Earth electrode resistance

[MikeJ42]

Hi, wonder if somebody could advise.
The Robin Domestic Installation Certificate asks for both the 'Electrode Resistance' and the 'measured Ze'. If I am using a simple Fluke 1651 multimeter to test the Electrode Resistance (between phase and the earth rod), the 2 figures will be the same wont they?
Am I missing something?
Many thanks, Mike.

 

[ricicle]

If you do a proper Ze test (with earthing conductor disconnected from the installation/main switch open) then this is deemed as a satisfactory method of measuring the external impedance including earth electrode.

 

[MikeJ42]

Thanks for the confirkmation. So both boxes on the certificate would have the same entry? In this case 10 ohms.
Regards, Mike.

 

[securespark]

I would say so.

Although why your cert words things that way I'm not sure.

Sure it's not an either/or??

You either have a Ze (TN- systems) or an electrode resistance (TT systems). To my mind they are effectively the same thing, namely the resistance of the external earth loop path.

 

[ebee]

I tend to agree with that.
You could power off, disconnect earth rod and test it with an earth electrode tester tgo get an approx figure of Ra.

Or you could do an EFLI test and this would include Ra plus the phase and transformer impedances but seeing as these are very low compared to the rods own resistance the figure you would get in a ideal world with a hypothetical exact tester would be very minimal and your result would be fractionally pessimistic and therefore acceptable.

In fact, a far more important thing to consider is that at the time of testing ground conditions would probably not be at their worst case condition. If you could test in the dryest of conditions at the end of a very long hot spell of weather or during loads of sub frost then you might get a worst case then and the rest of the time "things can only gat better"