Page 59 - Electrical Safety of Low Voltage Systems

42 Chapter Three

Basic Class 0 Class I Tot Class II Class IIBE Electrical
insulation separation
Safety Risk

FIGURE 3.11 A qualitative comparison between safety and risk of protective
measures.

3.10 A Qualitative Comparison Between Safety and
Risk of Protective Measures
Figure 3.11 shows a qualitative comparison of the various PMs exam-
ined in this chapter.
As said in Sec. 3.6, we cannot establish if the risk r BI (t)ofthe
protective measure basic insulation is greater, equal to, or less than
the risk r ITOT (t) of the protective measure Class I. This is due to the
increase in the probability that persons are subject to touch potentials
caused by the metal enclosure. Because of this indetermination, r BI (t)
and r ITOT (t) are shown of equal size in Fig. 3.11.
It should be noted that the above-calculated parameters are valid
only if the manufacturer’s instructions are followed during installa-
tion, the electrical equipment is maintained in relation to the environ-
ment, and we are in standard situations. Equipment in nonordinary
locations (e.g., restrictive spaces, fire hazardous facility, etc.) may in
fact offer greater risks.