This paper presents another way to assess power quality delivered by transformers. The electro-magnetic signal entropy reveals the presence of harmonics in the industrial and domestic electric power supply. It will show some electromagnetic radiated wave measurements taken below 115 kV electric transformers circuits of Manizales city (Colombia) through a non-invasive and indirect measurement (using wireless sensors) of the power complexity transported by the supply. The electric users are concerned over the electric power quality, since poor quality causes many damages and malfunction for different kind of loads. Some industries are very sensitive and many losses occur by instabilities, harmonic distortion, shorts, line disturbances, impulses, notches, glitches, interruptions, over voltages, under voltages, wave faults, computer lockups, flicker, equipment damage (at partial load),data processing equipment PFC instability, overloading problems when switching heavy loads, overheated neutral, problems with long lines, nuisance tripping, utility metering claims, and others.