change of mcb to rcd

[JohnW2]

TTC calls it 'only Additional Protection' ('additional' to what, I would have to ask, in that situation).

As detailed in 410.3.2 and Section 415 of the BGB ... Additional protection provided by and RCD ... "....use of RCDs as addition to basic and/or fault protection"

Yes, I agree that is literally true - it does say "basic and/or fault protection". However, the 'basic protection' (insulation, enclosures etc.) is so 'basic' (and so inevitably present), that I imagine most people think of 'Additional Protection' as meaning 'in addition to primary fault protection' - which becomes essentially meanless with TT, since an RCD/RCBO is the only possible (hence not, in usual parlance, 'additional' to anything) effective fault protection.

In any event, my original point stands - that your statement that an RCD in the OP's house would be there "to provide basic protection, not Additional Protection" is not consistent with the language of Chapter 41 of the regs or the regs' definition of 'basic protection'.

Kind Regards, John