Page 212 - Electrical Installation in Hazardous Area

176 Electrical installations in hazardous areas

7.5.4 Electrical apparatus for dust risks
The British Standard for dusts based upon the International Standard is
not yet published and the current British Standards3 are limited to Zone 21
and 22 (Zone Z and Y). There are currently, therefore, no Standards for the
construction of electrical equipment for Zone 20.
For Zone21 and 22, equipment construction Standards exist. These
mainly cover the degree of enclosure of the equipment, together with
additional construction requirements covering such things as strength, etc.
In one case, the relevant Standard covers the additional requirements
necessary to make equipment constructed for gas/vapour and mist risks
suitable for use in the explosive atmospheres of combustible dusts. The
relevant Standards follow:

BS 6467 (1985) - Electrical apparatus with protection by enclosure for use
in the presence of combustible dusts, Part 1: specification for apparatus
(see Chapter 15)

It will be noted that the Standard particularly draws attention to the fact that
protection is by enclosure. In addition, the Standard differentiates between
equipment suitable for Zone21 and Zone22, and that suitable only for
Zone 22.

BS 7353 (1992) - Guide to the use of electrical apparatus complying
with BS 5501 or BS 6941 in the presence of combustible dust
(see Chapter 15)
This Standard essentially specifies in what circumstances equipment
complying with European Standards (ENS) is suitable for use in explosive
afmospheres of combustible dust and air and what extra constructional
features are necessary. It refers to these European Standards as BS 5501, as
their first editions were given the numbers that follow:

BS 5501, Part 1 (1977) - EN 50014, first edition
BS 5501, Part 2 (1997) - EN 50015, first edition
BS 5501, Part 3 (1977) - EN 50016, first edition
BS 5501, Part 4 (1977) - EN 50017, first edition
BS 5501, Part 5 (1977) - EN 50018, first edition
BS 5501, Part 6 (1977) - EN 50019, first edition
BS 5501, Part 7 (1977) - EN 50020, first edition
BS 5501, Part 8 (1988) - EN 50028, first edition
BS 5501, Part 9 (1982) - EN 50039, first edition

While, as before, these European Standards are now, or soon will be,
replaced by their second editions (which are numbered BS/EN5O and
upwards with the exception of BS 5501, Parts 8 and 9) the differences so
produced are not likely to be sigmiicant and it is likely that in most cases