There is also the issue of disconnection times for line-neutral faults, for which an RCD will do absolutely nothing.
This is something I have questioned. Looking at 442.5 it seems we may need to have a 5 seconds disconnection time but that does not seem to be cut and dried.
In real terms a line - neutral fault can't really over stress the cables as the thermal part of the MCB will disconnect before insulation on the cables is overheated. The magnetic part is to ensure disconnection speed where the overload is 5, 10, or 20 times design current depending on if B, C, or D type.
The fact that a RCBO has a magnet trip incorporated would suggest time is still an issue.
It is easy to look at 543.1.3 without realising this whole section is on protective conductors so with an RCD is not really required.
With 411.3.2.2 NOTE 1: Disconnection is not required for protection against electric shock but may be required for other reasons,
such as protection against thermal effects.
NOTE 1: Where an RCD is used for earth fault protection the circuit should also incorporate an overcurrent protective device in
accordance with Chapter 43.
434.5.2 does seem to suggest as K is worked out for 5 seconds that the 5 seconds may apply to line - neutral faults.
The only thing which does seem to present a problem is spur length where the loop impedance is above the limit required to open the magnet part of the trip. 433.2.2 seems to limit spur length to 3 meters but it is by no means clear if this is dependent on the line - neutral impedance or not.
So I question where it states the line - neutral disconnection times need to be within a set time which would only be satisfied if the line - neutral impedance was within the limits needed to trip the magnetic part.
With B type RCBO's this does not really matter as the volt drop limits and the magnetic impedance required are nearly the same so we would of course measure the line - neutral impedance to ensure the volt drop is within limits.
But please do explain where time for line - neutral or line - line with three phase faults need to be within the time only afforded by using the magnetic part of the trip?