BASEC News

Life Expectancy of Cables

07/04/09
Installers and end users often ask BASEC about the expected lifetime of a cable, particularly when looking at an older installation or when considering refurbishment.

There are no requirements for life expectancy set out in cable standards and specifications.  However, reputable cable manufacturers will state a probable life expectancy for their products, which for building wiring is usually 20 years when run at the rated temperature.  However, under ideal circumstances, with lower loadings and minimal heating, it has been observed that cables can remain safely in operation for up to 50 years.

Cables degrade over time primarily due to changes in the polymers used for insulation and sheathing.  The main cause of polymer degradation is too much heat, from either excessive current loading or from the environment - such as heated spaces.  Cables loaded or heated for 24 hours a day will degrade faster than those used only during working hours – for example, commercial lighting circuits are often operated continuously.

If cables are overheated or overloaded it is possible to estimate reduced lifetimes.  For example, regular PVC installation cables might last for 20 years if used at their rated temperature of 70ºC, but this would reduce to seven years at 80ºC and a matter of months if operated above 100ºC.

The conductors of a cable will normally maintain their performance indefinitely, but if accessories are changed frequently, crushing damage may occur to the exposed ends.  Corrosion can sometimes occur with aluminium conductors and rusting can also affect the conductivity of steel armour.

Cables mounted or used outdoors are prone to very rapid degradation by UV exposure, so it is important that a type recommended for outdoor use is employed.

When deciding whether cable should be replaced during a refurbishment, installers and end users should not just look at the cable as it is now, but consider the possibility of degradation and failure in the period before it is next likely to be assessed, which might be another 10 years.  If a major refurbishment is underway it may be less disruptive to replace cables now, rather than take the risk.

Further information and assistance is available at www.basec.org.uk, technical@basec.org.uk, or contact BASEC directly on 01908 267300

 

 

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