Doesn't the fact that the 32A tripped indicate that it must be 'faulty' and over-sensitive rather than it being surprising that the other devices 'failed' to operate?
I don't really understand. Until some other device operated (or the fault self-terminated), there would be a very high current (>>32A) flowing through the MCB - so why do you think the MCB would be 'wrong' to operate? As below, are you perhaps (incorrectly) assuming that the fault current will rise gradually, rather than be very high (>>32A) from the outset?
I don't quite understand why so many thought the 32A would trip before the 16A.
Nor do I. In the face of a very high fault current, I would expect it to be fairly random as to which operated first - but I can't think of
any reason for suspecting that it would be more likely for the 32A one to trip first.
The fact that the 10A and 16A survived is, surely, how it should be.
In a perfect world, only the device with the lowest In would operate - but that obviously is not 'how it happens'. Such discrimination would mean that devices would be required only to trip if the fault current persisted for longer than the disconnection time (for same current) of any device with a lower In. There is no such requirement, and nor would it be practical/realistic to have such a requirement.
My comments regarding the 30A causing the 5A fuse to blow 'instantly' (whilst not being enough to operate the MCB and mcb part of RCBO) was because, perhaps misguidedly, of the cable being cut which may not immediately result in a full short circuit.
It sounds as if you were invoking something analagous to the 'classic misconception' about RCDs - i.e. the belief that a 30 mA RCD
limits L-E fault current (e.g. through a person) to 30 mA. As you know, that would only be the case if there were a gradually increasing current - whereas, in reality, the 'full current' (determined only by Ohm's Law) will flow 'immediately' (and continue until the device operates). In present context, you seem to be assuming a gradually increasing current due to the L-N fault, such that device with the lowest In will operate before the current even rises to high enough to operate any of the others. That obviously is not how it is. An L-N fault will result in an 'immediate' fault current (usually of a few hundred amps) flowing through all of the protective devices, not a gradually increasing fault current. Which device operates first will be entirely dependent upon the operating characteristics of those devices (when 'a few hundreds of amps' is flowing through all of them).
Also note my recent comment that the sort of fault we've been discussing is somewhat atypical, in that it quite possibly persisted for only milliseconds before 'self-clearing'. That has the potential to alter everything.
Kind Regards, John