A closed-circuit power line communication system for a large capacity load, the system comprising: a transmission means connected to one side of a power line in series to generate a communication signal and transmit the communication signal through the power line, and at least one or more reception and load means connected to both sides of the power line in parallel to receive and detect the communication signal transmitted through the power line and control a corresponding load, wherein the transmission means includes at least a switching control unit for generating and transferring a switching control signal to a first switch unit and a second switch unit to generate a power line communication signal, the first switch unit connected to one side of the power line in series to perform a switching operation by the switching control unit, and the second switch unit connected to the first switch unit in parallel to perform a switching operation by the switching control unit; and characterised in that the switch control unit outputs a control signal for short-circuiting the second switch unit during a period when a communication is not performed, disconnecting the second switch unit when a power line communication is performed, and outputting a switching signal for a predetermined communication signal to the first switch unit in synchronization with a power waveform, in which the switching signal includes a switching signal for disconnecting the first switch unit for a predetermined time period (t △before) before arriving and up to a zero cross of the power waveform flowing through the first switch unit, or for a predetermined time period (t △after) after and starting from said zero cross or for a predetermined time period (t △1) that starts before a zero cross of the power waveform flowing through the first switch unit and ends after said zero cross. a transmission means connected to one side of a power line in series to generate a communication signal and transmit the communication signal through the power line, and at least one or more reception and load means connected to both sides of the power line in parallel to receive and detect the communication signal transmitted through the power line and control a corresponding load, wherein the transmission means includes at least a switching control unit for generating and transferring a switching control signal to a first switch unit and a second switch unit to generate a power line communication signal, the first switch unit connected to one side of the power line in series to perform a switching operation by the switching control unit, and the second switch unit connected to the first switch unit in parallel to perform a switching operation by the switching control unit; and characterised in that the switch control unit outputs a control signal for short-circuiting the second switch unit during a period when a communication is not performed, disconnecting the second switch unit when a power line communication is performed, and outputting a switching signal for a predetermined communication signal to the first switch unit in synchronization with a power waveform, in which the switching signal includes a switching signal for disconnecting the first switch unit for a predetermined time period (t △before) before arriving and up to a zero cross of the power waveform flowing through the first switch unit, or for a predetermined time period (t △after) after and starting from said zero cross or for a predetermined time period (t △1) that starts before a zero cross of the power waveform flowing through the first switch unit and ends after said zero cross.