Would a surge protector (on an RCD) circuit protect from a lost neutral overvoltage? I know that isn't the aim of them (transient spikes only rather than sustained overvoltage) but I am thinking it may be possible (although very alarming if there isn't a thermal fuse in the surge protector). This is referring to a single phase TN-C-S installation. If the neutral is lost, the line voltage will float. The surge protector's MOVs theoretically would start to conduct. That is of course making the assumption that the floating voltage goes above the clamping voltage of the MOVs. I would assume that if there was a persistent current flow through the MOVs (to ground) that the MOVs would burn out very quickly (or rather explode or catch fire unless they have a thermal fuse). If the MOVs are shunting the current to earth for over 30ms, I would assume the RCD would trip due to the L-N inbalance which now exists. If that is correct, then hopefully the elevated voltages won't last for very long and the potential for damage to occur (from both the voltage and the now orange hot MOVs) be very small on every RCD protected circuit. The non-RCD circuits are pretty much stuffed. On another tangent, it is well worth checking that any surge protector you buy does have a thermal fuse. Bigclive did a teardown of one and there was no thermal fuse. Given how MOVs behave when they fail, it is well worth checking if it's possible to open the case. It's completely irresponsible of manufacturers to skimp on thermal fuses in what is essentially a time-triggered incendiary bomb encased in flammable plastic. Given the influx of deathdaptors, exploding fake chargers, thin conductors in 10A cables and all the other dangerous tat out there, it's not surprising in the least. I wonder how many fires surge protectors (even those with thermal fuses) have caused. I wouldn't trust the plastic to be fire retardant either. If they skimp on a thermal fuse, the plastic is going to be the same.