Page 241 - Electrical Installation in Hazardous Area

General requirements for exptosion protected apparatus 205

o - oil immersion (Chapter 9)
p - pressurization (Chapter 11)
q - powder filling (Chapter 9)
d - flameproof enclosure (Chapter 10)
e - increased safety (Chapter 12)
ia - intrinsic safety (Chapter 13)
ib - intrinsic safety (Chapter 13)
m - encapsulation (Chapter 9)

In some cases the apparatus may use two or more types of protection. In
such cases, both protection concept markings will appear with the main
protection concept coming first. (e.g., a luminaire which is type 'e' with an
isolating switch which is type 'd' will be marked 'de'
II: this shows the apparatus is Group I1 for surface industry. (Equip-
ment for coal mining use is Group I.) Where surface industry apparatus
is sub-grouped, typically because it is intrinsically safe or flameproof, and
its performance is different with different gases from the spark ignition or
flame transmission point of view, the symbols will be 'IIA', 'IIB' or 'IIC'.
(If only Group I1 is present the apparatus is suitable for all Group I1 gases,
vapours and mists. In some cases the apparatus may be intended for a
specific gas or vapour only, and in these cases the group or sub-group
marking is not used being replaced by the chemical formula of the gas or
vapour in question (e.g., NH3)
T: T1 to T6 is marked to show the temperature classification of the appa-
ratus. Exceptionally, if the apparatus has a maximum surface temperature
less than a particular class maximum, it may be marked, for example 35 "C
(Tl). If the maximum temperature reached by the equipment is greater than
the T1 class limit (1450 "C), then no class limit is shown and the equipment
is marked only with the actual maximum temperature reached (e.g. 600 "C).
Where the apparatus is marked for use with one particular gas or vapour
only, as above, no temperature classification marking will appear.
Ti: Where an ambient temperature range, other than -20°C to f40"C
is used the symbol 'Ta' or 'Tamb' may appear, together with the actual
ambient temperature range, for example, Ta(-30 "C to +55 "C)
X: The symbol 'X' appears when there are special conditions necessary
for the safe use of the apparatus and these cannot be identified effectively
on the apparatus label. This symbol does not appear with the certification
code marking (e.g., EEx q I1 T4) but as after the certificate number or test
house reference (e.g., BAS 92 3054X)
LI: This identifies the fact that the equipment in question is an Ex compo-
nent and cannot alone be used in an explosive atmosphere. Components
are also not normally marked with a temperature class as this is deter-
mined by its ultimate use. In addition, it is not normal for an 'X' mark
to appear on a component as this is concerned with safe use, and as the
component cannot be used without further certification or testing it is not
appropriate. Typical examples of apparatus marking are given in Fig. 8.8
and 8.9.