And the above is basically why, the UK has crap TT systems and always will do, with the perpetuation of some of the stupid comments such as these two examples...
200 ohms from a 1m rod is about as useful as using a bent screwdriver to tighten a screw, be it for the Ra or it's stability! The UK's obsession with this crazy figure of 200ohms (which is based only on stability) is about as far from logical as you can get. No other country that i know of, has or mentions such a high limit, of anywhere approaching that figure. Yet both of you are trying to defend it!! It is indefensible and that section of the Reg's is in dire need of a revision. ...In fact there was talk of a lowered figure being pushed for inclusion into the last batch of amendments...
No-ones trying to obtain disconnection times equal to a TN system, but that's not by any means an impossibility either. But the lower an Ra is, the better the chances of having a protective device trip in a relatively decent enough time, not to cause fire or maybe possible injury, despite a non-functioning cure-all RCD... Great if you have parallel earths from water/gas bonding to help you along, well until they come along and replace with plastic that is...
And yes your quite right, RCD's DO fail and a lot more often than either of you will, or care to admit too. Just because YOU haven't read anything about an RCD causing fire, injury or even a death, doesn't mean it hasn't happened, can't happen, won't or will happen!! Smugness like this, just doesn't become you!!!
What a sorry state the UK TT systems are these day's, ...in the past it was nothing to find many if not most old TT systems with Ra's 5 ohms or lower, even 10 ohms was considered to be on the high side, (even the Yanks talk about trying to improve a 20 ohm Ra with an additional Rod!!) Yet here we are talking in the realms of 200 ohms, and even experienced electricians trying to defend this as all fine and dandy. Why, because we now have the cure-all RCD devices, Oh, ...and it's written in there all seeing all knowing bible, so it must be good-un!! ...lol!!