I have not the latest regulation book so there may be some errors in my statements. But from what I believe the LABC inspector has to follow BS7671:2001 or similar which is not the latest BS7671 edition anyway. That is what the official approved Part P document says anyway. So this is before it was required to have RCD protection for all services to the bathroom which would clearly include most showers and also before the 50mm rules for items buried in the wall. RCD protection was required for sockets which could be used to supply outside appliances and I seem to remember some items in bathrooms.
Today scheme members have to follow BS7671:2008 amendment 3 which would include all cable buried less than 50 mm and all sockets under 32A but there is nothing to say a building inspector has to comply with BS7671:2008. Also the building inspector does not issue an electrical installation certificate only a completion certificate so it is open as to if he actually tests the loop impedance on all circuits.
Often the building inspector will employ an electrician to test and inspect and the electrician is likely a scheme member so will have to work to BS7671:2008 amendment 3 so the report to him would highlight errors like no RCD. If he is employing an electrician to test then he is unlikely to have the skill required to decide if the items highlighted are to 2008 or 2001 so in real terms he has to work to 2008 regulations even if they are not legally a requirement.
But under the Part P regulations I could wire a house to German regulations and the building inspector would have to accept that even though it does not comply with British standards in that sockets are not polarity fixed. I never understood why the Part P document did not say current edition of BS7671 or equivalent?, but it didn't.
As to earth wires there is no need to terminate into class II items but there is a need to run an earth with the line and neutral and also that earth loop impedance must be within limits. Also the line - neutral has limits more to do with volt drop and the idea of RCBO having to be type B, C, or D is open for debate. Since the tripping times with a earth - line fault are from the RCD part of the device just like with a TT system the earth loop impedance can be rather high over 200Ω is considered unstable. So it is the line - neutral fault which the type B, C, or D will need to match the loop impedance to trip in a very short time. Although the regulations gives 0.4 seconds for the line - earth fault I have found no reference to tripping times for a line - neutral fault.
However our switches often have a current rating so using other than type B could overload switches and could cause bulbs to weld into their holders if ionisation happens when they blow. So personally would always fit type B even if not strictly required.
Many inspection sheets do not record all readings taken, the IET version does not so although we should measure both line - neutral and line - earth impedance the fact it is not written down means often line - neutral impedance or prospective short circuit current which is really the same thing using a different unit is often not measured. It is however that measurement which shows what the volt drop will be and so where one has no idea of how much cable has already been used when extending a circuit is rather important to ensure volt drop is between limits and any MCB/RCBO will trip with the magnetic part.
Amendment 3 I am told has reduced the loop impedance permitted to ensure each type of MCB will trip. A type B should trip between 3 and 5 times rated current and we work on the 5 times so a 6A type B will trip with 30A. However the loop impedance takes into account voltage it would seem sensible to read the prospective short circuit current but instead with read the impedance and consider there may be a 5% volt drop so we take 218.5 volt as the working voltage and device that (ohms law) by 30 amp which gives us 7.28Ω as our maximum loop impedance.
However it is the volt drop which is really the limiting factor as with a DNO loop impedance of 0.35Ω any reading over 1.81Ω would mean over a 6.9 volt drop and a type D 6 amp MCB will need an earth loop impedance of less than 1.82Ω so if a lighting circuit complies with volt drop using a type D would not be a problem. The 44 meters of 1.5 mm² cable maximum to ensure a loop impedance is high enough seems a lot, until you start to measure up and down walls and across a ceiling to comply with 1/3 rule drilling the beams.
So in real terms one has to measure. Be it a loop impedance meter reading direct or a low ohm meter and adding the DNO reading given by enquiry it does not matter either is allowed. The LABC inspector however is not required to inspect and test all he has to do is verify some of your readings. He has to satisfy himself you know what you are doing. Hence why he does not have to complete an installation certificate you have to do that, all he does is check so random entries to see if correct.
As to if it all goes wrong who has to foot the bill or stand in court is another question. The LABC inspector is responsible for site safety so if you don't test correctly as with
the Emma Shaw case then he would be in court and he would carry the can. But you would have to pay for the repairs to correct it.
Although we hear of cases where social services have been taken to court because baby x was injured as yet we have not seen the LABC inspector being taken to court because Mrs X was electrocuted. Until this happens it would seem the LABC inspector has rather a cushy number, he gets the money, but very little risk should his judgement be incorrect. Even if he makes a mistake unless he has some qualifications to show he has the skill required it will likely be his boss who is found guilty of using unskilled labour to do the work of inspecting. Hence why they often use electricians to inspect so they can collect the money without any risk to themselves.
Personally I am not worried about what the inspector says what I want is a safe house. So back in 1992 my whole house was RCD protected well before any regulations requiring it came out.
To my mind unless the inspector has a C&G2391 or C&G2392 he should not be inspecting electrics. But when I came to do my dad's house the inspector did not even seem to know what a C&G 2391 was, which means I don't really trust them.
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