A method of determining the location of a fault within a first inductive part of a DC electrical circuit, where the DC electrical circuit comprises a voltage source, the first inductive part and a second inductive part and a shortened circuit of the electrical circuit created by the fault comprises the voltage source, a portion of the first inductive part and the second inductive part, all connected in series, and where further the fault occurs across first and second points in the first inductive part, the length of first inductive part between a positive terminal of the voltage source and the first point being substantially equal to the length of first inductive part between a negative terminal of the voltage source and the second point, and where further the voltage source supplies a known voltage V s at the time the fault occurs and the second inductive part has a known inductance L 2 at the time the fault occurs, the method comprising the steps of: i) determining a voltage V 2 across the second inductive part immediately after the fault occurs; ii) equating the ratio of V 2 to V s with the ratio of L 2 to L 2 + an unknown inductance L 1s of the portion of the first inductive part in the shortened circuit; iii) determining the length l 1s of the portion of the first inductive part by either: a) expressing L 1s in the equation of ii) as a proportion n s of a known inductance L 1 of the first inductive part, solving for n s and, given that the first inductive part is known to have a linear inductance to length relationship, equating n s with the ratio of l 1s to a known length l 1 of the first inductive part and solving for l 1s; or b) solving for L 1s in the equation of ii) and given that the first inductive part is known to have a linear inductance to length relationship, equating the ratio of L 1s to a known inductance L 1 of the first inductive part with the ratio of l 1s to a known length l 1 of the first inductive part and solving for l 1s; and iv) inferring the location of the fault as occurring at the position along the electrical circuit at which 1 2 l 1 s is exhausted when starting from either of the positive and negative terminals (52, 54). i) determining a voltage V 2 across the second inductive part immediately after the fault occurs; ii) equating the ratio of V 2 to V s with the ratio of L 2 to L 2 + an unknown inductance L 1s of the portion of the first inductive part in the shortened circuit; iii) determining the length l 1s of the portion of the first inductive part by either: a) expressing L 1s in the equation of ii) as a proportion n s of a known inductance L 1 of the first inductive part, solving for n s and, given that the first inductive part is known to have a linear inductance to length relationship, equating n s with the ratio of l 1s to a known length l 1 of the first inductive part and solving for l 1s; or b) solving for L 1s in the equation of ii) and given that the first inductive part is known to have a linear inductance to length relationship, equating the ratio of L 1s to a known inductance L 1 of the first inductive part with the ratio of l 1s to a known length l 1 of the first inductive part and solving for l 1s; and a) expressing L 1s in the equation of ii) as a proportion n s of a known inductance L 1 of the first inductive part, solving for n s and, given that the first inductive part is known to have a linear inductance to length relationship, equating n s with the ratio of l 1s to a known length l 1 of the first inductive part and solving for l 1s; or b) solving for L 1s in the equation of ii) and given that the first inductive part is known to have a linear inductance to length relationship, equating the ratio of L 1s to a known inductance L 1 of the first inductive part with the ratio of l 1s to a known length l 1 of the first inductive part and solving for l 1s; and iv) inferring the location of the fault as occurring at the position along the electrical circuit at which 1 2 l 1 s is exhausted when starting from either of the positive and negative terminals (52, 54).