In transformlerless PV systems, the leakage current reduction is one of the most important issues. Many interesting single-phase dc-bypass transformerless PV inverters have been proposed for the leakage current reduction. And there is a well known conclusion that the clamping topology is better than the unclamping one in terms of leakage current reduction. However, is this conclusion correct for three-phase dc-bypass ones? The main objective of this project is to investigate the impact of clamping and unclamping dc-bypass switches on the leakage current reduction capability of three-phase transformerless inverters. The findings reveal that the conclusion is different from the single-phase dc-bypass ones. The theoretical analysis and experimental results are provided to verify the new insights.