The fire officer's report was essentially intended to identify "cause" (electrical fault). Whilst it made very interesting reading, and I am certainly not qualified to critique the report, I would suggest it may have misidentified the root or primary failure causation.
The report states :
6.3. The forensic examination of the distribution board shows evidence that there has been resistive heating on the connection between the two lower left hand side neutral bars that serve fuses numbered one to thirty six.
6.4. The affected connection was found to be considerably tighter than others on the same component and in comparison with those on the right hand neutral bar which serve fuses thirty seven to seventy two. This over tightening has caused a deformation of the wiring and over time caused the connection to loosen hence increasing the resistance of the wiring and subsequently the generation of considerable heat. This heating process has degraded the connection, including its insulation, continuously until full combustion (in the form of open flame) has occurred.
The report suggests that an overtightening caused failure of the connection. Unless such overtightening actually fractured wire strands then I fail to understand such a mechanism of failure.
Studying photographs DSC-0042 and DSC-0047 it is evident that the screws used to secure the main inter-connectors are "allen" screws whereas those the screws used to connect the outgoing load wiring uses "phillips" (or "pozidrive") screws. It is therefore to be expected that the failure point (allen screw) on the inter-connector would be "considerably tighter" than others (phillips) on the "same component". Further, thermal damage (melting) of the brass connector bar would possibly cause physical interference or fusion (brazing) onto the steel clamp screw and hence make it appear to be excessively tight.
Close examination of DSC-0047 clearly indicates a crack in the brass forming that part of the bar into which the inter-connector is clamped. This was mentioned by AL66, and is possibly the result of physical weakness of the bar due to the relatively thin wall thickness at the end of the brass bar. It is unlikely to have been caused by heat since this would simply have softened the brass and permitted plastic deformation. I would contend that the fracture either occurred during panel assembly (tightening of the inter-connector clamp screw) or at some later date, it not being unknown for brass under stress to fail at some later date - a phenomenon I've personally experienced.
Too often, in incident investigation, the need to identify cause fails to get to the root cause. In this case I submit that 'electrical fault' was a secondary cause of the incident and that the root cause is questionable design or assembly of the neutral connector bar. Unless, of course, the panel manufacturer specified inter-connector torque screw limitations which were then exceeded by the panel assembler.
