Brochure/Catalogue

The basics of explosion protection
Equipment group II applies to equipment and devices
intended for use in other places liable to be endangered by
explosive atmospheres.
Equipment group II is subdivided into three categories:
Category 1
These devices may be used in a zone where explosive
atmospheres are continually or often present.
These devices must provide the required safety and
explosion protective mechanisms to ensure, even during
rarely occurring faults, that
• If a protective safety mechanism fails, the required level
of safety is guaranteed by at least one other independent
safety mechanism, or
• The required level of safety is guaranteed even when two
independent faults occur
Category 2
These devices may be used in zones where an explosive
atmosphere (from gases, vapours, mist or air-borne dust) is
not anticipated, but could occur for a short period. These
devices guarantee the required safety level during normal
operations.
Category 3
These devices may be used in zones where an explosive
atmosphere (from gases, vapours, mist or air-borne dust)
is not anticipated, but could rarely occur for a short period.
These devices guarantee the required safety level during
normal operations.
Protection concepts
The selection of the ignition protection type is based on
the zone categories described above. In the ATEX eld of
application for example, the Ex ia ignition protection type is
permitted for Zone 0 (the highest probability of an explosive
atmosphere).
Increased safety Ex e – no sparks and surface
temperature limited to a safe level
This increased safety level is intended for
products that encounter no sparks during
normal operations or during faults. The
surface temperature of the relevant
components is limited to a value below the
ignition temperature. An increased safety level is reached by
reducing the current load, by improving the insulating
properties, and by maintaining clearance and creepage
distances which exceed those used in standard industrial
applications. This protection strategy is typically used in
junction boxes.
Intrinsic safety Ex i – ignition energy limited
to a safe level
Intrinsic safety is intended for products in
which the electrical energy that ows into,
or is stored in, the product is not sufcient to
ignite the surrounding explosive
atmosphere. This must also hold true for
fault scenarios. Because of the way this intrinsic safety is
achieved, it is essential that not only are the devices exposed
to the explosive atmosphere properly constructed, but the
connected electrical devices are also constructed and
designed accordingly. Intrinsically safe devices and
intrinsically safe equipment components are divided into
protection categories „ia“ (for Zone 0, 1 and 2), „ib“ (for Zone
1 and 2), and „ic“ (only for Zone 2). A typical application is
for control and display circuits using low voltage and low
current.
Flameproof Ex d encapsulation
Limits the explosion to the interior of the enclosure
Flameproof enclosures are designed for
devices that generate sparks or have hot
surfaces which are capable of ignition in
normal operations. With this type of ignition
protection, industrial components – which
normally could not be used in explosive atmospheres – may
be used when they are installed within ameproof
enclosures.
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