EICR TT installation coded C2 by electrician

Question

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.

gkenyon · Answer

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 &Omega; 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: 
 
 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). 
 Get a second opinion.

gkenyon · Answer

Gomez Addams said: The IET wiring regulations have no force in law. They are not statutory. 
 Agreed ... BUT: 
 
 BS 7671 is mandated by legislation (Regulation 22 of ESQCR) for the whole installation, if you have generation operating in parallel with the public distribution network (e.g. Solar PV). 
 BS 7671, as a British Standard, is used as evidence in court for relevant cases involving installations within its scope. 
 
 Gomez Addams said: The requirement is it "safe". EICR is not a requirement. It is a possible method. 
 OK, but if one uses another method, worth being prepared to defend that position. At the moment, the view that reliance on the RCD without an effective means of earthing is OK goes against all the published guidance (including BPG4 which you quote - see below). 
 
 Gomez Addams said: The question was if the resistance is in spec and the trip times are adequate, where is the potential danger? 
 The guidance says there may well be, and I'm sorry if you don't like the fact that I've pointed out that the means of verification prescribed i n BS 7671 hasn't been met for this installation (and provided a credible reason why the electrician didn't carry out the RCD tests themselves). 
 Gomez Addams said: Best practice guide 4 cites C2 for RCD not tripping. It says nothing about rod resistance above 200 ohms. 
 BPG4 actually says C2 for: 'Absence of a reliable and effective means of earthing for the installation.' 
 ... it's the first entry under C2 
 As discussed, the technical guidance for inspection and testing, and BS 7671 itself, advises earth electrode resistance > 200 &Omega; may not be stable. 
 
 Apologies if you're offended by my opinion on this topic, but it's sadly not going to change without seeing the installation in question for myself.

EICR TT installation coded C2 by electrician

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