Abstract: A communication terminal device has circuitry configured to: judge, based on received information, whether or not source of the received information is intra-group communication destination; monitor whether or not the intra-group communication destination is the master unit based on the judgement; acquire the judging criterion information of the intra-group communication destination detected as the master unit; and switch, while the self device is operating by a master unit operation mode and when the other master unit is detected by monitoring, a master unit operation mode of the self device to a slave unit operation mode based on the judging criterion information of the self device and the judging criterion information of the other master unit.

Abstract: A first communication device is connected in a conductive state to a first power line extending from a secondary side of a transformer in a high-voltage power receiving apparatus to a primary side of breakers in a plurality of distribution boards that receive power supply from the transformer. A plurality of second communication devices are respectively connected to a plurality of second power lines respectively extending from a secondary side of the breakers in the plurality of distribution boards. Each second communication device performs power line communication using the second power line connected thereto as a transmission path. Upon receipt of a communication signal, each of the first communication device and the plurality of second communication devices generates a new communication signal including information included in the communication signal and sends the new communication signal through power line communication.

Abstract: A first communication device is connected in a conductive state to a first power line extending from a secondary side of a transformer in a high-voltage power receiving apparatus to a primary side of breakers in a plurality of distribution boards that receive power supply from the transformer. A plurality of second communication devices are respectively connected to a plurality of second power lines respectively extending from a secondary side of the breakers in the plurality of distribution boards. Each second communication device performs power line communication using the second power line connected thereto as a transmission path. Upon receipt of a communication signal, each of the first communication device and the plurality of second communication devices generates a new communication signal including information included in the communication signal and sends the new communication signal through power line communication.