This paper discusses the increasing requirements for an effective means of controlling fault levels on electrical networks and describes the work by Rolls-Royce and partners to develop a practical superconducting fault current limiter. Practical superconducting fault current limiters require materials with a high tolerance to mechanical process handling and must be sufficiently robust not to be damaged by the severe electro-magnetic and thermal stresses imposed when restricting a fault current. Magnesium diboride (MgB 2 ) is amongst the most promising materials under consideration for superconducting fault current limiters. This paper reports tests which have been carried out on several MgB 2 round wire samples wound with small bend diameters. Electrical characteristics and fault current limiting abilities were determined of a number of MgB2 samples when cooled to below their critical temperature. During these tests strong and repeatable current limiting properties were observed for 50Hz ac applications. Furthermore, MgB 2 exhibited unusually high tolerance to mechanical process handling, clearly differentiating itself from other superconducting materials.