Selection and Erection of Equipment

The 15th edition Regulations had a restriction on the use of flexible cables for fixed wiring, but this was dropped in the 16th edition, probably because of the increased usage of flexible cables and cords for this purpose. 

Protection is also required against wet and/or corrosive conditions, dirt and pollutants. Regulation 522-05-02 warns against electrolytic action of dissimilar metals in contact where dampness accelerates the corrosion process, and Regulation 522-05-03 refers to hazardous degradation. An 

It is not always appreciated that some cable sheathing materials are adversely affected by the ultraviolet radiation in sunlight, and to counter this effect a black compound is added see Regulation 522-11-01. Unfortunately, this increases the absorption of infrared radiation and this solar heating can increase the cable temperature considerably, so outdoor cables should either be screened from sunlight or derated to allow for an increase in ambient temperature of about 20°C. 

A designer will select a cable type to suit the environmental conditions. The load current and type and rating of the protective device should then be determined, then the current rating of the protective device is divided by the applicable correction factors. The factors are for grouping (Table 4B1, 4B2 

Finally (and if thought necessary), the cable size should be checked to ensure its insulation will not be damaged on the occurrence of a short circuit fault by applying the formula given in Regulation 434-03-03, as discussed in Short circuit protection . 

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Section 2 - Selection and Erection of Equipment deals with picking equipment suitable for its intended use having regard to site conditions, EMC requirements and HV transients particularly where there is IT apparatus. The equipment should be to a harmonised standard if any, or to a BS or other standard. On page 21 of the guidance note there is a specimen circuit diagram showing the information which has to be provided to the user on completion of the installation. 

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