Page 44 - Electrical Safety of Low Voltage Systems

Fundamentals of Electrical Safety 27

5. The residual current is also referred to as zero-sequence current.
6. Electrical energy is mostly transported and supplied by using a so-called three-
phase AC system. In normal situations, voltages, or currents, have a relative
◦
phase angle of 120 .
7. As per IEC 61008-1: 1996-12, + A1:2002, + A2:2006, “Residual Current Operated
Circuit-Breakers Without Integral Overcurrent Protection for Household and Similar
Uses (RCCBs).”
8. The magnitude of I G depends on the grounding system adopted, as its actual
path back to the source may, or may not, include the earth. This analysis will
be performed in the next chapters.
9. See Chap. 12.
10. The “layers” of protection of Class I equipment are constituted by the basic
insulation and the disconnection of supply, as better explained in Chap. 3.
11. By the term qualified we intend persons responsible, capable, and trained to
perform electrical tasks.
12. IEC 61558-1: 2005-09, “Safety of Power Transformers, Power Supplies, Reactors and
Similar Products—Part 1: General Requirements and Tests.”
13. In case the system does not comply with the above two conditions, the system
becomes an IT system, as explained in Chap. 9.