Abstract: An induction furnace intended for melting a metal which is disposed in a crucible in an alternating magnetic field developed by an inductor enveloping this crucible. Induced in the metal is a current which heats the latter. Fixedly mounted intermediate the crucible and the inductor on the outer surface of the latter is a heat-resistant current-conducting screen made from a carbon material of not more than 1.5 mm thick. The screen envelops the entire inner surface of the inductor and is electrically connected to a signal system intended to indicate the degree of wear of the crucible wall. The signal system is set to a predetermined voltage at which the furnace is shut down to avoid an emergency situation.As the crucible walls wear out in the course of operation, the crucible resistance is therefore reduced, whereas the electrical potential in the crucible between the screen and metal is increased.When a preset voltage is attained, the signal system is actuated to discontinue the furnace operation.