In GASEOUS zones :
three types of protection are mainly used for the
design of light fittings for potentially explosive atmospheres:
Increased safety “e”:
The electrical equipment is designed in such a way as
to make it impossible for any source of ignition to
appear inside or outside the unit. Its class of temperature
takes into account the hottest point of the whole unit
(inside and outside), and not only the casing.
Flameproof enclosure “d”:
The electrical equipment is confined in an enclosure
which will stand up to an internal explosion without
permanent deformation and without transmission to the
surrounding atmosphere. Its class of temperature takes
into account the maximum temperature of the outside
surface of the enclosure. A waiting time required for
the cooling of the internal components must be observed
before opening the equipment in the zone.
Zone 2 with restricted breathing
“nA/nR”: The electrical equipment
is designed in such a way as to make it impossible for
any source of ignition to appear outside the unit and
any penetration of the surrounding atmosphere into the
unit. Its class of temperature takes into account the
maximum temperature of the outside surface of the enclosure.
The equipment must be opened away from any potentially
explosive atmosphere.
Other types of protection are recognised (intrinsic
safety “ia” and "ib”,
filling with powder “q”,
encapsulating “m”, etc.).
In combination with the main type of protection “e”,
they are used as a secondary type of protection for
certain components which are likely to produce arcs
or sparks in normal use (ballast, switches, etc.). They
are little used as the main protection of light fittings.
In DUSTY zones :
the type of protection is based on two principles:
Dust proofing:
• IP6x for zones 20 and 21 and
for conducting dusts in zone 22.
• IP5x for non conducting dusts
in zone 22.
The maximum temperature of
the surface:
this must be less than the lower of the two following
values:
• 2/3 of the spontaneous combustion temperature
of the cloud of dust under consideration.
• the spontaneous combustion temperature of a
layer of dust 5 mm thick decreased by 75°C.
|
|
Zones 1 & 2, 21 & 22
