The advice is indeed to place electrodes 1 to 2 electrode lengths apart, but this is only advice, and sometimes the choice of location is cramped, or maybe the installer is in a hurry and having a bad day - if the reading is low enough it may not really matter.

There is a general recommendation that all fixed wiring is re-inspected at an interval initially specified by the original installer, though that interval is then often varied by the most recent inspection. Typically that may be re-inspect after five years or ten, with shorter times for sites with a lot of exposed wiring outdoors (catenary supplies to outbuildings etc) and TT supplies with earth rods, or other site specific factors that increase the risk of deterioration or damage - being near the sea greatly increases the risk of salt water induced corrosion for example. The regulations do not make a distinction between a visual inspection example forms and a full 'instruments out' job example form, even though NICIEC (a large trade body) do, but clearly if the intention is to only walk around look for damage to cables or enclosures or evidence of damp or corrosion, then this is a less onerous task. An 'full' inspection may sample a small fraction of equipment on the site, or require  total dismantling, rather depending how it looks, and previous reports being available.




At the cheaper end of the market, especially domestic, like the RCD tests, the advice on regular inspection is routinely stretched or just ignored, in preference to calling someone out only after there is a problem, but more up-market customers and businesses with valuable livestock to lose etc,  take it very seriously indeed, not least because their insurance company tells them to do so.Again , at the lower end of the market some of the cheaper (so called 'drive by' ) inspections (not looking in lofts, not verifying insulation resistance, not looking at Zs etc) are of little benefit except perhaps as a liability transfer exercise, as it is all so fast that very little is actually inspected.

The advice is indeed to place electrodes 1 to 2 electrode lengths apart, but this is only advice, and sometimes the choice of location is cramped, or maybe the installer is in a hurry and having a bad day - if the reading is low enough it may not really matter.

There is a general recommendation that all fixed wiring is re-inspected at an interval initially specified by the original installer, though that interval is then often varied by the most recent inspection. Typically that may be re-inspect after five years or ten, with shorter times for sites with a lot of exposed wiring outdoors (catenary supplies to outbuildings etc) and TT supplies with earth rods, or other site specific factors that increase the risk of deterioration or damage - being near the sea greatly increases the risk of salt water induced corrosion for example. The regulations do not make a distinction between a visual inspection example forms and a full 'instruments out' job example form, even though NICIEC (a large trade body) do, but clearly if the intention is to only walk around look for damage to cables or enclosures or evidence of damp or corrosion, then this is a less onerous task. An 'full' inspection may sample a small fraction of equipment on the site, or require  total dismantling, rather depending how it looks, and previous reports being available.




At the cheaper end of the market, especially domestic, like the RCD tests, the advice on regular inspection is routinely stretched or just ignored, in preference to calling someone out only after there is a problem, but more up-market customers and businesses with valuable livestock to lose etc,  take it very seriously indeed, not least because their insurance company tells them to do so.Again , at the lower end of the market some of the cheaper (so called 'drive by' ) inspections (not looking in lofts, not verifying insulation resistance, not looking at Zs etc) are of little benefit except perhaps as a liability transfer exercise, as it is all so fast that very little is actually inspected.