Previous test may have been done with parallel paths in place.
I'm also going to stick my neck out here, does the circuit you installed have RCD protection? If yes then you could rely on the RCD to cover for the poor earth as a short term solution until the earthing problem is rectified. I know some will frown upon this but for me it would only be a temporary fix.
The DNO may well say convert to a TT and you could end up with an even worse Ze (Ra).
The circuit I installed was a 4mm SWA to CU in summer house. The consumer unit supplied a lighting circuit via 6amp mcb and RCD main switch
I discussed the temporary RCBO as a safety precaution for the supply SWA but explained ultimately it still isn't adaqute due to ZE.
My concern is the change in ZE from 2010. The homeowner said nothing has been changed since 2010 when they had the 2nd consumer unit installed. Which means the clamp for the earth was existing (this is a bonding clamp).
I did 2 tests, ZE was 2.70Ohms, I also did a loop test with all earths connected and I got 1.27Ohms. The 0.15Ohms and 2.2PFC from their install cert in 2010 must be either rubbish or there has been some change somewhere.
Ive issued a cert showing all my dead tests and sent them the DNO contact I use to arrange a check.
It’s perfectly possible that a cable joint has degraded, leading to a rise in the external loop impedance.
As has been said, one for the dno to sort out; might convert to pme or tell you to put in a rod.
I think the previous figure can be "assumed" to be correct ..... suppliers cables DO become faulty ............
The issue needs to be reported to the supplier and see what they say/do ............
Whether you can justify not energising the new circuit is debatable ........ I guess it will be how you dealt with describing the issue to the customer ....
The electric is resisting that Proteus board.
But seriously did you try testing with the probe on the sheath itself? Bonding clamps should not be used on cables as it can do mechanical damage when tightened and as the temperature can expand and contract the cable making the connection loose. There also may be corrosion between dissimilar metals.
Hopefully a lesson learnt here, always carry out some pre job testing like Ze so you dont leave a job unfinished while expecting the customer to pay you for it.
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