Page 238 - Electrical Installation in Hazardous Area

202 Electrical installations in hazardous areas

A

B
-

Detail of rear inner
corner of compression
element
A = Gland body
B = Sealing ring
C = Cable seal compression element
D = Cable outer sheath
r = 0.25 x maximum cable diameter or 3mm whichever is smaller

Fig. 8.7 Entry protection for flexible (non-armoured) cables

Rotating machines

Rotating machines often have external fans for cooling purposes. While
these fans do not form part of the basic protection of the machine, not
permitting access to the interior of the machine enclosure, they do form
rotating parts and can generate friction heating or sparking due to the fan
catching on its guard. For this reason BS/EN 50014 (1993)' contains require-
ments for such fans and hoods to prevent them from becoming sources of
ignition, or to prevent the loading of the machine beyond its design rating
and the ratings considered in its protection concept. These requirements
include limitations on materials used, mounting restrictions, and enclosure
requirements, most of which are drawn from the basic requirements of
the Standard (e.g., limitations on plastics and on magnesium content of
light metals).
The ventilation openings of fans are required to be IP20 on the air inlet
side, and IPlO on the outlet side, the latter reduction only being permitted
when the geometry of the outlet is such that foreign bodies above 12.5mm
in size cannot access the moving parts, either by falling into them (e.g., if
the outlet is vertical) or by vibration causing their access to be possible. The
IP rating in this case is produced by compliance with a special Standard,
BS 4999, part 105 (1988)19. In addition, running clearances are required to
be a minimum of 1/100 of the maximum fan diameter with a maximum
figure of 5mm. This maximum figure may be reduced to 1 mm for fans of
high machining accuracy and long-term stability.