What we should do, and what we do are not the same. In most cases we look at lights and say this 6 amp circuit is no where near the 30 meters which will cause a volt drop of 6.9 volt (3%) if loaded with full 6 amp at end, it will not be full 6 amp at end, it will be spread throughout its length, so looking at more like 60 meters before we are in a problem area.
So we ignore the test, it only needs the loop impedance measuring at the end of run to measure both volt drop and if the line - earth loop impedance is low enough, 3.6Ω for a type C MCB. But with RCD protection does it really matter?
In the main we do the testing we need to do to complete the minor works or installation certificate, and since there is no little box to enter the volt drop or even the line - neutral loop impedance or prospective short circuit current both can be used to work out volt drop, we simply don't do it, we should, but we don't.
To be frank the old method of using the ceiling rose as the junction box it would be a huge house to get over the permitted loop impedance, but wiring switch to switch, one uses a lot more cable, so one could easy hit the limit.
However with a fluorescent lamp with a magnetic ballast the volt drop was important, but with electronic ballast and with LED although regulations say 3% it is not really that important. And I have not seen it measured with an EICR so unlikely to get caught out.
I have seen inspectors remove down lights, and 230 volt down lights need an earth running to them,
A circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed-conductive-parts and suspended from such a point.
has been the rule since 1966, and down lights are not suspended so need an earth running to them even when the fitting is class II, they are fixed, not portable so need an earth.
But it's like saying we should drive at 50 MPH on this road with a trailer does not matter how small, but it is in the country and as straight as a die so I travel at 60 MPH so as not to slow other traffic, that may be the case, but I would be silly to admit it. In fact I know we have police in the air so I don't, but I think you can see my point.
We all know what we should do, we have sat the C&G 2391 and done the course, and we also know it took an hour to test the board for the exam, and if we extended that time to inspect a house, at that level of inspection it would take 2 days. We simply could not charge for that time. I remember going for it with a Robin automated PAT tester, which did its pre test checks every time it was plugged in, and found in 8 hours I could test no more than 80 items, the tester took a fixed time to run through the tests, with class I that was limit. But seen people do 180 items in a day, clearly they were not doing the whole test. Or their tester did not do the pre-test checks.
But we tend to cut corners, it is human nature, but the trick is to know when, and even the official training talks about testing 20% and if no faults that's OK, but any fault test 40%, and if then a second fault test 100%.
So in the main a DIY person should test 100% as he does not have the experience to know when and where there is likely to be faults, but the professional can use experience to reduce the testing, but the professional is more likely to get caught out, Pembrokeshire Trading Standards v Mark Cummins, trading as M C Electrics from Haverfordwest is a good example of where the tradesman went too far in not doing the testing. The £2,600 is not that much, but the publicity will likely continue for years, the newspaper reports are still there to read over a year latter. The Emma Shaw report from 2003 I seem to remember has just disappeared from the IET website. So an error can follow you for 20 years, is it worth it? We look at these reports and often say there by the grace of god go I. I know I allowed the electricians mate to test things for me.
