watch these pics:

Notice that they are not at the same time.
so my question is: what does the "temporally ground" thingy does?
u wont get shocked anyways... :S

 

Those pictures didn't come from our book I don't think. The second one is incorrect, the brown dude is a dead man if the second switch is open. If it is closed there lots of fire and smoke, as the power source is shorted. The second switch and load are irrelevant.

In the first illustration is either switch is closed the other dude is dead, and if both are closed the third guy's a gonner. He ain't gonna be too happy anyhow, as he is shocked in two of three scenarios.

 

Those pictures didn't come from our book I don't think. The second one is incorrect, the brown dude is a dead man if the second switch is open. If it is closed there lots of fire and smoke, as the power source is shorted. The second switch and load are irrelevant.

In the first illustration is either switch is closed the other dude is dead, and if both are closed the third guy's a gonner. He ain't gonna be too happy anyhow, as he is shocked in two of three scenarios.

ok, i think i got it. Green and brown are dead.
but dont u think that the "temporary short wire" is NOT necessary?

btw i got this pic from :http://www.allaboutcircuits.com/vol_1/chpt_3/5.html
and i painted those dudes cuz i got confuse with that "electrical common" and "temporary ground" things.
thx a lot for help!

 

Basically a load to ground with the power disconnected is equivalent to ground, the resistor is going to that point.

In many ways this all applies to ESD control too, there are a lot of similar concepts.