Page 31 - Electrical Safety of Low Voltage Systems

14 Chapter Tw o

metal objects, which falling through openings may bridge the gap be-
tween persons and live parts, the degree of protection IPXXD or IP4X
is necessary. These two designations maintain the same previously ex-
emplified logic, with the only difference being the use of the test wire
(length 100 mm and diameter 1 mm) instead of the jointed finger.
It must be clear that the judgment of the electrical engineer is
necessary to establish the optimum degree of insulation of equipment,
in light of both the actual environmental conditions of the location
and its normal operations. It is also important to note that a too severe
degree of insulation, if unnecessary, can damage the equipment by
limiting its ventilation and, thereby, raising its internal temperature
beyond safe limits.

2.2.2.1 Enclosures and Mechanical Impacts
A serious hazard for persons is the accidental rupture of enclosures
due to external mechanical impacts, which can expose live parts and
trigger explosive atmospheres. Enclosures, therefore, must have the
capability to protect their own contents. Such ability is specified by
4
the international IK code, which indicates the degree of protection
against harmful impacts. The IK code rates enclosures through the
code letters IK followed by the characteristic group numeral (00 to
10), indicating an impact energy value in joules (see Table 2.1).
The IK code contemplates the maximum value of impact energy of
20 J; when higher impact energy is required, the IK code recommends
a value of 50 J.

2.2.3 Protection by Obstacles
Obstacles are elements placed between exposed live parts and per-
sons (e.g., fence, handrail, mesh, screen, etc.). They prevent direct con-
tacts by increasing the distance from energized parts, which, other-
wise, would be accessible. Safety is, therefore, assured by keeping
exposed live parts out of reach. Unlike enclosures and barriers,
obstacles could be intentionally circumvented, as, by definition, they
may not be firmly held in their positions; therefore, obstacles offer only
a limited degree of protection and that too only for accidental touch.
This protective measure, consequently, should be exclusively adopted
in areas accessible to skilled personnel in the field of electricity.

IK01 IK02 IK03 IK04 IK05 IK06 IK07 IK08 IK09 IK10
Impact
energy
(J) 0.15 0.2 0.35 0.5 0.7 1 2 5 10 20
TABLE 2.1 Relation Between IK Code and Impact Energy