This paper investigates the effect of harmonics due to renewable generation, energy-saving home appliances and electric vehicle chargers. Harmonics were found to be contained at the transmission level due to the presence of shunt capacitors. These shunt capacitors behave like single-tuned or high-pass harmonic filters, however there will be an increased risk of harmonic resonance making the transmission line susceptible to tripping wind turbines on transient overvoltage.Harmonics generated by solar, energy-saving home appliances and electric vehicle chargers pose a potential threat to the distribution network systems and if allowed to continue unabated could cause fuse failures and premature failure of pole-mount transformers. In addition, neutral current can be excessive due to current harmonic distortion even with loads balanced on three phases which will cause overheating if the neutral is undersized.The paper also identifies some areas where further work is required to understand harmonics and their impacts on power system performances.