Electric earthing switch for a gas insulated substation, to connect at least one line conductor of the substation to the earth, this earthing switch comprising: - a metallic housing delimiting an inner compartment and an outer compartment and comprising a flange delimiting a single main opening of this housing which communicates with the inner compartment; - an insulating plate to be located and tightened between the flange of the housing and a flange of a compartment of the substation enclosing each line conductor; - at least one line contact (3a, 3b, 3c) carried by the insulating plate and having an insert portion (6a, 6b, 6c) with a thread bolt (7a, 7b, 7c) passing through the insulating plate to be electrically connected to a line conductor; - at least one fixed earth contact (8a, 8b, 8c) passing through the wall of the housing and secured to this housing, this fixed earth contact having an outer portion out of the housing and an inner portion located in the housing; - at least one sliding earth contact (9a, 9b, 9c) carried by the inner portion of a fixed earth contact (8a, 8b, 8c) and sliding relatively to this fixed earth contact (8a, 8b, 8c), each sliding earth contact (9a, 9b, 9c) being electrically connected to this fixed earth contact (8a, 8b, 8c); - an actuating mechanism to move every sliding earth contact (9a, 9b, 9c) between an open position at a distance from the line contact (3a, 3b, 3c) and a closed position in electric contact with the line contact (3a, 3b, 3c); - each fixed earth contact (8a, 8b, 8c) extending perpendicular to the sliding direction of the sliding earth contacts (9a, 9b, 9c); - and wherein the sliding contacts (9a, 9b, 9c) and the actuating mechanism are enclosed in the inner compartment, the outer compartment being dedicated to a drive actuator to be connected to the actuating mechanism. - a metallic housing delimiting an inner compartment and an outer compartment and comprising a flange delimiting a single main opening of this housing which communicates with the inner compartment; - an insulating plate to be located and tightened between the flange of the housing and a flange of a compartment of the substation enclosing each line conductor; - at least one line contact (3a, 3b, 3c) carried by the insulating plate and having an insert portion (6a, 6b, 6c) with a thread bolt (7a, 7b, 7c) passing through the insulating plate to be electrically connected to a line conductor; - at least one fixed earth contact (8a, 8b, 8c) passing through the wall of the housing and secured to this housing, this fixed earth contact having an outer portion out of the housing and an inner portion located in the housing; - at least one sliding earth contact (9a, 9b, 9c) carried by the inner portion of a fixed earth contact (8a, 8b, 8c) and sliding relatively to this fixed earth contact (8a, 8b, 8c), each sliding earth contact (9a, 9b, 9c) being electrically connected to this fixed earth contact (8a, 8b, 8c); - an actuating mechanism to move every sliding earth contact (9a, 9b, 9c) between an open position at a distance from the line contact (3a, 3b, 3c) and a closed position in electric contact with the line contact (3a, 3b, 3c); - each fixed earth contact (8a, 8b, 8c) extending perpendicular to the sliding direction of the sliding earth contacts (9a, 9b, 9c); - and wherein the sliding contacts (9a, 9b, 9c) and the actuating mechanism are enclosed in the inner compartment, the outer compartment being dedicated to a drive actuator to be connected to the actuating mechanism.