Page 280 - Handbook of Electrical Engineering

HAZARDOUS AREA CLASSIFICATION 265

lint and dust, seepage, external condensation and spraying of water, oil or coolant. These enclosures
must have oil-resistant gaskets and when intended for wall or machine mounting, must have mount-
ing means external to the enclosure cavity. There are no conduit knockouts or unsealed openings
providing access into the enclosure cavity. All conduit openings must have provisions for oil-tight
conduit entry.

10.7 CERTIFICATION OF HAZARDOUS AREA EQUIPMENT

In general the installation designer and the user require confidence that manufactured equipment for
use in a hazardous area carries an internationally recognised certificate. In addition the certificate
should be the result of laboratory testing of a sample of the same equipment. The laboratory should
be specialised in the type of testing required.
In the UK and Europe a certificate is required from the manufacturer for equipment that is to
be used in Zone 1 and Zone 2 areas. In some situations a certificate will be obtained for a system of
components, for example with intrinsically safe equipment.
In the USA the practice is slightly different. Only equipment that will be installed in a Division
1 area should require a certificate.
For manufacturers offering a range of products, the process of testing and obtaining a certificate
is expensive and time consuming. Subsequent modification to a design can also be a long and
expensive process for retesting and re-approval.

Over the last 15 years there has been a process called ‘harmonisation’ of the various national
standards within the UK and Europe with the internationally accepted IEC standards. This has made
the subject of certification rather complicated, but as time passes the results should be simpler to
obtain both for the manufacturer and to the satisfaction of the user.
The harmonisation process has been managed by the Committee of Electrotechnical Stan-
dardisation (CENELEC) in Europe. The committee standardises many subjects of electrical and
electronic engineering, not only those pertaining to hazardous area equipment and its installa-
tion. When equipment is certified in accordance with a CENELEC standard the symbol ‘Ex’ is
modified to become ‘EEx’. This serves to give the designer and the user extra confidence in the
certification.
The certification process, like so many other manufacturing functions, is now being influ-
enced by the generally accepted requirement for quality assurance, through the ISO9000, 9001 and
9002 standards.
There are several permutations for certification involving European harmonisation and coun-
tries inside or outside the EC (European Community). Equipment can be manufactured in any country.
The manufacturer may choose to design his equipment to the national standards of his country, or he
may wish to cover a wider market by using an international or even a CENELEC standard. Once the
equipment is manufactured, samples of it will need to be tested. There may be a testing authority in
the particular country, or for some reason the manufacturer may choose to have the testing carried
out in another country e.g. the testing laboratory may have a wider scope of facilities. Eventually the
manufacturer will obtain a certificate. The installation designer and the user may need to carefully
scrutinise the whole sequence of events leading up to the issuance of a valid certificate. Refer-
ence 1 explains the European situation in detail, together with the various types of certificates that