I seem to remember that the E field is the gradient of the potential... Of course you will need far more than this for the current density as current density also depends on the frequency. At higher frequencies the current is confined to the surface of the conductor (google skin effect)

Guest,

I am not clear as to what you wish to achieve.

Normally, current density (DC or Frequency low enough for skin effect to be ignored) would equate to current flow divided by the cross sectional arae of the conductor.

Sleepy

Guest,

Perhaps this link will help you out.

and Wiki.

Maybe I make it simple.

e.g.

the cross sectional area of 400A cable is 180mm2, can I calculate the current density by 400A / 180mm2 = 2.22mm2 ?

Besides, could anyone proivde the list of acceptable current density of different rating of conductor? the rating of conductor is 100A, 200A, 400A, 600A, 800A ..........