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Very low Ra reading disappears when connected back up.

aligarjon

Hi Guys

I had some very strange readings today when doing an EICR.   Property is a semi detached cottage in a very rural location. Over head supply. 

The first thing i noticed when i arrived was a piece of angle iron driven into the ground outside the front door with a corroded 10mm earth cable bolted to it exposed for all to see.

The consumer unit is located just inside the front door in a cupboard and i can see the earth cable going out through the door frame.  I disconnected it at the CU and got an Ra reading of just over 2 ohms so i am obviously amazed. I reconnect it to the CU to get a PFC reading etc and the Zdb is nearly 300ohms with the original earth reconnected. I disconnected it again and got just over 2 ohms again. Reconnected it and got around 300ohms.  

This is a new one on me, does anyone know what could be going on ?

Cheers  Gary

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    Rather odd then.

    Can you do a 2 wire Zs  test from  L to  electrode that does not need the neutral connection ?  That would depend on your meter, not all modern ones can.

    I can imagine a low current 3 wire test getting confused if  there is a neutral -earth offset that is the wrong way relative to the L-N phase, but it needs a neighbour on another phase to have significant earth leakage. (so when you add the L-E test current the NE voltage falls rather than rises.)

    (I'm sure you would have noticed if L-N had been reversed but I suppose I should ask that too for completeness .)

    And the really obvious - does that angle iron connect to something better earthed, or even neutral connected, elsewhere either above or below ground, like massive piling or maybe underground water pipes that share with the neighbours half a mile off who for some reason have PME or something.

    It is a puzzler, at least as presented,  it is not obvious.

    Mike.

  • 0 in reply to mapj1

    Earth Electrodes Part 2 - Installing, Loop Impedance Testing - Bing video

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