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Right, I think I've nearly got to the bottom of this with the electrician now.
When I asked him about the various differences between the 2008 report and his, he noted the following:
- The 2008 report showed a very low (almost non-existent) for insulation resistance on the heating circuit - which would seem to imply that the other electrician also struggled to get a meaningful reading (or any reading at all) out of that circuit;
- The 2008 report did however show what appears to be suitable Zs readings for the heating circuit and the off-peak water, something which my current electrician hasn't able to manage. He's unsure how the previous electrician would have got such a reading given the lack of power and the switches/timers (ie isolation) in the circuit;
- I also queried why he hadn't tested the continuity (Ring final circuit continuity in respect of the "sockets" circuit, and R1+R2 continuity for all circuits) in his report, when the previous electrician had. His response was "There’s no need to do continuity testing on a periodic. If the testing of Zs and Insulation Resistance gives good results, then that really proves a safe circuit which is the aim of the exercise. BS7671 merely states to undertake ‘appropriate tests’. If another sparky chooses to do continuity, that’s up to him but it’s always down to discretion and appropriateness."
So his stance on the heating circuit seems to match up with the outcome of the 2008 report.
I'd be grateful if any of you have any comments on the 2nd point (regarding the inability to test Zs) and 3rd point (whether continuity testing is/isn't part of a periodic test)!!
With regards your first point, an insulation resistance reading is a dead test (conducted with power off) so your electrician could have done this test, I am unsure if he did or not? Also, a low insulation resistance result does not mean that he had difficulties obtaining the result, it means he tested it and that was the result he got. A result of 1MΩ or greater is acceptable, and a result of below 1MΩ means that circuit requires attention.
With regards your second point (the Zs readings) as Richard has said the original electrician may have just calculated this from looking at the Ze result and adding it to the R1+R2 result (so it could be obtained with the power to the heating circuit off). You could perhaps look at these 2 results (Ze and (R1+R2)) and if added together equal 'exactly' the result he has put for Zs then he 'may' have just calculated the Zs (unless coincidentally that was the measured Zs, but unlikely). Ze may be written as 'Zs at DB' on the report that you have.
So, with the power to the heating off your electrician would not be able to carry an actual 'measurement' of the Zs, but he could carry out an R1+R2 of this circuit and add it to the Ze (to obtain a calculated Zs).
Again, as Richard has said not all electricians will carry out a R1+R2 on a report if they get a satisfactory Zs so i dont think your electrician should be penalised for this, but an R1+R2 on the heating circuit would have been necessary as no Zs was obtained.
Lastly, it's very difficult to give 100% guaranteed advice without seeing the installation.
It would be interesting to know how long the electrician was there for and how much he charged?
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