In this paper, we tried to estimate the radiative properties of SF6-C2F4-Cu thermal plasmas existing in High Voltage Circuit Breakers (HVBV). The calculation was realized assuming the Local Thermodynamic Equilibrium (LTE), binary and ternary mixtures with mass concentrations, temperatures from 300K to 30 000K and pressures of 1 bar and 8 bar. Two methods were used to estimate these properties: the Net Emission Coefficient (NEC) by neglecting the lines overlapping and the mixing rules using either the NECs of the pure gases or the NECs of a given SF6-C2F4 mixture and of pure Cu plasma. Some results are proposed and discussed. The tone of the conclusion is that the linear interpolation seems to be a good approximation for low pressure and high temperatures.