This paper reviews established methods of communication using in-building power conductors with particular attention to the 100 kHz to 450 kHz frequency range. It also reviews line characteristic impedance and it presents new measurements of attenuation and noise on the power conductors. Measurements illustrate interfering noise caused by individual electrical loads and also the combined noise at power outlets in an office environment. Using a simple FSK transmission system, bit errors were measured as a function of time and these were found to coincide with noise bursts that occur at regular times during the 60 Hz cycle. The paper concludes by proposing an interference avoidance scheme where transmission is suspended during periods of high interference and then continues during quiet intervals.