thuba SAnR Manuel page 5

ZONE 2
5
The equipping of the explosionproof switchgear
combinations with switching devices, compo-
nents and terminals is restricted to such a
degree that, in spite of internal dissipation loss-
es, the surface temperatures satisfy the require-
ments of the respective temperature class. The
surface temperature of the enclosure may
exceed the ambient temperature by max. 20
Kelvin. This is to prevent the ingress of an explo-
sive atmosphere into the enclosure due to large
differences in temperature (refrigerator effect).
Adherence to the surface temperature (the
hottest spot on the exterior of the enclosure) in
accordance with the respective temperature
class and the difference in temperature in rela-
tion to the ambient temperature is ensured by
the manufacturer by means of a routine test.
In accordance with IEC 60079-17 'Electrical
installations inspection and maintenance',
restricted breathing enclosures shall be tested
periodically for leaks. When carrying out main-
tenance work, it is necessary to ensure that any
built-in equipment (such as control units, cable
bushings and windows) are not damaged and
that the enclosures are sealed tightly at all times.