An electric furnace is any of various industrial furnaces heated electrically to very high temperatures. In an arc furnace, batches of steel are melted by the heat of electric arcs struck between graphite electrodes and the charge. In induction furnaces, used mainly for remelting batches of steel, a refractory crucible is surrounded by a large water-cooled copper coil. When this is connected to a high-frequency AC supply, eddy currents are induced in the batch which heat it. Often a lower-frequency field is also applied to help stir the charge. Chamber furnaces are simply large electric ovens, heated from the walls.