For the RCD work correctly you require a good earth return, with out this they are useless.

Earthing is essential and a good earth at that, in fact correct earthing is the most critical part of any electrical installation!

PLEASE DO NOT USE COPPER WATER PIPES ETC AS AN EARTH CONNECTION, this is very dangerous practice as in a fault condition these can and will become live and if you come in contact with them the current will travel via you to earth on it's journey back to the transformer in the street.

Actually ann ELCB, RCD or whatever will work with no ground whatever as it (as you say) measures the imbalance between live and neutral currents and assumes this is flowing to ground via a fault (you). An ELCB will NEVER save you if you decide to become part of the direct live-neutral circuit, you're just another load

Using a water pipe is definately NOT recommended, however, a somewhat iffy earth is far superior to NO earth. Do consider that in order to get a shock from the pipe (if the ELCB hasn't dropped or you don't have one [why not?]) you must be a better ground than the pipe. Unless your pipe has non-metallic elements or does not go anywhere near the ground this is unlikely.

If you absolutely must use a pipe then connect to it as close to the actual ground as possible (on the supply side of your meter, stop cock etc). Back in the dark old days, the incoming water main was always used as the earth, thank goodness we've moved on from then but it's still a reasonable substitute when combined with an ELCB.

BTW MEN means Multiple Earthed Neutral, sometimes called PME (Protective Multiple Earthing) in UK speak.

I'm surprised to see that fault currents can reach 6,000 Amperes before an 80 Ampere fuse has blown.

The source impedence from even a middle sized transformer is practically zero and the fuse takes a finite time to rupture, in that small time the current can grow to astronomical proportions, the fuse has to be able to break this fault current. If an arc gets sustained across the fuse then Houston, we have a problem.

Witness the explosive failure of small fuses, a 1A fuse will destroy itself with a large bang if (due to a fault) it gets the full weight of the mains behind it, that bang is the result of a lot more than 1A being interupted

Crossy, maybe this page can help to enlighten people about fault current? Sadly, most electricians worldwide do not understand the effects of fault current.

http://www.crossy.co.uk/wiring/breakers.html