Page 472 - Handbook of Electrical Engineering
P. 472

MISCELLANEOUS SUBJECTS     461

                 When designing a lighting circuit it is customary practice to size the cables so that the farthest
           lamp from the supply receives no less than 95% of its nominal voltage. In addition it is assumed that
           all the lighting fittings are energised when this design calculation is made.


           18.1.1 Types of Lighting Fittings

           As a general guide to the appropriate types of fittings that can be used, the following are suitable:
           • Industrial weatherproof fluorescent usually double 40 watt tubes for non-hazardous general areas.
           • Ex (e) certified and weatherproof fluorescent, also double 40 watt tubes, for hazardous areas.
           • Ex (e) or Ex (d) certified and weatherproof floodlights of the SON-T type, for areas such as
             well-head, platform legs and sea surface lighting.
           • Ex (e) or Ex (d) certified and weatherproof bulkhead fittings with a single 60 watt incandes-
             cent lamp.
           • Ex (n) certified and weatherproof fluorescent with single or double tubes for Zone 2 and non-
             hazardous areas, and areas where corrosion and determination will be minimal.

                 Note that low-pressure sodium lamps are not generally permitted in hazardous areas because
           they are considered to be a risk with regard to igniting hazardous gases. Fittings made from aluminium
           and its alloys should be avoided because the oxide that invariably forms after a time is considered
           as a potential source of sparks caused by mechanical impact.


           18.1.2 Levels of Illumination

           The levels of illumination needed at different locations and within rooms are given as a general guide
           in Table 18.1.

                                 Table 18.1. Illumination levels of onshore and off-
                                 shore plants
                                 Location and equipment    Illumination level
                                                           in lux, see Note 1
                                 Laboratory                500
                                 Computer room             500
                                 Radio room                500
                                 Gymnasium                 500
                                 Medical treatment room    500
                                 Pharmacy                  500
                                 Helicopter reception offices  500
                                 Helicopter operations office  500
                                 Administration offices     400 to 500
                                 Drawing office             400
                                 Library and reading room  400
                                 Kitchen and galley        300 to 500
                                 Manned process modules    300
                                 Central control room      300 Note 2
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