In my world of work albeit a specialised area with its own technical guidance this is what we request no matter what BS7671 may indicate or other resistance values to get RCD tripping times.

"Where earthing of the installation is provided by a local earth electrode arrangement (see section 9.8.2), the earth resistance of each earth rod, plate or tape has to be separately tested. The measurements are to be recorded for future comparison, together with a means of identifying the individual items. This test of earth electrode resistance is a pre-commissioning test which should be carried out using an earth electrode resistance test instrument prior to the installation being energised. An earth fault loop impedance test instrument, which requires a source of supply to be available to the installation, is not appropriate for this test. The earth electrode resistance of an individual earth rod, plate or tape at a filling station in the UK should normally not exceed 100 Ohms. If the value does exceed 100 Ohms it may be unstable. The cause of the high reading should be investigated and rectified (e.g. a better electrode may be required). In any event the product (multiple): R_A x RCD rated residual (tripping) current, (I∆n), in amperes should not in any circumstances exceed 25, where R_A is the aggregate earth electrode arrangement resistance. R_A should not exceed 20 Ohms. (Note: Where lightning protection is installed, the value should not exceed 10 Ohms). A lower value may be required, depending on the rated residual (tripping) current of the RCD selected."

Records also need to be kept for the life of the installation so that any sudden or gradual degredation can be monitored and acted upon, so if a Electrode reading has been say at 7 Ohms every year for ten years then suddenly goes to 98 Ohms then something has happened that needs further investigation especially if ground conditions wet/dry/frozen are also recorded, so a competant inspector would act upon that review of test results. Only having the one set of results may not show that degredation.

So Gomez,

You indicated the ttest electrician recorded 534 Ohms, what was the value recorded from the initial installation and testing of that electrode and each subsequent EICR value recorded? or do you just have that one reading?

GTB 

In my world of work albeit a specialised area with its own technical guidance this is what we request no matter what BS7671 may indicate or other resistance values to get RCD tripping times.

"Where earthing of the installation is provided by a local earth electrode arrangement (see section 9.8.2), the earth resistance of each earth rod, plate or tape has to be separately tested. The measurements are to be recorded for future comparison, together with a means of identifying the individual items. This test of earth electrode resistance is a pre-commissioning test which should be carried out using an earth electrode resistance test instrument prior to the installation being energised. An earth fault loop impedance test instrument, which requires a source of supply to be available to the installation, is not appropriate for this test. The earth electrode resistance of an individual earth rod, plate or tape at a filling station in the UK should normally not exceed 100 Ohms. If the value does exceed 100 Ohms it may be unstable. The cause of the high reading should be investigated and rectified (e.g. a better electrode may be required). In any event the product (multiple): R_A x RCD rated residual (tripping) current, (I∆n), in amperes should not in any circumstances exceed 25, where R_A is the aggregate earth electrode arrangement resistance. R_A should not exceed 20 Ohms. (Note: Where lightning protection is installed, the value should not exceed 10 Ohms). A lower value may be required, depending on the rated residual (tripping) current of the RCD selected."

Records also need to be kept for the life of the installation so that any sudden or gradual degredation can be monitored and acted upon, so if a Electrode reading has been say at 7 Ohms every year for ten years then suddenly goes to 98 Ohms then something has happened that needs further investigation especially if ground conditions wet/dry/frozen are also recorded, so a competant inspector would act upon that review of test results. Only having the one set of results may not show that degredation.

So Gomez,

You indicated the ttest electrician recorded 534 Ohms, what was the value recorded from the initial installation and testing of that electrode and each subsequent EICR value recorded? or do you just have that one reading?

GTB