The possibility for using the Faraday magneto-optic effect in direct-current (dc) measurement has not been extensively studied so far. However, the demand for dc measurement in industry is rising. It is valuable to investigate the design problems of such devices. This paper presents the design of a low-cost optical-fiber direct current measurement device in a specific application which requires a measurement range from 2 KA to 20 KA for a bus bar in a particular geometry and an accuracy of plus or minus 10% of full measurement scale. An experimental device had a measured performance of nearly plus or minus 6% accuracy of full scale and a dynamic range of 2 KA to 20 KA. The dynamic range can be increased while retaining an error current of approximately plus or minus 1.2 KA.