1-) Why do sparks exist when we make touch the (+) line to the (-) 
line of
dc voltage or (phase and neutral line of AC)?

Heated/vapourised material from conductors.

2-) Where is the source of scent after touching the two lines to each 
other?

Ozone - oxygen in air changed from O2 to O3. Also possibnly material 
from heated conductors or insulation.

3-) (Although this one is a bit foolish question) Is it wiser to test 
the
existance of the electricity on the AC line by letting touched phase 
and
neutral lines?

No!!!

ie Neutral won't tell you anything IF it is properly functioning and 
may turn out to be as lethal as Phase if things are not as they should 
be. use a meter !!!!!!!!!!!!!!!!!!!!!!!!!!!!


        Russell McMahon

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