The recommendations of this technical report are applicable to electrical and electronic equipment with a rated input current exceeding 16 A per phase and intended to be connected to public low-voltage ac distribution systems of the following types:
These recommendations specify the information required to enable a supply authority to assess equipment regarding harmonic disturbance and to decide whether or not the equipment is acceptable for connection with regard to the harmonic distortion aspect. This document is not to be regarded as an International Standard.
The European standards, IEC 61000-3-2 & 61000-3-4, placing current harmonic limits on equipment, are designed to protect the small consumer's equipment. The former is restricted to 16 A; the latter extends the range above 16 A. Two particular classes of equipment covered are:
Class D Equipment having current with a "special waveshape"
Table III gives the limits for lighting equipment. Class D is defined by a special waveshape (Fig. 1). If the current waveshape of a nonlinear load is within the limits of Fig. 1 for 95% of a half-cycle, then it is deemed to be Class D equipment and must satisfy the limits of Table IV.
Class D equipment is more representative of many of the single-phase nonlinear loads that were previously discussed. Referring to Table IV, the current limit for a given harmonic is based on the input power (mA/W) as well as a maximum current value. Table V shows the latest proposal for limits.
It is not clear from the tables in IEC 61000-3-2 and 61000-3-4 how restrictive the limits are as a function of equipment rating. The table below shows what the resulting current THD limit is for a 220 V device designed to meet the latest IEC proposals.