Earth Electrode Testing

[longball53098]

Earth Electrode Testing

Ok here is my question for the day/week. 

A friend just bought a Earth Resistance tester from Hardware House. A  UNI-T model UT-521. We have been discussing earth testers and socket testers for quite some time. I explained to him and showed him the socket tester I have that includes earth loop tests and an RCD test. I have this tester: http://www.dyinstrument.com/duoyi/?q=socket_polarity_loop_tester/DY207A

 

I have checked all my sockets at home here in Rayong and all test good for correct polarity and earth. The exception is when the tester finished up with the Loop test it does not show green but Flashing Yellow. According to the manual this indicates a loop resistance higher than 1.8 oms but less than 92 ohms with the caveat that the earth path needs checking and the installation needs checking. Had this test been Red that would indicate above 93 ohms and Danger check installation now. This testing has been done several times over the last 2 years. I have been deciding to buy a earth resistance tester since then so now this friend has one so time for a test with this new tester.

 

My system is 3 phase with a Schneider breaker panel. 4 wire 3 phase with neutral. No MEN link installed as this was installed 10 years ago and my Sparkie would not could not validate a MEN system in our mooban so I told him do not connect it. The incomers from meter are NYY 16sqmm 4 conductor cable about 45 meters from meter. Overhead for 15 meters and then underground in HDPE pipe to the house and panel.

 

A couple days ago I took the tester out to the yard and opened the access to my earth rod. Connected the tester to the rod, and the two probes per the manual. My rod is 2.4 meters deep. I performed 2 tests. First test with probes at 5 meters and 10 meters distant from the rod. Second test was with probes at 10 meters and 20 meters. When making the tests both returned an ohm value of 34.7 ohms. This makes me nervous as everything I read and understand this value should be down near 5 ohms or less. 

The other question I have regards the setup for testing. When I made these 2 tests the 10sqmm cable from my breaker panel was still connected to the rod. Should I have removed the earth cable from the panel before making the test? I cannot find any real answer to this or I am missing it somewhere.

 

So the question to the experts is? Am I performing the test correctly and if the 34.7 is accurate what do I do next to lower that? Or what am I doing wrong?  Am I doing this safely?

 

Thanks for any help

[Crossy]

Seems reasonable for a single rod, obviously the lower the better. Do you have RCD/RCBOs on "risky" circuits?

 

You should remove any connections to the rod before testing but it's not likely to make a vast difference since you don't have MEN.

 

 

 

[stud858]

http://www.ee.co.za/article/principles-testing-methods-earth-ground-resistance.html#.XBDjv2lxXqB

This will be helpful I think. Or bore you to death.

[longball53098]

20 minutes ago, Crossy said:

Seems reasonable for a single rod, obviously the lower the better. Do you have RCD/RCBOs on "risky" circuits?

 

You should remove any connections to the rod before testing but it's not likely to make a vast difference since you don't have MEN.

 

 

 

Yes on the RCDs. No breaker style but the single socket type from Safety Cut Company. Actually 5 or 6 of them in primary places

[Crossy]

20 minutes ago, stud858 said:

http://www.ee.co.za/article/principles-testing-methods-earth-ground-resistance.html#.XBDjv2lxXqB

This will be helpful I think. Or bore you to death.

Thanks for that and Table-1 seems to support what our OP is seeing on his 2.4m rod.

 

@longball53098 if you can validate the presence of MEN on your supply (look for a neutral earthing rod on every 3rd or so pole) then adding a MEN link will improve your overall safety somewhat.

[stud858]

How does your earth rod look?

Corroded,  quality conductor? Or any old alloy length found on the side of the road was driven down? 

Wouldn't hurt to tie.in a second rod for piece of mind. 

 

 

[sometimewoodworker]

Is the earth around your rod damp or bone dry, that could also have an effect.

[Crossy]

9 hours ago, sometimewoodworker said:

Is the earth around your rod damp or bone dry, that could also have an effect.

Yeah, the document linked to by stud858 supports this. Soil resistivity from 30Ωm (swamp) to 1000Ωm (dry gravel) or even 30,000Ωm (stony soil).

 

In very difficult situations specialist techniques have been developed, Google "Ufer ground" which developed into the concrete encased electrode now widely implemented in the US.

 

[longball53098]

13 hours ago, stud858 said:

How does your earth rod look?

Corroded,  quality conductor? Or any old alloy length found on the side of the road was driven down? 

Wouldn't hurt to tie.in a second rod for piece of mind. 

 

 

Actually back a couple years ago when Crossy was reporting on his rod being corroded and it disappeared I decided to have my guy drive a second rod down right next to the original. Both were clamped together at the top and the cable connected. So I added a second 5/8 inch rod made of copper coated steel same as the first. 2.4 meters long. The surrounding earth is damp quite often as my wife waters the garden in that area frequently. Definitely not hard and dry at the surface anyway and the rod drove in easy as I recall so must be OK. When the house foundation was dug down in the area the ground down 2 meters was sandy, stony soil and in January no water down that deep at all. Ground water in this area is about 10 meters or more down as most hand dug wells are  15 to 20 rings for good supply of water.

[Daffy D]

My ground rod is near our septic tank which is made from those concrete rings so obviously always damp. 

 

Been years since installation so don't know if there is actually any rod left in the ground, must check that sometime.????

