahnks

 

[stouricks]

There has got to be TWO places the probes are placed to get a potential difference of anything. So what was the 1.47 or 5.3 volts between?

The sparky needs to calibrate his volt meter.

Edited September 5, 2020 by stouricks

[bbabythai]

1 hour ago, stouricks said:

There has got to be TWO places the probes are placed to get a potential difference of anything. So what was the 1.47 or 5.3 volts between?

The sparky needs to calibrate his volt meter.

Hi. Its my fault as I dont understand your comment. I have limited knowledge and thus wanted to know if you could be more specific. He placed the reader on the earth rod and showed the reading. Then he placed it on the rod in the soil that he put there for the test and it had the higher reading. What is wrong with this?

[simon43]

From your meter photo, I can see that they are measuring resistance, and measure a resistance of 1.47 ohms between the earth rod connection and ??? (I don't know where the other probe is connected, because it's not in your photo).  In order for the earth rod to be effective, there should be a low resistance between your earth connection in the house and the soil.  The measurement of 1.47 ohms seems to suggest that there is a low resistance path, although I have no idea what points their comparison measurement was made...

 

One thing to check:  Earth rods should be made of solid copper metal, because that is a very good conductor of electricity.  I've found 'copper' earth rods made of steel and painted brown!  So take a sharp knife and see if you can scrape off the brown colour on your earth rod ????

[sometimewoodworker]

7 minutes ago, simon43 said:

Earth rods should be made of solid copper metal,

No they should not. They should be made of copper coated steel. Just try to hammer a copper rod into most soil around here and you will find it bends very easily and won’t go in deep enough.

[RichCor]

YouTube  How it's done, and Why it's done

 

External Earth Fault Loop Impedance on a TN-C-S Earthing Arrangement Measuring Ze in Ohms (max 0.35)

 

 

 

Earth Fault Loop Impedance Test & Prospective Fault Current Test

 

 

[bbabythai]

39 minutes ago, sometimewoodworker said:

No they should not. They should be made of copper coated steel. Just try to hammer a copper rod into most soil around here and you will find it bends very easily and won’t go in deep enough.

A month ago I watched the guy bang the long copper rod into the soil. He hit it hard with a hammer. It certainly did not bend

[sometimewoodworker]

12 minutes ago, bbabythai said:

A month ago I watched the guy bang the long copper rod into the soil. He hit it hard with a hammer. It certainly did not bend

And you are absolutely sure it wasn’t copper bonded steel? You would not be able to see the difference.

[Metropolitian]

The right way of measuring the earth/ground is in two steps.

 

First is measuring the ground rod ;

The meter has 3 connections, E P and C.

The E probe on the electrode (ground rod that's hammered into the ground for your installation)

and the P connection to an probe at 10 meter from the electrode/rod

and the C connection probe in the ground 20 meters from the electrode/rod.

 

Second step is either measuring between the ground rod and the earth/(incoming neutral) busbar in the CU as two point measuring

OR

leave the two probes in the ground and move the E probe to the CU and compare with the first test.

 

All data given, results should not exceed the 5 Ohms.

[RichCor]

2 hours ago, bbabythai said:

I decided to ask them to test it today. Photos below. The reading was 147. 

 

As a comparison, they stuck a metal rod into the soil next to it and attached the same testing equipment. The reading came back at 533. This metal rod was not attached to any wiring or anything. They just stuck it in the soil and attached that device. 

Very odd testing descriptions.

 

Additional suggestion on what should be measured and what those measurements should be and mean, a 2018 ThaiVisa thread referenced a expectation lookup table for ground soil types

 

Earth Electrode Testing (link)
By longball53098, December 12, 2018 in The Electrical Forum

 

User Stud858 recommended looking at TABLE 1 

Table 1 provides various ground resistances which can be used as a rule of thumb.

 

 

...Also recommend viewing pinned ThaiVisa threads

 

How to check your earthing system
By Forkinhades, January 5, 2014 in The Electrical Forum

  

 

[Yellowtail]

In 12 years moving carnival rides I've pounded in hundreds or perhaps thousands of ground rods, they were most all copper-clad steel.  

[wayne07836]

The Ground Rod test being performed here is called a Fall of Potential Method (there is another method using a clamp on meter but this is the preferred method) and to carry this out correctly the Ground Rod must first be disconnected from the electrical service so that you get an accurate reading of the rod that is not influenced by any parallel paths.

Generally ground Rods are copper coated steel and not pure copper as they would be expensive, offer only negligible lower resistance and not be strong enough to be driven into the ground as was pointed out by another poster.

The test is performed by connecting to the ground rod and 2 further stakes placed in the soil about 20 meters apart.

To ascertain if your results have passed the test you need to establish what type of earthing system you have (typically in Thailand a TT 2 wire system) and the means of short circuit and ground fault protection you have on the incoming supply.

It is safe to say that using a ground rod on its own as a sole means of earth would not give you a value low enough (ZE External Earth Fault Loop Impedance) for standard circuit breakers to trip fast enough to meet governing standards, this value would need to be 0.2 Ohms or lower for a TT system.

The way that conformity is met is to introduce additional protection by use of an RCD (Residual Circuit Devise) of a minimum of 100ma for the whole electrical system with a further reduction to 30ma for socket outlet circuits.

With a 100ma RDC main switch your ground rod value can be as high as 500 Ohms and with a 30ma RCD it can be as high as 1667 Ohms.

