An in situ methodology is proposed to characterize the impedance mismatch at each power line communication transmission port in medium voltage network. Based on path loss and impedance measurements, a complete characterization of a non energized medium voltage network is performed. Being able to propose a power budget at each transmission port can be also useful for EMC standards and impedance matching issues. Since power can often be switched off in medium voltage, it is interesting to analyse the behaviour of the network in these conditions