Measuring the earth rod resistance with an efli tester

TONY144 · Posted: Sun Apr 06, 2008 7:18 am

does anyone know please if it is possible to test the value of the earth rod resistance Ra I believe using a 3 lead tester on an efli robin tester because the niceic book and other literature i have seen only shows a 2 lead tester on phase and earth rod ? any suggestions

Thankyou

sparkybird · Posted: Sun Apr 06, 2008 10:08 am

yes, IIRC look in Guidance Note 3 (testing and inspection) at method 2 for Ra testing.

Someone has nicked my copy or else I'd tell you the page!

SB

TONY144 · Posted: Sun Apr 06, 2008 11:30 am

sparkybird wrote:

yes, IIRC look in Guidance Note 3 (testing and inspection) at method 2 for Ra testing.

Someone has nicked my copy or else I'd tell you the page!

SB

thanks will look

cheers

Tony

Spark123 · Posted: Sun Apr 06, 2008 5:15 pm

Put the black test lead on Neutral

TONY144 · Posted: Sun Apr 06, 2008 9:40 pm

Spark123 wrote:

Put the black test lead on Neutral

That will give the ze reading i believe and not the resitance value of the earth electrode but correct me if i am wrong

Spark123 · Posted: Mon Apr 07, 2008 4:37 pm

What is the Ze in a TT system?
The black (neutral) is required to power the instrument and in some instances such as DLOC for the electronics to lock the RCD.

plugwash · Posted: Mon Apr 07, 2008 7:18 pm

Spark123 wrote:

What is the Ze in a TT system?

Assuming you measure with main bonding disconnected it is the output imedanace of the suppply transformer plus the impedance of your live supply condutor plus the impedance of your electrode plus the impedance of your suppliers electode.

In practice the impedance of your rod is likely to be much higher than any of the other things mentioned above and it is normal to use the Ze measurement as a conservative estimate of the impedance of your rod.

testing earth rod resistance seperately requires a different type of tester and several temporary test electrodes but there is rarely any reason to do it.

Spark123 · Posted: Mon Apr 07, 2008 7:26 pm

Yep, what is the difference between a Ze measured with a 3 wire efli tester and a Ze measured with a 2 wire efli tester?

TONY144 · Posted: Mon Apr 07, 2008 8:59 pm

Spark123 wrote:

Yep, what is the difference between a Ze measured with a 3 wire efli tester and a Ze measured with a 2 wire efli tester?

Thanks lads between you all i now have the answer to my initial question.