Strange measured Zs Readings!?

[securespark]

Nor did the old rule 'always test RCDs with the loads disconnected' until one failed on 1x and 5x, disconnected a refrigeration load and it was well within spec (was a brand new Schneider RCBO so it should bloody well pass!)

Yeah, I had that too. Funnily enough with an old MK CU.
It failed 1/2 x test and the Zs was too high, but when tested in isolation, it flew through the tests.

 

[eveares]

I hope you didn't use a socket adaptor with a link between L&E and then test the resistance at the consumer unit end?

Yes, I did why? I of course disconnected the CPC from the earth bar in the CU and connected it to the alligator clip of my MFT; all MCB's & RCD's were also switched off during taking the reading.


I even tried to re-energise the 32A MCB after I was done, forgetting that my R2 socket adapter was still plugged in!

 

[John D v2.0]

My guess is as @Iggifer there's a parallel earth path somewhere helping out. Is there a boiler or something nearby on that circuit connected to the gas or water pipe and via next doors bonding?
Not sure about a parallel live path though, that would seem less likely, and would be needed to get that reading. Maybe zdb with bonding connected would be 0.01 ohm and all the impedence is in the earth, what's the PFC?