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EICR TT installation coded C2 by electrician

Gomez Addams

Hi,


Anybody got any thoughts on this situation?

I have had an EICR done on a property. There were no issues reported apart from earthing. 

The electrician measured the rod resistance at 534 ohms. He insists it has to be less than 200, but his preference is less than a 100.
He said the 30ma RCD wouldn't trip at the measured value, so didn't bother to test it. Bizarrely, he said he pressed the test button which, of course, tripped, but he coded it C2 "unsatisfactory".

I had already tested it with my meter. I got 400ohms, a worst case trip time of 9ms, best 6ms and 28ma on the ramp test.

I pointed out the 200ohms is a recommendation not a requirement and asked him to justify his C2, he refused and stated he stands by his findings.

I haven't checked yet if there is an obvious reason for the rod to be high, but it seems to me the requirements of the regulations have been met.


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  • 0

    I used a a long wire and a ground probe.

    Just one wire? How did you account for the resistance around your test electrode? Was that on a d.c. Ohms range? The salts in the soil and metals of the electrodes can often make little batteries, generating a small voltage that can easily influence the result of a simple d.c. test (you might well see differences simply by reversing the meter connections). The resistance around a temporary electrode is usually considerable - a 4-wire (or sometime 3-wire) test method using separate test electrodes for voltage and current and an a.c. test current is usually needed for dead testing of electrodes to get sensible results. Loop testing (from the mains L) is usually simpler - although it does include the resistance of the source electrode (e.g. at the substation & for PME additional electrodes in the distribution system) - which can yield higher figures than your electrode alone, the difference is normally small.

       - Andy.

  • 0 in reply to AJJewsbury

    Sorry, my statement before was a bit brief.


    The meter has a jack socket to plug the probe into. The 2 wire test lead is used to do this as per Megger's instructions. The equivalent circuit in the user manual shows how the resistance is measured. So one lead is on the rod, the other on live and the long lead is on the probe. Current is injected into the rod and the probe in parallel. The meter the current injected and the developed voltage are used to calculate the resistance. It is a loop measurement, but with a "true" ground reference as the manual puts it. I did try the probe in more than one spot and the results were comparable.

    The local substation here is about 250M away. 

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  • 0 in reply to AJJewsbury

    Sorry, my statement before was a bit brief.


    The meter has a jack socket to plug the probe into. The 2 wire test lead is used to do this as per Megger's instructions. The equivalent circuit in the user manual shows how the resistance is measured. So one lead is on the rod, the other on live and the long lead is on the probe. Current is injected into the rod and the probe in parallel. The meter the current injected and the developed voltage are used to calculate the resistance. It is a loop measurement, but with a "true" ground reference as the manual puts it. I did try the probe in more than one spot and the results were comparable.

    The local substation here is about 250M away. 

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