Page 246 - Electrical Installation in Hazardous Area

21 0 Electrical installations in hazardous areas

3. Definition of enclosure material for non-metallic enclosures (encap-
sulation is not, strictly speaking, a non-metallic enclosure although
non-metallic in substance).
4. Encapsulation is not required to be given a temperature index as,
although it is non-metallic, it is not a plastic as defined in BS 5501,
Part 1 (1977). The encapsulant is, however, required to pass the thermal
endurance tests prescribed by that Standard.
5. The requirements for threaded holes in plastics enclosures do not apply
to encapsulation as there are no parts of the encapsulant which can
readily be dismantled without destruction of the encapsulant.
6. Because no parts are intended for removal the requirements for inter-
locking are excluded, together with those for fasteners.
7. The requirements for cable and conduit entries are excluded as in this
protection concept, the cable is sealed into the encapsulant.
8. The requirements for switchgear and fuses are also excluded as they
mostly address the prevention of access and no access is possible when
encapsulated.
9. The warning label for luminaires is also not necessary as they also
cannot be opened if encapsulated.
10. A group of the tests is excluded as follows:

(a) it is not necessary to impact test Ex 'm' components;
(b) tests for degree of protection of enclosures are irrelevant;
(c) tests in explosive mixtures are irrelevant as the explosive mixture
does not have access to the electrical circuits;
(d) tests for cable clamping are not necessary because the end of the
cable is sealed in the encapsulant.

BS 5501, Part 8 (1988) also contains further definitions which supplement
those in BS 5501, Part 1 (1977)4 and BS/EN 50014 (1993)5. These will be
included in the list of definitions at the end of this book.

9.1.2 Specification of the encapsulation
The compound used for encapsulation must be fully defined including
its exact material with detail of fillers, other additives and any surface
treatment given after encapsulation (e.g., varnishing). Its temperature range
needs to be defined together with its maximum continuous operating
temperature (which may be higher than the upper range limit as the
temperature range is the range through which the material satisfies BS
5501, Part 8 (1988)3). It is helpful if an encapsulating material with an IEC
reference number can be used.
The encapsulant is also tested to confirm its insulating properties and
its resistance to water absorption, the latter test only being specified as