A method and device for reducing interference between a first signal of the carrier current type (Se) transmitted between modems (MCPL) in an electrical network (Re) and a second signal (S) transmitted between modems (M) in another network (R), the signals (Se, S) being coded by distribution of the data over allocated carrier frequencies in the same reserved frequency band (BF). The method includes: a step of measurement, by each modem (MCPL) in the electrical network, of transmission characteristics of each carrier frequency (F) that may be used for coding the first signal (Se), a step of detection, by analysis of the measured transmission characteristics, of at least one second, carrier frequency (F2,n), which is allocated or may be allocated for coding the second signal (S) and is common with at least one first carrier frequency (F1,m), which is allocated for coding the first signal (Se), and a steps of optimisation of the distribution of the data of the first signal (Se) over carrier frequencies.