Phasor measurement units (PMUs) are widely used in power transmission systems to provide synchronized measurements for the purpose of fault detection. However, how to efficiently deploy those devices across a power grid – so that a comprehensive coverage can be provided at a relatively low cost – remains a challenge. In this paper, we present a sensitivity study of a PMU-based fault detection method using three different distance metrics. This study can serve as a guideline for efficient PMU deployment. To illustrate the effectiveness of this approach, we have derived an alternative PMU placement plan for a power grid. Experimental results show that our PMU placement reduces the required PMU deployment by more than 80% as compared to the original placement, yet still provides similar level of accuracy in fault detection.