Abstract: A zero-phase current transformer for use as a leakage current detecting element in a leakage current interrupter in which two magnetic materials of different permeabilities are provided so as to eliminate a range where the leakage current interrupter is inoperable without lowering its ability to distinguish noise components. The different magnetic materials may be provided as a single core constructed by mixing the materials of different permeabilities. Otherwise, the materials can be provided as annually-shaped magnetic pieces stacked one on top of the other. Still further, the materials of different magnetic permeability may be provided as bands of materials interwound to form alternating layers or one of the materials may be provided as at least a portion of a protective case.