AC electrical loads are referred to either as linear or non-linear depending on how they draw current from the mains power supply waveform.
With a linear load, the relationship between the voltage and current waveforms are sinusoidal and the current at any time is proportional to the voltage (Ohm’s law). Examples of linear loads would include transformers, motors and capacitors.
On the other hand, with a non-linear load the current isn’t proportional to the voltage and it fluctuates based on the alternating load impedance.
Common examples of non-linear loads include rectifiers, variable-speed drives and electronic devices such as computers, printers, TVs, servers and telecoms systems that use switched-mode power supply (SMPS) power conversion technologies. They are also typically found with blade servers.
Non-linear loads draw in currents in abrupt short pulses. These pulses distort the current waveforms, which in turn generates harmonics that can lead to power problems affecting both the distribution system equipment and the loads connected to it.
Harmonics can cause problems such as distortion of the mains supply voltage, equipment overheating, nuisance tripping of circuit breakers, and misfiring of variable speed drives.