Hi

Please have a look on the linked page below, you can see my questions there. Please help me with them. It would be kind of you.

page: http://img199.imageshack.us/img199/951/acdcgrounds.jpg

Regards
PG

 

It is quite often convenient or necessary for several DC supplies to share a common connection. Their current capacities may remain independent, but sometimes a load may be connected say from a +15V supply directly to -15V, when there would be some interaction.

AC sources can only be put in parallel safely if their amplitudes, frequencies and phases are suitably matched. Networks of parallel-connected AC sources of course form the basis of national power grid systems, but this requires some pretty serious electrical engineering to make it work. NB your circuit shows two sources in series, from the light bulb's point of view.

AC and DC grounds can sometimes be connected together, but in other circumstances they may need to be kept separate.