IEC Standards: IEC 61000-3-3: Limits - Limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment with rated current ≤ 16 A per phase and not subject to conditional connection.

IEC 61000-3-3 provides test guidelines for flicker. In the words of the IEC: "This section of IEC 61000-3 is concerned with the limitation of voltage fluctuations and flicker impressed on the public low-voltage system. It specifies limits of voltage changes that may be produced by equipment tested under specified conditions and gives guidance on methods of assessment. This section is applicable to electrical and electronic equipment having an input current up to and including 16 A per phase and intended to be connected to public low-voltage distribution systems of between 220 V and 250 V at a 50-Hz line to neutral."

Although IEC 61000-3-3 is somewhat less controversial than IEC 61000-3-2, the limits are unnecessarily stringent for commercial and industrial environments. IEC 61000-3-11 provides some relief by assessing lower Zref values. Also, many people think that the inrush requirements and test methods are unstable and unjustified.

There are some very interesting—and even confusing—statements in IEC 61000-3-3. For example, Section 5 states, "If voltage changes are caused by manual switching or occur less frequently than once per hour, the observation-period Pst and Plt requirements shall not be applicable. The long-term observation period, Plt, is flicker severity evaluated over a long period (a few hours) using successive short-term observation-period, Pst, values. Pst is flicker severity evaluated over a short term (in minutes). The three requirements related to voltage changes shall be applicable with the previously mentioned voltage values, multiplied by a factor of 1.33."

Further, the specification requires the user to make subjective decisions because of imprecise wording such as that found in Sections 6.1 and 6.5. In any case, this document must be used until a replacement is finished and becomes the standard.