For safety reasons, the melting bath in a crucible induction furnace should be continually earthed. This earthing is as a rule provided by bottom electrodes. In the case of ceramically lined furnaces, this is no problem. When using crucibles of graphite clay or silicon carbide, a spiral of St 4828 in graphite is embedded beneath the crucible and connected to earth potential outside the furnace housing.
Another method is earthing by means of the casting spout, in which is a shackle which is welded on one side to the steel construction. With the 1st casting from a crucible, the molten metal flows over the shackle, and the bath is then earthed via the con- ducting crucible. Lost tamping forms have as a rule no connection with the bot- tom electrodes during the sintering charge, since the crucible bottom is tamped 5- 10 mm higher than the bottom electrodes. In order to ensure earthing in this case, the earthing between the form and earth can be created with the aid of an earth cable with 2 contact magnets, in the same way as for arc welding.