I fully intend to check after the weekend if there is an issue with the connections to the rod, and if not pop a second rod in. I have four houses on TT in a radius of less then 100m. 3 are fine this ones not. I really don't think the ground conditions are going to be significantly different in such a small area.

I'm not disputing that the value is high and lower would be better. I am disputing the C2 and the "potentially dangerous" that comes with it.

As an aside. My own house is one of the 4 on TT. When my kids were little they said they could feel a tingle when the were washing their hands. We are on a plastic water supply. I felt nothing, but I measured everything and found nothing untoward. Eventually, I felt it too when I had a cut finger. It wasn't off the taps or the steel drainer, it was in the running water. I suspect they could feel it because they didn't have hands like leather. I got rid of it with 20m of copper under my front garden. The touch voltage was about 30V to start with, It was about 3V when I was done. Insulation measurements were all good. I was never sure where leakage came from. I suspect it was any or all of fluorescent tube fittings, fridge freezers or switching power supplies.

Gomez Addams said:

It trips on the button

That doesn't depend on an earth connection in most, if not all, RCDs.

Gomez Addams said:

No justification was given for the C2. When asked he would not discuss it. He just stated it has to be below 200 ohms. 

I don't think there's a point in arguing this. In TT systems, Regulation 643.7.1 b) is used to verify effectiveness of automatic disconnection of supply (for protection against electric shock).

This first requires measurement of earth electrode resistance as per 643.7.1 b) (1). BS 7671 (Note to Table 41.5) and the relevant IET Guidance Notes all say that an earth electrode measurement exceeding 200 Ω indicates the earth electrode resistance is possibly not stable.

The next step of testing ADS in TT systems relying on RCDs, according to Regulation 643.7.1 b)(2), is to test the RCD. The guidance in IET Guidance Note 3 for RCD Test Method 1 (test between live conductor and cpc downstream of RCD) implies it may not be safe to conduct the test if the EFLI exceeds the maximum limits (in the case of earth electrode, that would imply check the earth electrode is stable before testing).

Therefore, it may be the case that the person carrying out the test considered it not safe to proceed with RCD tests. It would be a potential breach of health & safety legislation for them to proceed with the tests if they believed it was not safe to do so.

Perhaps there are two ways to proceed from here:

1. Carry out some work to reduce the earth electrode resistance (e.g. repair, replace, or supplement with a second electrode ... doesn't have to be a 'rod' but installing in accordance with BS 7430, at a suitable depth, is strongly recommended).
2. Get a second opinion.

The comparison with the neighbouring properties is the killer information actually.

- while others "400-500Ω is around 5x to 10x higher than I'd get for a simple 4' rod sunk into half decent soil around here "

I have worked in a (dry sandy) place where we sunk two sets of 8 foot rods in parallel about one rod length apart, and still only  just got down to about 200 ohms, varying a bit with method of measurement (I think 340-370 or so per single rod). Equally, a few years ago now I did some electricals at the Essex Scout Jamboree, and in the ever damp Essex clay we saw 80-100 ohms off half length rods (2ft) adequate results from container gensets dropped on their skids even with no electrodes, and  single figure ohms from a metal framed marquee.  So what is OK really varies with location.

Mike

Ze measured at 0.27. On the report the spark added the rod resistance to the Ze.

The touch voltage won't exceed 50 at 534Ohms @ 30ma. One of the tests I did measured the touch voltage at 13v @ 395 Ohms.

Megger CM500. All of the RCD tests, 1/2, I 0/180/, 5I 0/180 and ramp.

You picked out it trips on the button. I also said it trips on RCD tests too, all of them, and in less than half the limit.

I didn't know until later when I spoke to my tenant that he had told her "he didn't have the right equipment with him to do all the tests". So what didn't he have? RCD tester?

Also, the reports say 25% of accessories sampled. Another of my tenants told me, he didn't see the electrician remove any fitting whilst he was there.

