In this article, unless otherwise specified, voltages are given as line-to-line voltages; this follows normal industry practice, but it is sometimes a source of confusion. These voltage levels are generally categorized into primary (medium) and secondary (low) voltage levels. Common primary distribution voltages include 11kV, 22kV, and 33kV, which are used to carry power from substations to local transformers. Below is a breakdown of key IEC standards that electrical engineers must know: Among these, IEC 61439 is the most critical standard for any low-voltage distribution board.
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