The Particular protection unit mentioned will also protect against a voltage surge between the line and neutral. In Cases like that it will act as a short circuit causing the breaker to trip.
You would want to mount the unit in the area where you can occasionally glance at it to confirm is still working. As the LED will illuminate if it is still functioning.
We can also buy test plugs that have 3 lights on them so you can test the supply by putting the tester plug in the wall socket or extension lead etc, any one can buy them and I also have a Volt pen that you just have to put near the wall or socket to see if there is power there or not, I like having this stuff because I have often worked in places where the power was meant to have been switched off only to find old wiring from the 1900s that was still live,
It's a shame all our plugs are not the same because it would save a lot of worries having the right gear to check out a supply before you hook in to it.
Here you can also buy an RCD Protection doodad that you plug in to the wall and then plug you Item/Power Tool etc in to it, Over here you can't use 240V tools on a building site without using one of them, But the standard Building Site power tools are 110v which are plugged in to a 110v Transformer that weight about 30+LBS and then the transformer is plugged in to the 240v. and all Copper piping on sinks Baths and showers have to be earthed also. as do metal bathtubs etc and Campers and Caravans/Camping Trailers are also earthed. they are nuts about it but it is almost impossible to get a shock over here unless you do it on purpose.