THERMALLY PROTECTED SERIES INTRODUCTION The Thermally Protected Series is designed for safe disconnection of the varistor from the circuit due to abnormal operating conditions. These components consist of 2 or 3 leaded wire leads, a thermal disconnect (FN, FM, FN), and have nominal diameters of 14mm, 20mm, and 25mm. Fusible link designs (FF, FT) are also available. STYLE DESIGNATION The Maida Style Number is the typical means to identify our components when ordered. The style number identifies.