a high speed actuating mechanism for operating the contacts of a circuit interrupter has an operating shaft connected to the contacts and to an operating piston . the operating piston has a short - circuited conductive ring or repulsion disc which is closely coupled to a lenz coil operator in one position of the actuating mechanism . the operating piston also has an enlarged diameter sealing protrusion which seals against an annular seal which is concentric with the lenz coil operator . both the lenz coil and the sealing ring are spring - mounted to have several degrees of resiliency to enable proper relative location of the repulsion disc and the lenz coil and proper relative location of the annular seal and contact protrusion to control seal penetration and to enable compensation for contact erosion when butt - type contacts are used .