BS7671 requires us to comment and apply codes for instances which are dangerous, or potentially dangerous.
There is no requirement to comment or apply a code for instances which are neither dangerous or potentially dangerous.
Code C3 should be used for instances which are neither dangerous or potentially dangerous, but where improvement would enhance safety.
I and many others, use code C3 for instances which would have complied with the then current Regulations at the time of design/construction, but do not comply now. Not strictly in keeping with the requirements, but then the same could be said in respect of the reasons given in BS7671 for apply the code C3.
As for commenting and applying a code for a wooden backed CU.
This is something that the NICEIC have been advocating for many years. There is nothing in BS7671 which suggests that such CUs should be condemmed.
Ironic that the plastic CUs that the NICEIC have opted to use to replace the wooden backed boards are now to be banned in domestic installations.
Then of course there's the fact that fire doors are made from wood.
With regards to the cooker control switch, I would apply a code C2, as it is possible that the switch could be damaged by heat.
Someone mentioned that in the event of a chip pan fire, it would not be possible to reach the switch because of the flames.
Normal cooker control switches do not comply with the requirements for emergency switching.
As such there is no requirement to take into consideration the fact that flames from a chip pan fire would prevent the switch from being used for emergency switching.
I think the definition of a circuit has been more than adequately covered.
It may be that haveing what would normally be considered as 2 or 3 circuits connected to a single OCPD, would not be good workmanship, or minimising inconvenience in the event of a fault.
Undersized main earth would be a C2, if the CSA does not satisfy the adiabatic equation, C3, if PME conditions apply and there are no signes of damage due to overheating.
