To put it more simply: if the phase is wrong, the effect is the same as a short circuit, which fuses and circuit breakers protect against. If the frequency is wrong, the phase will become wrong after a number of cycles.
> There isn't really any practical way to prevent overvoltage though. So a rogue controller in charge of all the solar systems in a street might be able to do quite a lot of damage to consumer devices.
There is, it's called a surge protector or surge protective device (SPD). It converts any overvoltage above a certain level into a short to ground, which then trips the fuse or circuit breaker. It's often used as a protection against lightning-induced currents.
> A problem from the utility point of view is that they can no longer guarantee that the 240 V side of the distribution system is safe to work on just by tripping a breaker on either side of the distribution transformer. So all work on the 240 V distribution system has to be done with the assumption that the system is live.
From what I've seen, the utility workers usually ground the wiring when working on it (they have a special-purpose device for that). Once it's safely connected to ground, it's no longer live.
