Outbuilding consumer unit

The question of short circuit protection needs a reference to the adiabatic equation, where you will find the lighting circuit (even if 1mm2 cable) is safe from that point of view on a 32A Circuit breaker (presumably type B although you have not mentioned it). So it is very unlikely that even a short would cause the cable to fail, and even if it did due to some other defect the result is not catastrophic. To have a "Dangerous" or Potentially Dangerous" situation is not quite so easy as is often imagined by the inadequately trained or experienced. It is exactly this that I keep discussing here. Your installation can be improved and is not to the 18th edition regulations, but even so could be quite reasonably described as requires improvement, a C3. A C2 or C1 needs more than non-compliance, it needs a fair level of risk that someone could be killed or injured by the defect. Such a defect, which has not been found in your case is an open circuit CPC because the primary level of protection is not reached, but as you have a 30mA RCD might not be considered immediately "Dangerous". The primary safety measure is "Automatic disconnection of supply" which should be achieved by your RCD, in exactly the same way as with a TT installation.


The idea above to change the light switch for a switched fused sput unit is reasonable and could be the first stage of improving your installation. The second would either to change the socket wiring to 4mm, to complete a ring circuit, or install a small CU with a 20 or 25A MCB for the socket circuits. Whilst doing this addition a 6A MCB for the lights might be the easiest solution for the lighting circuit. You may choose to add an RCD too, although the discrimination with the house might end up being a problem as I mentioned above. This could be sorted by adding an extra small CU, perhaps with a time-delayed RCD, or a non-RCD circuit to the existing CU, as RCD protection of the catenary is not a requirement unless the cable to it is buried less than 50mm in a wall, and is therefore not visible and reasonably protected from wall fixings.


You can see from this list that the corrections are not very onerous or difficult, and potentially need no work inside the house, depending on the various options you take. The outside works in the outbuilding would take a good electrician an hour or so, and 15 minutes to test fully a bit more if you change the cable size or make a ring, assuming the wiring is in mini trunking or clipped direct.


A good way to check if EICRs are reasonable is to pretend that the Inspector is charged with fraud because his EICR is too extreme and he wants the work to correct the installation. As this is criminal, the level of proof of his findings will be "beyond reasonable doubt", not the civil "the balance of probabilities". Each of his findings would be cross-examined using an Expert Witness for soundness, to show that they were fraudulent (or not). Remember that the Inspector has to show that they are fair, "beyond reasonable doubt". This reversal of the usual position that most Inspectors may fear is that they were not severe enough, because they doubt their own judgment and their ability to justify it. Surely this is a good test of competence?

The question of short circuit protection needs a reference to the adiabatic equation, where you will find the lighting circuit (even if 1mm2 cable) is safe from that point of view on a 32A Circuit breaker (presumably type B although you have not mentioned it). So it is very unlikely that even a short would cause the cable to fail, and even if it did due to some other defect the result is not catastrophic. To have a "Dangerous" or Potentially Dangerous" situation is not quite so easy as is often imagined by the inadequately trained or experienced. It is exactly this that I keep discussing here. Your installation can be improved and is not to the 18th edition regulations, but even so could be quite reasonably described as requires improvement, a C3. A C2 or C1 needs more than non-compliance, it needs a fair level of risk that someone could be killed or injured by the defect. Such a defect, which has not been found in your case is an open circuit CPC because the primary level of protection is not reached, but as you have a 30mA RCD might not be considered immediately "Dangerous". The primary safety measure is "Automatic disconnection of supply" which should be achieved by your RCD, in exactly the same way as with a TT installation.


The idea above to change the light switch for a switched fused sput unit is reasonable and could be the first stage of improving your installation. The second would either to change the socket wiring to 4mm, to complete a ring circuit, or install a small CU with a 20 or 25A MCB for the socket circuits. Whilst doing this addition a 6A MCB for the lights might be the easiest solution for the lighting circuit. You may choose to add an RCD too, although the discrimination with the house might end up being a problem as I mentioned above. This could be sorted by adding an extra small CU, perhaps with a time-delayed RCD, or a non-RCD circuit to the existing CU, as RCD protection of the catenary is not a requirement unless the cable to it is buried less than 50mm in a wall, and is therefore not visible and reasonably protected from wall fixings.


You can see from this list that the corrections are not very onerous or difficult, and potentially need no work inside the house, depending on the various options you take. The outside works in the outbuilding would take a good electrician an hour or so, and 15 minutes to test fully a bit more if you change the cable size or make a ring, assuming the wiring is in mini trunking or clipped direct.


A good way to check if EICRs are reasonable is to pretend that the Inspector is charged with fraud because his EICR is too extreme and he wants the work to correct the installation. As this is criminal, the level of proof of his findings will be "beyond reasonable doubt", not the civil "the balance of probabilities". Each of his findings would be cross-examined using an Expert Witness for soundness, to show that they were fraudulent (or not). Remember that the Inspector has to show that they are fair, "beyond reasonable doubt". This reversal of the usual position that most Inspectors may fear is that they were not severe enough, because they doubt their own judgment and their ability to justify it. Surely this is a good test of competence?