Page 26 - Electrical Safety of Low Voltage Systems

CHAPTER2

Fundamentals of

Electrical Safety

Mysterious affair, electricity.
samuel beckett (1906–1989)

2.1 Introduction
Electrical safety is not exclusively defined by the prudent conduct of
individuals in the presence of energized objects. A sensible attitude
toward electrical equipment may only prevent direct contact, that is,
an accidental contact with parts normally live (e.g., energized conduc-
tors, terminals, bus bars inside of equipment, etc.).
Persons are also exposed to the risk of indirect contact, that is, con-
tact with faulty exposed-conductive-parts (ECPs). ECPs are items sup-
plied by the electrical systems that are not normally live, but that are
accidentally energized due to failure of the basic insulation (Fig. 2.1).
Indirect contact is more insidious than direct contact, as it may oc-
cur even during the reasonable use of electrical equipment. Safety is
carried out by systematically applying measures of protection against
both types of contacts, which might occur during the common interac-
tion between a person and an electrical equipment. Protection against
direct contact, also referred to as basic protection, is achieved with effec-
tive separation of persons from live parts, whereas protection against
indirect contact, also referred to as fault protection, is accomplished by
automatically disconnecting the supply. In some specific situations,
discussed later in this chapter, fault protection can also be carried out
without disconnection of supply. 1
It is important to note that all electrical systems must be properly
maintained, so as to reasonably prevent danger of electric contacts.

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