Current Density

Ohms Law? Drift Velocity? KCL ? KVL?

http://en.wikipedia.org/wiki/Speed_of_electricity

As the electric field is established across the conductors the electrons starts getting out of its mob mentality and starts moving in an orderly fashion. More is the field, better is the organisation (For example number of uniformed persons in a crowded train station or the number of traffic video surveillance and motorbikes/cars standing by the side in a highway waiting)

The speed of the individual electrons( equal to the drift velocity) remains constant but the more organised movement makes its effort felt. Secondly with the increased available energy level, especially in conductors, available number of electrons are easily increased (being pulled easily from the valence band) and that too helps in increasing the number of electrons (and hence current)

what happens when metal conductor melts due to heavy short circuit current?

I have located an excellent paper on this...

http://www.radioelectronicschool.net/files/downloads/howfast.pdf