The easiest, low risk way to procure cables is to specify products that have proven their quality in similar projects. However, this may not always be possible as the end use may impose requirements that an established cable cannot meet.

If so, the next-best option is to insist that cables must meet relevant national or international standards, plus independent approval and certification requirements. By doing so, the onus of meeting the specification is placed upon the supplier.

Standards and variations

Standards allow the issue of supply tenders which are manufacturer-neutral. The cable specification and tender can be kept simple by tying together the relevant standard and certification requirement, but nothing else. For example, low smoke halogen free armoured cables for use in the UK may be easily specified by stating: “BS 6724, BASEC approved”.

If a specifier decides instead to write out a detailed specification, they assume the risk of any omissions or modifications made. It is therefore advisable to check existing standards using the same materials, voltage rating and performance characteristics in order to establish, for instance, appropriate insulation thicknesses as safety is paramount in cable design. Also, it is sometimes tempting to over-specify products, including excessive detail that is already included in a related specification such as a standard. By specifying conformity solely to the standard, all the construction, material detail and applicable testing listed in the standard are by default included and need not be repeated.

Items which may need specifying are, where applicable, choice of insulation or sheathing materials (for example EPR or XLPE for medium voltage cable insulation), core colors (where alternatives are needed and allowed) or any other variable options which are often set out in the cable standard, for example fire performance. Although some cable standards include an informative section on ‘what to state on your order’, which can be a useful guide for specification; it is recommended that you familiarize yourself with the cable standards you use so that you can better understand the stipulations, and keep the latest copies for ease of referencing them.

Potential risks can arise when a cable standard does not clearly recognize precise construction and performance characteristics that may be required. This can occur when standards set restrictions on the allowable constructions; for example, some medium and high voltage cable standards do not currently include low smoke halogen free sheath materials as an option, even though these materials have in some sectors become de facto minimum specifications.

Conclusion

Bespoke cable specification can be fraught with pitfalls unless the writer is highly experienced in cable standards and knows exactly what is wanted. If in doubt, always consult with experts to ensure trouble-free procurement.