 

So the conclusion for the safe use of Earth Rods or Ground Rods is to add additional protection with the use of an RCD and it will most certainly pass, it would be very unlikely to give you a value higher than the requirements.    

 

https://www.fluke.com/en/learn/blog/grounding/earth-ground-fall-potential  

[Yellowtail]

2 minutes ago, wayne07836 said:

 

The test is performed by connecting to the ground rod and 2 further stakes placed in the soil about 20 meters apart...

 

Is this correct?

[AAArdvark]

This would essentially measure the resistance of the earth between the two rods. If the measurement is high it would mean there is a probable issue with the earth composition between the two.  Measuring between the new rod and the other test rod should be very close to the first test rod and if not, test between the two test rods.

Edited September 6, 2020 by AAArdvark

[The Theory]

19 hours ago, bbabythai said:

the grounding rod is ok. Do you agree?

Just get a voltmeter and check the voltage between the load (hot) and the Ground, if it shows very close voltage to the house voltage (between Hot and Neutral) then it would be ok. 

[mikecha]

if u go to google and look fluke meter nr 1621

if u read through there is a diagram showing you how to do  and the readings hope thi explains better

 

it shows the 3 wires 1 to the earth pin 2 to probes  different distances 

 

sucess 

[sometimewoodworker]

1 hour ago, Yellowtail said:

1 hour ago, wayne07836 said:

 

The test is performed by connecting to the ground rod and 2 further stakes placed in the soil about 20 meters apart...

 

Is this correct?

Yes

 

[Dazinoz]

Who says that the second or third rod driven in for testing has a good earth? It/they could have a poor connection too.

 

Earth testing instrument as shown in some posts may not be available.

 

As someone else stated measure the voltage at an outlet (between active and neutural) then between active and earth if they are the same then the rod has good connection. The lower the voltage reading then the higher the resistance of the rod.

[natway09]

If you bang a grounding rod into the soil just about anywhere in Thailans 5 feet it will do the job.

Very limestone or pumice soils may require a further depth

[xtrnuno41]

First, you say 147, but it is 1.47 ohms. Second 533 ohms, or 5.33 ohms? That would be very good, however did they test right.

 

I see 3 wires on the meter, so they did a 3 point testing? But you said they just put 1 point close to the rod. Where was the other one?

Or they just did a 2 point testing and left the third one out? Not connected? Then they should have switched the meter to 2 point measuring.

But should have placed the probe way further.

 

With a 3 point there should be 2 additional probes. There are 2 more, beside the ground rod, of them somewhere and should be 10 times the length of the rod placed further in the field. At least one of them and the other probe on half the distance.

Then they should do the test about 2 times more by moving the "half way" probe, to see if the readings are consisted.

 

I dont know how serious the electricians are, as they have an expensive Fluke. However if they arent serious in doing their job or dont know how

then this measuring is BS. Not being serious can also mean they trick you in easy way, as they know how to get low reading and you believe it.

You arent educated in it, so they can tell you anything, you rely on them.

It is the same as you go to garage for a flat tire and they say your engine broke down.

 I couldnt tell now if all is right.

Measuring also depends on what  time you perform it. Did you do it right after a splashing rain or in summer when its dry?

Best to do it of course in ...summertime.

 

 

 

[The Theory]

Hammer the rod where the ground always get wet either by rain or garden water.  
I hammered one in the garden only for fences and some metal roof we have. The metal roof has no trusted ground in case of lightning. The rod make it easy (connected to the metal sheet roof and fences by a AWG 4 copper) not jumping to unwanted objects. 
 

 

 

Edited September 6, 2020 by The Theory

[alacrity]

The instrument connection isn't made to the ground rod. It's connected to the cable side of the connection (supposed to be a crimp) to the rod. Looking at the photo, the connection is a cluster____ of lead and tin. The gravel would be more conductive on a rainy day.

Get yourself a competent electrician.

 

[brianthainess]

I know im changing the subject somewhat, but can anyone explain to me why ; when there is a big lightning flash over my house why does the RCD flip off ?

[bankruatsteve]

25 minutes ago, brianthainess said:

I know im changing the subject somewhat, but can anyone explain to me why ; when there is a big lightning flash over my house why does the RCD flip off ?

Lightning produces EMF which can put voltage spikes and induce current on anything conductive.  These are not necessarily equal (on the L and N) and can trip RCD.

[Crossy]

12 hours ago, alacrity said:

The instrument connection isn't made to the ground rod. It's connected to the cable side of the connection (supposed to be a crimp) to the rod. Looking at the photo, the connection is a cluster____ of lead and tin. The gravel would be more conductive on a rainy day.

Get yourself a competent electrician.

 

It's actually a rather crumby looking but probably perfectly sound thermite weld which is the approved method to attach the cable to the rod.

 

[maxpower]

23 hours ago, Dazinoz said:

As someone else stated measure the voltage at an outlet (between active and neutural) then between active and earth if they are the same then the rod has good connection. The lower the voltage reading then the higher the resistance of the rod.

Multi-meters are high impedance so if there was a million ohms at a corroded earth rod connection your meter would likely read full the line voltage minus a few milivolts. There is also the risk of reading leakage from other appliances if a ground line was floating.

 

A dirty dangerous way to test earth connection would be to measure the voltage drop across a load connected between line and earth rod .