EN/IEC 61000-3-3

EN/IEC 61000-3-3 limits voltage changes, voltage fluctuations, and flicker that mains-connected equipment up to 16 A per phase can inject into the public low-voltage supply. This article explains its scope, flicker severity indices, and Compatible Electronics' accredited voltage flicker testing. Part of the Compatible Electronics Learning Center.

What is EN/IEC 61000-3-3?

IEC 61000-3-3 (harmonized in Europe as EN 61000-3-3) is Part 3-3 of the IEC 61000 series on electromagnetic compatibility. It limits voltage changes, voltage fluctuations, and flicker that equipment with a rated input current of 16 A or less per phase, and not subject to conditional connection, can cause in the public low-voltage supply network. It is a companion standard to IEC 61000-3-2 (harmonic current limits).

Voltage fluctuations and flicker are caused by loads that draw varying current from the supply — motors starting, welders, arc furnaces, and even switching power supplies cycling between different load states. When these fluctuations are rapid enough and large enough, they cause visible lamp flicker that can be irritating or even harmful to light-sensitive individuals. IEC 61000-3-3 ensures that individual products connected to the public supply do not generate unacceptable levels of flicker. Compatible Electronics provides voltage flicker testing services.

Key Parameters: Pst and Plt

Pst — Short-Term Flicker Severity

Pst is calculated from a 10-minute observation window of voltage fluctuations using a flickermeter defined in IEC 61000-4-15. It reflects human perception of lamp flicker over a short observation period. The limit is Pst ≤ 1.0, meaning the flicker level must not exceed the human visual threshold of annoyance during normal operation.

Plt — Long-Term Flicker Severity

Plt is calculated from a two-hour observation window using a rolling average of Pst values. It characterizes sustained flicker over a longer period. The limit is Plt ≤ 0.65. Plt is particularly relevant for equipment that cycles through different operating states repeatedly over extended periods.

d(t) — Relative Voltage Change

The maximum relative steady-state voltage change d(t) must not exceed 3.3%, and the maximum relative voltage change dc must not exceed 3.3%, with d(max) limited to 4% in most cases. These limits ensure that voltage steps caused by equipment switching do not cause perceptible dimming or brightening of lamps.

Standard Version	Locations Accredited
IEC 61000-3-3 (2013) + AMD2 (2021)	Lake Forest/Silverado
IEC 61000-3-3:2013/AMD2:2021/COR1:2022	Lake Forest/Silverado
EN 61000-3-3:2013/A2:2021/AC:2022-01	Lake Forest/Silverado
EN 61000-3-3 (2013)	Lake Forest/Silverado, Brea, Newbury Park
IEC 61000-3-3 Ed. 2.0 (2008)	Lake Forest/Silverado, Brea, Newbury Park
KS C 9610-3-3:2020	Lake Forest/Silverado, Brea, Newbury Park

EN/IEC 61000-3-3

EN/IEC 61000-3-3

What is EN/IEC 61000-3-3?

Key Parameters: Pst and Plt

Pst — Short-Term Flicker Severity

Plt — Long-Term Flicker Severity

d(t) — Relative Voltage Change

Related Resources

Ready to Test Your Product?

get started?