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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.


  • 0
    Gomez Addams said:
    The electrician measured the rod resistance at 534 ohms.

    How did he do that?

  • 0 in reply to Gomez Addams

    In his defence, Megger (and probably all the others) won't run the RCD test if the touch voltage will exceed 50V, which it would if he tried a 5x test (or auto).  What meter are you using, and what RCD tests did you do?  Is there a front end 100mA RCD, time delayed or otherwise? 

  • 0 in reply to AJJewsbury

    He said he did not test the RCD trip times. He put >300ms on the report. My worst case trip time was 9ms. I don't think it's gone from 400 to 534. He loop tested it, I used a a long wire and a ground probe. I don't think it is unstable, but I will test it again after the weekend.

  • 0

    Hi,

    Not a C2 unless the RCD is faulty, which would be a rare occurrence but not impossible. I the last 3 months I have  had to replace two that no longer worked. It certainly is preferable to have an electrode resistance of lower than 100 ohms if at all possible. Got mine at home down to around 67 with 2 pairs of 5/8" rods.

  • 0

    The electrician said he didn't do the RCD trip tests as he said it couldn't trip with that resistance.

    I'd agree that wasn't an accurate explanation at all (although I've heard worse when an electrician is trying describe electrical matters to a customer who may or may not be technically minded), and he might even not fully understand all the implications accurately himself and be over-relying on rules of thumb. Sounds like -1 for customer relations.  But even if his thinking is flawed, it doesn't necessarily follow that his final answer is exactly the reverse of what it should be.  The bottom line is I wouldn't want to give a clean bill of heath to TT system where there is reasonable suspicion that the earthing facility was showing signs of failing. As others have suggested, FI may well have been more appropriate than C2 - but both will give an unsatisfactory until more work is done anyway. If it's gone from 400Ω to 534Ω in the space of time between you both doing your respective tests, what's is lit likely to be in a month, at the end of the summer or next year? Can you really be reasonably sure it'll still be below 1667Ω? If not, how can anyone to state that the installation is satisfactory for continued service?

       - Andy.

  • 0 in reply to AJJewsbury

    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. 

  • 0

    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.

  • 0 in reply to Gomez Addams

    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.

  • 0 in reply to aligarjon

    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". 

  • 0 in reply to AJJewsbury

    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.

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