To deal with the problem of high current measurement in electrolytic aluminum industry, a portable fiber-optic current transformer (P-FOCT) is proposed on the basis of the traditional optical fiber current transformer (FOCT). Due to that the galvanometer accuracy is affected by the Faraday phase shift errors which are caused by the flexible sensing coil non-closed optical path and conductor eccentric position in the process of P-FOCT design and installation, the influence of sensing coil errors and conductor eccentric positions on P-FOCT are theoretically analyzed and experimentally tested. The results show that the Faraday phase shift relative error increases with the non-closed angle of sensing coil and decreases with the increase of the distance between conductor and the center of the non-closed length. Moreover, the Faraday phase shift relative error can be decreased by increasing the number of sensor head turns, and its accuracy can be improved.