Page 206 - Electrical Installation in Hazardous Area

170 Electrical installations in hazardous areas

Type of protection ‘n’ (historically in the UK, type of protection IN’)
This type of protection includes industrial equipment which does not get
hot or spark, which was historically selected by users, and adds simplified
forms of protection for sparking equipment or that which gets hot, based
upon the Zone 1 types of protection. By producing detailed requirements,
it removes the doubt which used to exist when only selection by somewhat
general criteria was the order of the day, which led to excessive use of
Zone 1 equipment in Zone 2, needlessly increasing operational expense.

7.4 Protection of electrical apparatus for dust risks

Unlike the situation in respect of gases, vapours and mists, the problems
in relation to dusts are the settling properties which dusts have, and their
conductivity. If dust enters an equipment enclosure in significant quan-
tities, it will settle on the electrical components and by insulating them
could cause excessive heating and, if it is conductive, partial short circuits
and similar faults. The objective with dusts, therefore, is always to prevent
significant amounts penetrating the enclosure. This leads to a very much
simpler situation than that which exists with gases, vapours and mists, as
there is effectively only one form of protection, which is to ensure the dust
remains on the outside of the enclosure.
While some equipment constructed for gas/vapour/mist risks is also
suitable for dusts, this does not necessarily follow, and it should not be
assumed that because equipment is suitable for the one type of medium
it is automatically suitable for the other. It is very important to remember
this as dust risks and gas/vapour/mist risks often coincide and, in such
cases, the electrical equipment must be protected for use in both types of
risk, and the elements of this protection may be separate in each case.

7.5 Apparatus construction Standards

The harmonization of Standards is of paramount importance for members
of the EU as these Standards will be acceptable throughout the EU and,
by an agreement between the EU and the European Free Trade Associa-
tion (EFTA), in EFTA countries also. To this end, those Standards which are
harmonized may be called up in EU Directives as Standards with which
compliance demonstrates fulfilment of the Directive, provided this is veri-
fied by a recognized (notified) certification body. Therefore, the Standards
for equipment protection for gas, vapour and mist risks (with the exception
of those methods restricted to Zone2 use only) have been historically
referred to in 76/117/EEC2 and compliance with them allows the use of
the Distinctive Community Mark (see Chapter 1). With the introduction
of the newer Directive 94/9/EC5, the EEC policy was changed to include
essential technical requirements within the Directive. These are included