A portable circuit interrupting apparatus for use in association with a circuit isolating device such as a fuse cutout, disconnecting switch, or power fuse. The apparatus comprises a tubular housing, with a sleeve coaxially and slidably mounted within the housing. A ring engaging terminal is mounted to the housing and is adapted to engage a ring-like conducting part of the isolating device, and a hook engaging terminal is mounted to the sleeve and is adapted to engage a hook-like conducting part of the isolating device. The ring engaging terminal is mounted to the housing by means of a tubular cylinder fixed to the housing, and a shuttle slidably mounted in the tubular cylinder and so as to be lockable in each of at least two axially spaced apart positions, and the ring engaging terminal is fixed to the shuttle. A shunting circuit is connected between the ring engaging and the hook engaging terminal and includes a circuit segment positioned within the housing which is automatically interrupted upon the sleeve being moved to a withdrawn position.