Page 250 - Electrical Installation in Hazardous Area

21 4 Electrical installations in hazardous areas

Table 9.1 Separation between live parts through
encapsulant

Minimum distances between bare live parts of
the same circuit, different circuits and any
circuit and earthed metallic parts

Maximum voltage between Minimum permissible
live parts at maximum separation*
rated supply voltage
taking account of faults
and recognized overloads'
(Volts rms) (-1
~
380 1 .o
500 1.5
660 2.0
1000 2.5
1500 4.0
3000 7.0
6000 12.0
10 000 20.0

(From BS 5501, Part S3)

Notes:
1 The voltage in practice may exceed the values above by up
to 10% without the necessity to move to the next highest
figure.
2 Where the separation is between two live parts via an
interposing isolated conducting part the separation required
will be formed by the total of the separations of the two live
parts and the interposing part.

limits applied to the apparatus, but provided this does not damage the
encapsulant or cause the external encapsulant temperature to exceed the
temperature classification, such a situation is acceptable.

Cells or batteries

Only primary and secondary cells, batteries or accumulators which do
not release gas or electrolyte in the normal operating conditions speci-
fied by the manufacturer of the cell or battery may be encapsulated. It is,
however, recognized that in abnormal circumstances such cells or batteries
may release gas (but not electrolyte) and there must be a method of release
of the gas which does not defeat the protection concept. This often takes the
form of a plug of porous encapsulant or a capillary from the top of the cell
or battery to the outside of the encapsulant. It is also necessary to consider
any dimension variation due to such things as charging and this is usually