In Figure 5.1b, we see the single-phase equivalent circuit. Note that
the voltage labeled Vpcc (for voltage at the point of common coupling or
PCC) has harmonic components due to the harmonic current Ih drawn
by the load running through the line impedance. If this voltage at the
PCC feeds additional equipment other than the harmonic generating circuit,
the resulting voltage distortion can disrupt operation of the equipment
if the harmonic distortion is too high. Harmonic limits are
discussed in great detail in IEEE Std. 519