In belgium we have a TT system (in residential installations) and therefore use type C curve.
Even if you use a TT system, you must have something to protect the .75 mm2 lamp cords from short-circuit? (A 20A type C breaker will allow 100A current for several seconds. There won't be a trace left of the lamp cord by then...)
Some people might be wondering what TT and TN has to do with tripping curves of breakers. I'll attempt to explain it. In a TT system, there is no connection between earth and neutral. The Protective Earth is only connected to a ground rod. The resistance of this is too large to allow a short-circuit to ground. (With a 25 ohm ground rod, the current will only be 230V/25ohm = 10A.) Therefore, these systems always have an RCD (GFI), in the 100-500 mA range which cuts the power in case of a ground fault. Even if a time delay RCD is used for this, the response time is short enough to prevent the dangerously high voltage on metal objects connected to the protective earth present during a fault condition from killing someone.
In a TN system, there is a connection between neutral and earth. If there is short-circuit between live and earth, the current will be high enough to trip a breaker. For this reason, these systems don't need to be equipped with an over-all RCD. However, care must be taken that the fault current is high enough to trip the breaker within a short period of time (no more than 5 seconds). To check this, you do an earth loop resistance calculation and sometimes also test it once you have made the actual wiring. A fast breaker (type B) will allow a higher resistance than a slow-blow (type C), and hence longer runs.
If you can't get a low enough resistance, you need to install an RCD, just like in the TT system.
[This message has been edited by C-H (edited 10-14-2002).]
