I've always felt its a bucket with holes filling more buckets with holes (although I'm prepared to stand corrected as i don't have anything to do with domestic, so this is just my uneducated musings)
Part P includes notification of new circuits right?
When is a new circuit not a new circuit?
Say a redundant 16a radial in 2.5 to a single 20a DP switch is found in an airing cupboard. A competent homeowner decides to remove the DP switch, install a single socket, then extends this to 3 more sockets with more 2.5 in an adjacent room, creating a radial socket circuit.
It's not a new circuit - the run from MCB to first point was already there after all right? So I would assume its non notifiable - but the characteristics are significantly different.
Yet if someone were to run a new 2.5 radial from source of the same design, it would then become a new circuit? It's literally that one original length from MCB to first point making it an "existing circuit".
I'd say the addition of those extra sockets to an "existing circuit" leaves far more room for error than, say, adding a single PIR operated light next to the DB from a new, dedicated 6a MCB - but that would be classed as a new circuit and notifiable - despite being a far simpler task
Oh but hang on - what about if a new PIR light was installed next to the DB but instead of being fed from a new dedicated 6a MCB, was just fed directly from the output of an existing lighting circuit 6a MCB? It's not a new circuit - it's fed from the same MCB as an existing circuit, so it's just an addition to that circuit surely and wouldn't require notification?!
Why on earth would the latter be non notifiable, but the former would be ?
Take also replacement of damaged lengths of cable - I believe this is actually specified on some LABC guidance I read somewhere as being a reasonably acceptable DIY task. Example:
Homeowner drills through an out of zone RFC 2.5 cable between two socket outlets (Lets say its an RFC just feeding that room). Its in old colours. He pops to Wilko, buys a few metres of new 2021 date stamped 2.5 and proceeds to replace the damaged section and puts it in zone in the process. Sounds reasonable right?
Let's say instead he drills through both legs of the ring after they leave the DB . So he replaces both legs from the MCB to the first and last socket, with his 2021 embossed 2.5, leaving the main part of the ring intact.
It's not a new circuit - but would an inspector raise questions on seeing the new cable leaving the DB?
Sorry- I've clearly thought about this too much. Waiting to be corrected gladly.