Special Requirements Ex ‘i’

EMMUA 214 States: Page 39

i) Cables: Minimum Conductor Size

The diameter of individual wire strands should be not iess than 0.1 mm.

ii) Cables: Outer Insulation Colour

The colour of outer protective insulating covering is, if colour is used as part of the identification, light blue.

iii) Cables: Separation from Non-Intrinsically Safe Cables

Proper cable routing, layout and earthing guard against the intrusion, transference or invasion of parasitic voltages from non- intrinsically safe circuits into the intrinsically safe circuits

Cables in both hazardous and non-hazardous areas should be installed so as to ensure that intrinsically safe circuit cables cannot be inadvertently connected to circuit cables which are not intrinsically safe. This may be achieved by:

separating the different types of circuit cables; or

placing the cables so as to protect against the risk of mechanical damage; or

using cables which are armoured, metal sheathed or screened for specific types of circuits (e.g. all circuits which are not intrinsically safe are run jn armoured cable or all intrinsically safe circuits are armoured).

The armour should be earthed. Screens on intrinsically safe cables should be earthed as shown on the hook up diagram.

A visible spacing of intrinsically safe cables from high current power cables is an adjunct to minimising the effect of parasitic interference and also aids inspection and maintenance

Multicore Cables

Multi-core cables are commonly used in connection with intrinsically safe circuits. However, a number of important rules apply: non-intrinsically safe circuit cores are not to be run in the same multicore as intrinsically safe circuit cores; the cores for each intrinsically safe circuit should be adjacent to each other throughout the cable length; if groups of cores are individually screened, all the cores of any intrinsically safe circuit should (preferably) be run in the same group. If this is not possible, refer to the appropriate superior technical authority for further consideration on specific requirements.

Terminal boxes

Where the terminal box contains more than one intrinsically safe circuit, the enclosure shall meet the requirements of IEC 60079-0. This effectively means that, under these circumstances, the enclosure shall be certified.