I have zero confidence in anything he has said or reported. I have been through these properties myself in minute detail. I have no doubts they are safe.

Yes but it is exactly that, a guide. It isn't electrics for dummies. You still need to use judgement and common sense. You said you have 3 other properties in the area with spikes where the readings are acceptable. That to me indicates there may be a problem with the spike.  I would FI it with local knowledge. 

Gomez Addams said:

You picked out it trips on the button.

Because that makes no odds to testing for BS 7671 conformity, which requires two steps as I said:

1. Earth electrode test; and
2. Then, if safe to do so, RCD test.

Gomez Addams said:

I also said it trips on RCD tests too, all of them, and in less than half the limit.

I also said it may be considered unsafe to do that test, if the earth electrode test  (or a loop impedance test) is not satisfactory. The electrician has to abide by the Electricity at Work Regulations whilst at work ... that may or ,may not apply to yourself, and I'm not questioning that.

As far as BS 7671 is concerned, the electrician may have considered the verification for ADS failed at "step 1" and stopped there (which as I have said, may be difficult to argue with if one has no other knowledge of the installation, as is the situation for myself and other posters here).

I'm not sure why going round in circles will change anything ... BS 7671 has criteria in Regulation 643.7.1 b), which the electrician obviously considered are not met, and just pointing at "step 2" of the verification in Regulation 643.7.1 b) doesn't change the status of "step 1" of that Regulation (at least in the eyes of the original electrician).

Gomez Addams said:

I have no doubts they are safe.

Whilst I wouldn't want to contradict you, as you have knowledge of the installation, I am discussing the criteria in the Standard we are supposed to be inspecting and testing against?

Gomez Addams said:

I didn't know until later when I spoke to my tenant that he had told her "he didn't have the right equipment with him to do all the tests". So what didn't he have? RCD tester?

Also, the reports say 25% of accessories sampled. Another of my tenants told me, he didn't see the electrician remove any fitting whilst he was there.

I have zero confidence in anything he has said or reported.

I'm not sure there's enough to go on here for me to comment further, and of course you'd need to make your own decision on each of these things.

However, in your original post, you only questioned the RCD test ... you said you believed the criteria are met, but I think on that particular point, the electrician may have been following the criteria as stated in Regulation 643.7.1 for TT systems?

Gomez,

Im not really sure why you came onto the forum and asked for an opinion from other Forum members, many of whom are well known BS7671 Experts and have input into that standard as well as others. All you have done has discounted their advice and indicated in your post above that "I have no doubts they are safe"!! if that indeed is the case why not carry out the EICR's yourself and issue the reports and take the responsibility for what you are reporting? or If you feel that the EICR's have not been carried out correctly then raise a complaint with the local trading Standards Department over the quality of the inspectors EICR Report.

I have tested thousands of TT earthing systems over my career albeit within a flammable atmosphere installation, where we certainly depend on the three or sometimes four levels of RCD current and time cascading to ensure protection and compliance.

I would have raised an issue on any single electrode over 200 Ohms in value in fact in my specalised area of work we deliberatly state that any electrode giving a reading above 200 Ohms is likley to be unstable and actually indicate that no single electrode should be above 100 Ohms. So I agree C2 was likley a fair remark albeit FI would have been appropriate, was the ground conditions i.e wet, dry, cold, frozen mentioned when the test was carried out as if this reading was obtained when damp/wet then readings will only get worse as soil drys out.

Why ask for opinions then disregard and criticise those trying to assist on this forum.

GTB

Gomez Addams said:

Ze measured at 0.27. On the report the spark added the rod resistance to the Ze.

Doesn't make sense if it's TT ... unless it's not TT ... or the "Ze" is to the Neutral, or only part of the installation is TT ?

Reasoning ... in TT, the earth electrode resistance R_A is part of the earth fault loop impedance path Z_e ?

But without seeing the whole report, it's not easy to tell ... the original post was just picking on ADS for TT and contradicted this "new" information.