James,
When you say the neutral bar, I take it you mean the busbar in the distribution panel. You definitely would not connect to the neutral bar in the panel.
The whole principle behind using the RCD is that a fault current will cause an imbalance between phase and neutral currents. If you made the connection you suggest, then any fault current on the protective circuit conductors would be returning through the neutral side of the RCD, and there would be no imbalance to trip it.
The clue to the connection arrangement is given by the second letter of the "TT" designation. It means that the earthing is to a local earth only (T = terre, French for earth). If you earth to the neutral, then it is no longer a TT system.
If you really could not obtain a sufficiently low earth impedance to use TT (unlikely with modern RCDs), then you could convert to TN-C-S, otherwise known as PME.
In this case, the earth bar in the panel would be earthed to the incoming supply neutral ahead of the meter. This would, of course, need appropriate provision from the power company and require all the extra bonding requirements for a PME system.
In the early days, it was precisely the problem of high earth impedance values in certain areas which led to PME being used. Remember that this was when TT protection was generally by voltage and 500mA current-balance ELCBs, not the 30 and 100mA RCDs of today.
Qualifier:
Everything stated here applies to the wiring in the U.K. only. The precise arrangement of earthing is something which varies considerably from country to country.
[This message has been edited by pauluk (edited 04-10-2005).]
