Page 53 - Electrical Safety of Low Voltage Systems

36 Chapter Three

FIGURE 3.5 Determination of safety as the result of an iterative process.

C 3 in Fig. 3.4) and lower acceptable values for S 0 (i.e., S 1 < S 0 in
Fig. 3.4).
Achieving safety canbe thoughtastheresultofaniterativeprocess
as described in the flow chart of Fig. 3.5.
In following sections, we will examine the standard protective
measures, already introduced in Chap. 2, by analyzing their safety
and risk against indirect contact.

3.5 Safety and Risk of Basic Insulation
Let us calculate safety, and the resulting risk, of an electrical item with
no conductive enclosure, whose live parts have basic insulation (e.g.,
cables in air) (Fig. 3.6).
In the absence of a conductive enclosure, persons can only be ex-
posed to direct contact, should the basic insulation fail. In that case,
electric shock occurs only if the person touches the point of the insu-
lation’s failure, which exposes the live part.