This test is intended to determine a Device Under Test’s (DUT’s) harmonic current specifications.

It’s commonly connected with transfer mode power converters and other nonlinear loads like generators, transformers, and lamp dimmers/ballasts.

The harmonic demand on local power supplies is minimised by limiting harmonic current pull requirements, which helps to prevent overheating and increases reliability. It’s a critical piece of the puzzle for power utilities to keep the consistency of their AC delivery systems.

Back in the 1890s in London, England, one of the first EMC experiments was performed, with limits stated. Degrading electric lamps can allow arcing between contacts, causing nearby lamps on the same power supply to ‘flicker.’

The impedance of the power supply cabling used to be even higher than it is now. An arcing lamp’s non-linear current pull caused voltage fluctuations on the power supply, impacting neighbouring lamps.

Today’s flicker caps are also based on the level of visually perceptible flickering on an incandescent light bulb.

When a device is first turned on, the voltage difference limit in EN61000-3-3 establishes an inrush current limit. The inrush current when the power is on is determined by turning a client’s product’s power on and off 24 times. The highest and lowest registered values are discarded, and the middle 22 values are summed to obtain the final inrush current value, which is then compared to the maximum.