Measuring electrode resistance to earth using loop impedance tester?

[Stormflex]

I'm going to be fitting a new CCU where the earthing arrangements at the property are TT. Obviously I will need to measure the electrode resistance to earth and as I don't have an earth resistance tester I was hoping to do it as described below.

I assume the result is the number I enter on the EIC?

Regarding the bit I've underlined, I read this as a verification that the result achieved above is of an acceptable level and isn't actually recorded on the EIC or in the schedule of test results?

I take it I perform a Zs at the last ceiling rose or socket (I guess both and then use the one with the highest Zs?) on the circuit and then add this to the electrode resistance? Finally, apply RA I(delta)n </equal to 50V?

Using an earth fault loop impedance tester
The tester is connected between the phase at the origin of the installation and the earth electrode under test as shown in {Fig 8.16}. The test is then carried out, the result being taken as the electrode resistance although the resistance of the protective system from the origin of the installation to the furthest point of the installation must be added to it before its use to verify that the 50 V level is not exceeded. If an RCD with a low operating current is used, the protective system resistance is likely to be negligible by comparison with the permissible electrode resistance.

Fig 8.16 - Measurement of earth electrode resistance using an earth-fault loop tester​

It is most important to ensure that earthing leads and equipotential bonds are reconnected to the earth electrode when testing is complete.

 

[SimpleSimon]

If you don't own an electrode resistance tester you can use your earth fault loop impedance tester and measure the resistance exactly the same as a Ze.
Ie disconnect the main earthing conductor so you have no parallel paths and test between live neutral and earth if you have three leads or live and earth if you have two.
Your results to be satisfactory should be under 200 ohms.
This should be recorded in the EIC in the schedule of test results and inspections.

 

[IQ Electrical]

I'm going to be fitting a new CCU where the earthing arrangements at the property are TT. Obviously I will need to measure the electrode resistance to earth and as I don't have an earth resistance tester I was hoping to do it as described below.

I assume the result is the number I enter on the EIC?

Regarding the bit I've underlined, I read this as a verification that the result achieved above is of an acceptable level and isn't actually recorded on the EIC or in the schedule of test results?

I take it I perform a Zs at the last ceiling rose or socket (I guess both and then use the one with the highest Zs?) on the circuit and then add this to the electrode resistance? Finally, apply RA I(delta)n </equal to 50V?

Using an earth fault loop impedance tester
The tester is connected between the phase at the origin of the installation and the earth electrode under test as shown in {Fig 8.16}. The test is then carried out, the result being taken as the electrode resistance although the resistance of the protective system from the origin of the installation to the furthest point of the installation must be added to it before its use to verify that the 50 V level is not exceeded. If an RCD with a low operating current is used, the protective system resistance is likely to be negligible by comparison with the permissible electrode resistance.

Fig 8.16 - Measurement of earth electrode resistance using an earth-fault loop tester​

It is most important to ensure that earthing leads and equipotential bonds are reconnected to the earth electrode when testing is complete.

Yes, exactly what SS has said above, the value you measure is actually termed RA on your EIC and should be below 200 Ohms for stability.

Assuming 30mA RCD protection on all sub-circuits, this gives you a maximum Zs value of 1667 Ohms-regulation 411.5.3 is met where this is the case.

 

[Stormflex]

Thanks for your help guys

 

[IQ Electrical]

Just an afterthought, I presume this is test between live and neutral at the main swith and the disconnected earthing conductor?

Between line and the earthing conductor at the main switch