Yes, TT has been employed for a considerable time, using protection in the form of an ELCB (Earth Leakage Circuit Breaker).
There were early types of current-balance ELCBs, which would trip on an imbalance of about 500mA or so. In more recent times these were made more sensitive, and until a few years ago 100mA was pretty much the norm. These days, 30mA is considered standard, so they still don't offer quite the same level of protection as the typical American GFCI. As the typical device now feeds an entire house, any attempt to increase sensitivity further would lead to problems of nuisance tripping.
The committees here have an unfortunate habit of messing around with terminology for no particular reason, and the current-operated ELCB has been renamed twice in comparatively recent times. First it became an RCCB (Residual Current Circuit Breaker), then more recently still the name was changed to RCD (Residual Current Device). At least one manucturer appears to have resisted this latest change and still uses RCCB on some products.
We also had a device known as a voltage-operated ELCB, which inserted a solenoid trip coil
between the house grounding and the local rod.
These devices are obsolete now, but were very common in rural residential properties up until the 1970s. There are still quite a lot in service in my area.
Click here to see how they were wired. [This message has been edited by pauluk (edited 08-29-2003).]
