The IEC 61000-3-3 is an EMC standard by the International Electrotechnical Commission on the limitations of voltage fluctuations and flicker impressed on the public low-voltage system. It specifies conditions, procedures, and limits of voltage changes that may be produced by equipment under test (EUT). This standard applies to electrical and electronic equipment having an input current up to and including 16 A per phase and is intended to be connected to public low-voltage distribution systems of between 220 V and 250 V at 50 Hz line to neutral.

This standard does not apply to the equipment with reference impedance Zref of 6.4. Such equipment can be tested according to IEC 61000-3-11. Part 3-11 applies to equipment with rated input current ≤ 75 A per phase and is subject to conditional connection. Voltage fluctuations are the unwanted changes in the voltage supply from a.c. mains. Voltage flicker is the unsteadiness of a light stimulus whose luminance fluctuates with time. Varying current loads cause voltage fluctuations. If the fluctuations are large enough, they can cause an electric bulb or light to flicker with time. In addition to the unreliable output, the flickering of electric lights has adverse effects on human health. Lighting flicker causes headaches, mental strain, annoyance, migraines, and some people can suffer from epileptic seizures.

Voltage fluctuations can also cause the opening of protection circuits of a device and interrupted loss of power to the other parts of the device. Heavy load equipment like washing machines, TVs, DC generators, motors, etc. causes a fluctuation for a short time in the local voltage due to large inrush currents.  This inrush current can also open fuse in the devices causing an interruption in operations.

The IEC 61000-3-3 specifies the limits on voltage variations that are generated across a reference load of a EUT based on the following factors:

• Relative maximum voltage
• Short-term flicker (Pst)
• Long-term flicker (Plt)

Equipment required for this standard are:

• Harmonics or Flicker analyzer
• AC mains supply
• EUT

Pst is observed over 10 minutes by the flicker analyzer or flicker meter. The part of the waveform that produces the least favorable sequence of voltage change will be considered the short flicker. The short-term flicker cannot exceed the value 1 of the flicker meter. 

Plt is observed over 2 hours and should not exceed 0.65.

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