My first thought was like you all point out that its a bad neutral connection, somewhere between the cellar and the third floor.
Let me explain to you why I dont think that its a neutral fault:
When I disconnected the Neutral feeding the rcd 30mA, then the fault went away. i.e. 230v phase to N and 0v N to Earth.
This RCD is only part of the panel (on 3rd floor), which means that when I disconnected it the rest of the panel was connected with all the loads on it. So the fault is clearly somewhere after the RCD 30mA and not in the Neutral from the cellar to 3rd floor.
Maybe one of the RCDs( under-rated at 40A ) has over-heated and done something weird.
That's possible, but how does it explain this fault even if the RCD30mA is burnt?
Please let us know how you get on with this problem Belgian, because we're all dying to know the outcome.
The thing is that this problem isn't there anymore after I turned of all the breakers which are placed ater the RCD 30mA and switched it back on. Firthermore after having explained to this client that they would need to change both RCDs since they are under rated, after having heard the price of both rcds 63A, the client said that they will "have to think it over", which most probably means that since everything is working now, they dont want to make any expenses.
[This message has been edited by Belgian (edited 05-24-2005).]
