Multiple Earth Electrodes Test Results

I need to clarify something that's rattling around in my head.

I was taught when testing lightning protection systems that the maximum permissible combined electrode readings shouldn't be over 10 ohms. So we would test all the electrodes individually then work out resistance in parallel.

We now have to test street cabinets and part of the DNO requirement is that supplementary electrodes have to be installed and the resistance must be below a certain amount dependant upon the cabinet loading if TNC-S earthing is used. Normally if the reading is over the maximum permitted we would convert to TT as per our customers policy, easy enough.

However we are now having to install additional electrodes, normally using conductive concrete as opposed to rods, to try and get the resistance down to maintain the TNC-S earthing arrangement. This removes the need for RCD protection on telecoms equipment and takes away the risk of nuisance tripping.

Here's where I'm getting confused. If I tested a site with two electrodes and got 48 and 52 ohms on each and my maximum permitted is 47 then the site would be classed as a fail as the lowest results is still above the maximum. This is using test method 3 from GN3, EFLI test, the tester would only show the path of least resistance.

However if I work out resistance in parallel my result is a pass: 1/48 plus 1/52 = 1/0.03 = 33.33 ohms.

So which is the correct result?

I've also posted this on another forum to see what hilarious answers come up... 

The combined result is correct. In normal operation the electrodes are permanently connected.

The best way of testing would be a “fall of potential” test but in a residential area you’ll need a Jack Hammer in your tool kit.

surely the whole point of multiple rods is to drop the overall resistance  by providing parallel earth paths?