The paper presents the method for determination of ground fault current distribution in the cases when feeding cable lines are passing through urban and/or suburban areas, or when many relevant data are uncertain, or completely unknown. The problem appears as a consequence of the fact that many of surrounding urban installations are situated under the surface of the ground and cannot be visually determined or verified. On the basis of on site measurements, the developed method enables compensation of all deficiencies of the relevant data about metal installations involved with the fluctuating magnet field appearing along and around of a power line during an unbalanced fault. The presented analytical procedure is based on the fact that certain measurable quantities cumulatively involve the inductive effects of all, known and unknown surrounding metal installations. The performed quantitative analysis points on at the significance of taking into account the existence of surrounding metal installations.