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PLC Studies in China as a Contribution to the Development of International Standards The sources of disturbance are both radiated and conducted: - the emission of electromagnetic noise which can interfere with radio communications for safety or military use, or disturb the radio amateurs; - conducted differential and common mode currents can penetrate in any equipment connected to the network in which PLC is working. The disturbances have two types of origins: - the signal source asymmetry, due to the coupler asymmetry; - the unbalance of the Low Voltage Distribution Network (LVDN) and as a result an common mode to differential mode conversion. The conversion from differential to common mode due to the network unbalance has been analysed in various paper, as for instance in [1]. Different mitigation solutions have been also been proposed in the literature [2, 3, 4], but the research work must be further continued. 3. Standardization at international level Concerning EMC problems, at an international level, two types of standards must be developed: - a product standard; - a network standard. 3.1 The product standard The product standard should be an amendment of the CISPR22 standard and is the task of the Subcommittee CISPR/I/. A first idea was to extend the concept of Longitudinal Conversion Loss (LCL) specific for symmetric telecommunication pairs of wire to the non symmetric power network. Measurements performed in various power networks, as those shown in Fig. 1, have given a large spread of LCL values [5]. It was not possible to arrive to a consensus for the concept based on the LCL value, to be used for the calculation of a voltage limit at the ports of the equipment connected to the network, although that this concept has been well-established for the case of telecommunication lines. After about 4 years of work and a whole series of documents at CD (Committee Draft) stage, the concept did not find the requested qualified majority for approval by the CISPR/I/