An electrical device that is arranged to be supplied with power from a power supply and to perform communication via a communication line between a first board and a second board that are separated, the electrical device comprising: - the communication line; - the first board housed in a housing (21, 22) including a metal part; - a power conversion circuit includes a switching element; - a first communication module; - a first signal isolation circuit that allows a communication signal to pass while isolating the first communication module from the communication line; - a first isolated conversion circuit that supplies DC power isolated from power supplied to the power conversion circuit, to the first communication module; - the second board housed in the housing (21, 22) or another housing; - a second communication module performs communication with the first communication module; - a second signal isolation circuit that allows the communication signal to pass while isolating the second communication module from the communication line; - a second isolated conversion circuit that supplies DC power isolated from power supplied to the power conversion circuit, to the second communication module; and - a capacitor that is connected between a conductor to which DC power output to the first communication module from the first isolated conversion circuit is supplied and the metal part of the housing (21, 22), the conductor being a conductor on a negative potential side serving as a voltage reference or a conductor on a positive potential side which is at a higher potential than the negative potential side; - wherein the power conversion circuit, the first communication module, the first signal isolation circuit, the first isolated conversion circuit are mounted on the first board; and wherein the second communication module, the second signal isolation circuit, second isolated conversion circuit are mounted on the second board. the electrical device comprising: - the communication line; - the first board housed in a housing (21, 22) including a metal part; - a power conversion circuit includes a switching element; - a first communication module; - a first signal isolation circuit that allows a communication signal to pass while isolating the first communication module from the communication line; - a first isolated conversion circuit that supplies DC power isolated from power supplied to the power conversion circuit, to the first communication module; - the second board housed in the housing (21, 22) or another housing; - a second communication module performs communication with the first communication module; - a second signal isolation circuit that allows the communication signal to pass while isolating the second communication module from the communication line; - a second isolated conversion circuit that supplies DC power isolated from power supplied to the power conversion circuit, to the second communication module; and - a capacitor that is connected between a conductor to which DC power output to the first communication module from the first isolated conversion circuit is supplied and the metal part of the housing (21, 22), the conductor being a conductor on a negative potential side serving as a voltage reference or a conductor on a positive potential side which is at a higher potential than the negative potential side; - wherein the power conversion circuit, the first communication module, the first signal isolation circuit, the first isolated conversion circuit are mounted on the first board; and - the communication line; - the first board housed in a housing (21, 22) including a metal part; - a power conversion circuit includes a switching element; - a first communication module; - a first signal isolation circuit that allows a communication signal to pass while isolating the first communication module from the communication line; - a first isolated conversion circuit that supplies DC power isolated from power supplied to the power conversion circuit, to the first communication module; - the second board housed in the housing (21, 22) or another housing; - a second communication module performs communication with the first communication module; - a second signal isolation circuit that allows the communication signal to pass while isolating the second communication module from the communication line; - a second isolated conversion circuit that supplies DC power isolated from power supplied to the power conversion circuit, to the second communication module; and - a capacitor that is connected between a conductor to which DC power output to the first communication module from the first isolated conversion circuit is supplied and the metal part of the housing (21, 22), the conductor being a conductor on a negative potential side serving as a voltage reference or a conductor on a positive potential side which is at a higher potential than the negative potential side; - wherein the power conversion circuit, the first communication module, the first signal isolation circuit, the first isolated conversion circuit are mounted on the first board; and wherein the second communication module, the second signal isolation circuit, second isolated conversion circuit are mounted on the second board.