"Can you elaborate on this? You've got me trying to imagine what kinds of domestic DIY wiring faults could cause problems further back in the system."
While I don't know how common it may be down under; I know up here (it feels strange to say that in Florida) in hurricane country, we have some dodgy generator instalations that could back feed into the network. I know that a residential generator would trip out if it tried to power a large part of the network but, it could be a hazard, to a linesman, in an isolated setting.
