wires coming from the light switching points to a central place in the fuse boxes.
Those light switches will, when pressed, close a low voltage circuit ( scheme: +5V -> resistor -> switch -> ground).
contradictory, please clarify

However, I've been told that this is a 'dangerous' setup. Not dangerous for human beings (since it's all low level voltage), but for the circuitry itself.
I have "blown" several "electronic" telephones that way, but that is a lot more wire.

1. How big is the influence of induction on the wires with the situations given (thunderstorms, lightings,...)?
somewhere between nothing and a lot

2. Can those long wires be put in the neighborhood of normal voltage wires (e.g. 220V for Europe)?
If twisted pair, I do not see why not: however PLEASE make sure no short between the two can happen

3. What can be done to prevent the electronics from being damaged?
RC or, better, LC circuits

4. Is it wise to use twisted pair wires to overcome the 'long' distance (let's say, max. of 15 meter)? For instance, to reduce the influence of other disturbances (e.g. a fan or raiser which is active)?
yes, then the problem is not signal, but common mode

5. Should those wires be shielded? I'm planing to use UTP for the connecting wires between the switches and the electronic hardware. Should I use FTP or UTP?
Shielding twisted pairs will help common mode, it has no effect on signal

I have, in several instances used RS485 interfaces to simply carry an on/off signal. These chips come in versions with a very high voltage surge resistance.
http://para.maxim-ic.com/compare.a...ce.cfm&ln= show several that can withstand 15kV. Also the low differential termination cut the noise a lot.


if what you are trying is home powerline communication have a look at
http://www.maxim-ic.com/homeplug.cfm

Erik