Abstract: An isolation transformer for connection between a source of alternating current power and electrical components, the operation of which components is affected by voltage excursions occasioned by electromagnetic pulses. The transformer includes a ferromagnetic core including first and second ends and at least two legs extending between the ends and defining therewith at least one window in the core. Also included are a primary coil surrounding a first portion of the core and extending through a window in the core, and a secondary coil, spaced from the primary, surrounding a second portion of the core and extending through a window in the core. A metallic isolation shield is positioned between the coils with the shield having core apertures for receiving components of the core so that the shield passes through each window of the core. A first metallic housing is mounted on the shield and has an opening for receiving the primary coil and the portion of the core on the primary coil side of the shield.