 

I think crossy once suggested testing the earth connection by putting a low wattage bulb between the Live and the Earth and it should light up.

 

I did try that once but the Safe-T-Cut tripped so gave up on that at the time ????

 

Added to my long to-do list   

[Wirejerker]

The DY207A is giving the correct information and for your setup it shows your earth rod is in the range of 1.8 to 92 ohms. ( it will be in the upper closer to 92 ). Earth loop impedance is the resistance from your live conductor back to and through the tranny where it is earthed on the neutral side then back to your earth. You have elected to use the ground as your return path hence the high reading. An earth fault under these conditions will not trip a normal Circuit Breaker so you must have everything protected by RCDs or RCBOs. To get the earth impedance down you need to connect the MEN link. You are wasting your time doing those tests with stakes at different distances as that is usually only done at the tranny end. If your earth rod looks Okay and is firm in the ground it should be fine and the reading from the 207A shows that it is. If your still not happy bang another rod in and connect to that. Don’t disconnect the rod unless the power is off cause if there is a fault it can kill you.


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[Crossy]

1 hour ago, Wirejerker said:

Don’t disconnect the rod unless the power is off cause if there is a fault it can kill you.

Thanks for that WJ, forgot the warning.

 

[Crossy]

10 hours ago, longball53098 said:

Actually back a couple years ago when Crossy was reporting on his rod being corroded and it disappeared

I never worked out what happened there, the replacement rod is still sound and reading well.

 

[tutsiwarrior]

with my 'on demand' shower water heater can I be certain that the dedicated heater ground rod is not damaged and functioning if the internal heater ELCB is functioning properly?...I test using the internal heater test/breaker button then check to see that the water goes cold...the dedicated heater circuit takes off upstream of the CU and the RCBO for the main supply and there are 2 intermediate 'bathroom' type breakers upstream of the heater unit...

 

the heater grounding arrangement was installed about 10 years ago for an old unit...

 

 

[Crossy]

4 hours ago, tutsiwarrior said:

with my 'on demand' shower water heater can I be certain that the dedicated heater ground rod is not damaged and functioning if the internal heater ELCB is functioning properly?

No! The RCD/RCBO does not need a functioning ground for the test button to operate.

 

If you can see the rod check the connection looks sound (not corroded) and check the connections in the heater. Without specialist test kit there's not really much more you can do.

 

You could do a quick-and-dirty rod test with a small (about 15W) incandescent lamp. Connect one end to the rod and the other to an unprotected (no RCD) live, if the lamp lights the rod is "good". Disconnect the rod cable and take great care if you decide to do this test.

 

[longball53098]

14 hours ago, Wirejerker said:

The DY207A is giving the correct information and for your setup it shows your earth rod is in the range of 1.8 to 92 ohms. ( it will be in the upper closer to 92 ). Earth loop impedance is the resistance from your live conductor back to and through the tranny where it is earthed on the neutral side then back to your earth. You have elected to use the ground as your return path hence the high reading. An earth fault under these conditions will not trip a normal Circuit Breaker so you must have everything protected by RCDs or RCBOs. To get the earth impedance down you need to connect the MEN link. You are wasting your time doing those tests with stakes at different distances as that is usually only done at the tranny end. If your earth rod looks Okay and is firm in the ground it should be fine and the reading from the 207A shows that it is. If your still not happy bang another rod in and connect to that. Don’t disconnect the rod unless the power is off cause if there is a fault it can kill you.


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Thanks for the feedback. I want to understand you here so? Are you saying that if something plugged in to any socket having a short to ground will not trip a standard breaker? Or take so long that it may cause a fire or ?

 

 

[Wirejerker]

Thanks for the feedback. I want to understand you here so? Are you saying that if something plugged in to any socket having a short to ground will not trip a standard breaker? Or take so long that it may cause a fire or ?
 
 

Yes, that’s correct. That’s why you need a RCD at the front end or a RCBO (or combination of a CB and RCD) on every circuit. At present If you have a live to neutral fault the circuit breaker will trip Okay..


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[sometimewoodworker]

On 12/13/2018 at 8:32 AM, Daffy D said:

 

I think crossy once suggested testing the earth connection by putting a low wattage bulb between the Live and the Earth and it should light up.

 

I did try that once but the Safe-T-Cut tripped so gave up on that at the time ????

That is telling you that the Earth rod is working and so is your RCBO.

 

The RCBO is tripping due to the imbalance in the line and neutral current that is flowing via the earth connection.

 

The only way to get it to light is by disconnecting the RCBO.

[Daffy D]

3 hours ago, sometimewoodworker said:

That is telling you that the Earth rod is working and so is your RCBO.

Two tests in one - I like that 

[sometimewoodworker]

5 hours ago, Daffy D said:

 

9 hours ago, sometimewoodworker said:

That is telling you that the Earth rod is working and so is your RCBO.

Two tests in one - I like that 

 

We'll sort of. The earth is certainly working now as is the RCBO however that doesn't mean that the earthing is good or that it will work in the dry season.

 

it probably will and is probably good, but a proper Earth resistance check is the only real way to be sure, and good luck with getting that.

[Daffy D]

12 hours ago, sometimewoodworker said:

or that it will work in the dry season.

As mentioned previously my earth rod is near the concrete ring septic tank and that area never dries out. so one thing less to worry about.