If the new circuit requires a type A (e.g. because it has sockets or a known load with electronic components) then protecting it with a type AC isn't compliant with BS 7671 amd2 - there's no leeway there. On the other hand, being plastic is not an issue.

But if an appliance becomes faulty with an earth fault, unless the system is TT, the overcurrent protective device will still disconnect the faulty appliance.

Z.

But if an appliance becomes faulty with an earth fault, unless the system is TT, the overcurrent protective device will still disconnect the faulty appliance.

Z.

So? Normally RCDs are required for additional protection rather than fault protection. A nail in the wall contacting just the L conductor won't cause an overcurrent, but may still kill you if you touch it, unless an RCD trips. And hopefully that RCD isn't being blinded by DC leaks or faults.

Banging a nail into unknown territory is stupid. It is just like tombstoning, i.e. jumping into unknown water that may have hidden dangers. Fatality by banging the nail into a wall and connecting with a line conductor MAY kill somebody, but largely depends upon how well they are earthed. Probably if they are standing on an insulating wooden floor or carpet they will just get a reminder of how stupid they have been. There are not many reported deaths regarding this scenario.

SOLUTION. Don't bang nails into walls that may contain pipes or cables.

Z.

You seem to be saying that we don't need to install RCDs for additional protection as only stupid people would be killed by their lack?

This demonstrates the need not to drive nails into unknown  territory where there may be concealed pipes or cables. That is like tombstoning, diving into unknown water with possible hidden dangers.

Solution. Don't bang nails into walls. The regulations can't protect idiots against ALL stupid actions.

Anyway, if the nail banger is standing on an insulating wooden floor or dry carpet the shock would not be fatal in most cases. How many reported nail banging deaths do we hear about?

"B.S. 7671 contains requirements for the design, erection and verification of electrical installations as to provide safety and proper functioning for the INTENDED USE." 120.1.

This does not include damage to fixed wiring by vandal nail bashers.

Z.