<p>Provided is a communications system that performs communications while retaining high voltage insulation, therefore enabling communications to be performed by connecting a control circuit operating at a low voltage and a non-control circuit operating at a high voltage via a propagation layer having a waveguide structure. Specifically, a displacement current (surge current) flows between a high voltage circuit and a low voltage circuit, caused by potential difference generated in the high voltage circuit. A surge current protection circuit is provided, preventing input beyond a rating being applied to a communications module and the low voltage circuit by such surge currents.</p>
