Chucking stuff in is close to the truth. In research furnaces they lob bin bags full of various materials they want to add to the cast depending on the grade o

Chucking stuff in is close to the truth. In research furnaces they lob bin bags full of various materials they want to add to the cast depending on the grade of steel they're trying to produce. The whole bag goes in, the plastic is negligible. Often these things are heated (at least initially) with big ole' electrodes or by using induction. Nominal current is in the kiloAmperes. No pacemakers please! To put it into perspective (again), most steel plants have their own dedicated power stations on-site.