One of my favourite guides is: "in a satisfactory condition for continued use".  651.1.

Even if a consumer unit is all insulated, but is in good condition, I would add to it. People can  not afford unnecessary work and expense in many cases.

651.2 Note 2.

Z.

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.

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.

I'm with Zoomup. Your work has to be compliant as far as it can be. I would even say that it may be acceptable to add a circuit with no RCD protection at all. Let's not forget that BS 7671 is not mandatory. IMHO, "it's all I can afford" is a good reason for doing the best that you can under the circumstances.

What will come next? No new socket circuits unless they have AFDD protection?

What's all this about blinding? Surely the problem with a type AC RCD is that it may not trip with a pulsed DC fault.

Well the question was whether the new work would be compliant [ i.e. with BS 7671 amd2 ]. The answer is no. There are separate questions as to whether the work legally or morally should be complaint.

If installing a new socket in e.g. a HMO, then yes, that circuit now needs to be AFDD protected - in the same way that new sockets on an existing circuits need to be RCD protected one way or another.

I'm happy to defer to others about the whole blinding thing, but my understanding was that the sensitivity of type ACs could be reduced / eliminated by small DC currents.

My recent post about compatibility of Hager MCBs and an Efixx video has been viewed over a hundred times without anyone taking the plunge and commenting.

engx.theiet.org/.../are-hager-mtn-mcbs-backwards-compatible-with-hager-mt-mcbs

Chris Pearson said:

Let's not forget that BS 7671 is not mandatory.

Not the case if you have Solar PV or other form of generation that operates in parallel with the DNO network, although this will kick off the rabbit hole of "which version of BS 7671, because the legislation says ..." even though this has been run many times before.

Still, it's true to say that, at least right this minute, there's no need to use BS 7671:2018+A2:2022 (but you can if you want).

You now have some replies ... probably what you'd expect to see, though, at least from me!

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.