Poynting and Heaviside energy flow

Taken from: John D. Kraus, Electromagnetics, Fourth Edn., McGraw-Hill, New York, 1992

Inside (supeconducting) wires is E=0, because sigma->inf. J=sigma*E. "The electric field inside an ideal conductor will be zero when under static conditions. In this case, a current can flow without an electric field present inside the conductor. But this is only true for an ideal conductor, like a superconductor. "

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In a non-ideal conductor, such as a real world wire or metal plate, a small electric field is required to maintain a constant flow of current under constant potential. This is only true because the electric field, which is directly related to the electric force on the charges in the wire, must overcome the non-zero resistance of the wire."

Link here:https://physics.stackexchange.com/questions/388541/current-in-a-conductor/388888#388888