Page 43 - Electrical Safety of Low Voltage Systems

26 Chapter Tw o

FAQs

Q. Regarding the IP degree of protection that enclosures must provide, what
does it mean that we should consider actual environmental conditions during
the normal operations of equipment?
A. In the decision-making process to establish the optimum IP degree of
protection, we must not consider improbable events that possibly might occur
to the equipment. For instance, an outlet in the backyard of a dwelling unit is
legitimately expected to be subject not only to rain but also to water splashes
from any direction; therefore, the right rating of its enclosure is IPX4 and not
IPX3. On the other hand, an outlet in the living room of the same dwelling unit
will not be subject to rain, or splashes, during its usual and normal operations.
We must not consider, therefore, the presence, for example, of possible floods
in the house, and accordingly overrate the receptacle.
Q. What is the difference between functional and basic insulations?
A. The functional insulation allows the functioning of the equipment by insu-
latingpartsatdifferentpotentials,whereasthebasicinsulationprotectsagainst
direct and indirect contact. The two insulations, therefore, are accordingly
tested with different methods, as they must satisfy different requirements.
Q. What is the difference between direct and indirect contact?
A. Indirect contact occurs through metal enclosures, which are energized due
to the failure of the basic insulation of live parts inside it. Direct contact occurs
by “directly” touching live parts, which were erroneously deemed harmless,
for example, during maintenance of equipment.
Q. Is protection against direct contact by obstacles really safe?
A. Protection against direct contact of open-type equipment by obstacles is
actually realized by two “layers” of protection: The first one is the distance
from live parts, as “marked” by obstacles, which prevent accidental contacts,
and the second one is the technical competence of qualified persons interact-
ing with the open-type equipment.
In essence, obstacles, combined with technical skills, provide a degree
of protection against direct contact, but they are not supposed to prevent
intentional contact with energized parts. Under the above conditions, protec-
tion against direct contact by obstacles can be considered safe.

Endnotes
1. See, for reference, IEC 60364-4-41: 2005, “Low-Voltage Electrical Installations,
Part 4-41: Protection for Safety—Protection Against Electric Shock,” 5th ed.
2. IEC 60529: 2001, “Degrees of Protection Provided by Enclosures (IP Code).”
3. The test is carried out with the aid of a push-type dynamometer.
4. IEC 62262, “Degrees of Protection Provided by Enclosures for Electrical Equipment
Against External Mechanical Impacts (IK code),” 2002-02-12.