Question: what is 1st 2nd and 3rd harmonics?
Answer: A Fundamental Waveform (or first harmonic) is the sinusoidal waveform that has the supply frequency. ... So given a 50Hz fundamental waveform, this means a 2nd harmonic frequency would be 100Hz (2 x 50Hz), a 3rd harmonic would be 150Hz (3 x 50Hz), a 5th at 250Hz, a 7th at 350Hz and so on.