7
Fig 3 Remote indication in Zone 2 hazardous area
To comply with the requirements of
BS EN 60079:
14 Electrical installations design,
selection and erection
, each of the wires entering
the hazardous area should be individually fused
and contain a means of isolation. These two
requirements are frequently satisfied by using
switch fuse holders with easily removable fuses
which can be extracted to achieve isolation as
shown in Fig 20. This is a satisfactory method at
the low voltages and currents common in
instrumentation systems. Clear identification of,
and easy access to the means of isolation is
essential for their effective use. It is also necessary
to ensure that the maintenance procedure makes
sure that unauthorised re-closure of the switches
does not occur. It is not considered necessary to
have a means of isolation or electrical protection
for the screen.
For some applications Ex nA instrumentation
energised by a current limited power supply or
instrument that can be switched off, is often
considered adequate and to comply with the
requirements of the standard.
