At 534 ohms, the Ra is well within 7671 requirements, but is the value stable and reliable? Might there be a reason why it is relatively high, is it in to loose soil, poorly connected etc?
The Ra at my own house was around 300 ohms when last tested but I have made several tests over the years and was able to confirm that it was a consistent result. 
I live in the foothills of the Mourne mountains with rock bursting through parts of the garden, not so good for sinking rods. 

There are situations where a reading that high can mean the electrode has all but corroded away, but at 500 ohms it would trip the RCD and is not an immediate fail.

As described, I would suggest 'needs improvement' C3 or at least 'needs investigation' but there may be other things we cannot see that concerned him.

If the soil is very dry and sandy or shingle, it is entirely reasonable to get a reading of some hundreds of ohms from a single electrode, and in that case a rod may be the wrong thing, but  arguably in such places it is also hard to get a shock to true earth as well and of little concern.

Mike.

The ground is well compacted. The rod is close to the house wall driven down the side of the concrete yard. The houses are well over 100 years old and have no footings and also the ground is about 2 ft lower than the garden to the rear which is chippings so free to drain. There is no chance it could freeze or dry out under the concrete, except in exceptionally severe weather.  The area is pretty flat and below the soil there is a lot of sand. I have three other properties within 100M and they about 100 ohms or lower. I haven't checked yet, but I'd be more inclined to suspect the termination on the rod.

I'd agree that there's no issue with 30mA RCDs tripping at the reported value - it should actually trip (eventually) at 7666Ω and within 0.2s at half that. 1667Ω is to ensure that the earthing system can't float around at over 50V without the RCD ever tripping.

400-500Ω is around 5x to 10x higher than I'd get for a simple 4' rod sunk into half decent soil around here - so unless there are extenuating circumstances it certainly should be ringing bells for 'maybe there's something not quite right there' (rather like getting a couple of MΩ.insulation test on a brand new PVC circuit with nothing connected).

There's also the issue of reliability - soil resistance can change considerably with weather - dry or freezing can make the top part of the electrode useless - if it's looking dodgy after a wet winter, what's it going to be like in a drought or a prolonged cold snap? 200Ω (or some say 100Ω) is supposed to be a good indication that a decent length of rod has reached strata that's likely to be reliable in the long term.

As for the coding, it's not immediately dangerous - so definitely not a C1. Could it be dangerous under single fault conditions? - possibly (e.g. if the Earth connection if the reading is an indication that it's hanging on by a single corroded strand and it could fail completely at any moment (especially if standing protective conductor currents from an entire installation could be enough to make the earthing system hazardous live)  So maybe a C2, if not certainly C3 - but it depends on a few factors we can't see.

   - Andy.

FI is probably a better code, still a fail but certainly worth investigating.  If it gets a C3 nothing will get done about it and it could fail if there is an issue other than just a rocky or sandy area.

Gary

Opinions don't matter, only the regs and the facts: it doesn't matter what some say. The resistance is well below maximum and the disconnect times are compliant. I would say (intended) no justification for C2. C3 or obs. The best practice guide states C2 if the RCD does not trip, it does.

FI should only be used (see best practice guide) if a determination can not be made. The installation is compliant with the the max resistance and the disconnect times are more than adequate. The requirement is "is it safe" not "is it perfect". 

Err, and is it reasonable on the evidence presented to expect it will it stay safe and regs compliant until the recommended date of the next inspection, assuming no unnatural abuse  ? You may prefer a very short retest interval ?

Now if that high Z is due to sandy or stony ground and the electrodes and connections to them are in good order fair enough. If however it is in soil that normally gives 50 ohms for a 4 ft rod, then something is wrong, and it may in fact be almost corroded away and hanging by a thread and ready to fail at any moment. The meter alone cannot tell - the mk1 eyeball and perhaps a bit of a waggle of the electrode(s?) and associated clamp(s) is the level of 'FI' needed here.

M.

Opinions don't matter, only the regs and the facts: it doesn't matter what some say. The resistance is well below maximum and the disconnect times are compliant. I would say (intended) no justification for C2. C3 or obs. The best practice guide states C2 if the RCD does not trip, it does.

You can't read BS 7671 alone for these things - for things like Earthing it defers out to other standards - e..g. BS 7430 (e.g. see note to reg 542.2). The test button on the RCD normally doesn't prove the Earthing system as they are typically connected to supply N rather than PE (to prevent unwanted tripping of upstream RCDs during the test). In any event there's more to safety in a TT system than just the RCD tripping - as above, the Ra limits are set by consideration of touch voltages rather than tripping times. Also EICRs aren't meant to be simply a snapshot of that state of the installation at a single instance of time - they're meant to be a judgement of whether the installation is suitable for continued service (i.e.until the next inspection) - if there's a reasonable suspicion that a gradual degradation might be occurring then the inspection could either say it isn't satisfactory, or put a time limit on things such that it's likely to remain safe for that time (e.g. next inspection in 1 month or 6 months, rather than 10 years) - which you'd likely find just as objectionable. For the electrician's point of view if it did go horribly wrong  before the next inspection and there was clear evidence that things weren't right at the time of his inspection, he could well end up in court having to account for his judgement.

   - Andy.

I think you missed my point. The electrician said he didn't do the RCD trip tests as he said it couldn't trip with that resistance. It trips on the button and it trips on my meter on all tests. There has never been any nuisance tripping at the house.

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