A device including a power input supplying external AC power to the device via a power cord, a filter filtering noise from outside of the supplied external AC power and thereby generating a filtered AC power, at least one power socket supplying the filtered AC power to at least one other device, and a PLC modem configured to be connected to the at least one power socket and to transmit data to or receive data from the at least one other device via power line communication using the filtered AC power. The device may be used in power line communication systems. A power line communication method uses the device for isolating a power line communication network from a mains grid.