What is the life expectancy of electrical cables?
Cables don't come with an exact life expectancy, and as the material compounds are refined and developed, so the durability extends further. It's been a common benchmark that a likely life expectancy based on typical conditions could be assumed to be 25 years, but we all have examples of cables far outlasting that timeframe. After all, the copper and aluminium conductors themselves will themselves be operational for far longer.
Take for example household fixed wiring cable with typical electrical loading, wired using the appropriate wiring guidelines. You'd legitimately expect this to last 25 years. When was the last time your house was re-wired? There'll be plenty of examples of cables where they've been found in relatively good condition up to 50 years after installation.
So what does determines the life expectancy? It's the different environmental and operational conditions that influence the longevity of electrical cables in service.
Obviously, the main factor in life expectancy is quality and compliance. It has to be manufactured within tolerances of the standard. Any non-conformance will most likely result in premature failure. Has that quality and compliance been verified? And is it the right cable - does the specification match the performance demands, installation design, and environmental challenges it will face during its lifespan? The more closely it is tailored to the installation, the fewer stresses placed on it that it's can't withstand.
Performance demands: Is it the right size and how is it being used in operation? When a current passes through the cable conductor it generates heat - the higher the current the more heat will be generated. This will have a significant impact if the conductor is undersized or continuously at or near the cable’s maximum permissible (rated) load, degrading the insulation and sheathing materials over time until they become dangerous and require replacement.
Installation design: How are they installed? Although it is primarily the condition of the insulation and sheathing materials rather than the actual conductors that determine the longevity of the cables (given the aluminium and copper conductors will far outlast them), water ingress and poor fixings can also cause corrosion and damage. Joints, connections and terminations are points of weakness which should be monitored. Water ingress could longitudinal along the insulation or through the interstices of a stranded conductor, but it could also be radial if the sheathing and insulation is pierced by external objects (a sharp stone it's laid on over time for instance). Will they be installed in cable ducts liable to flooding? Waterlogged ducts can cause moisture ingress over time through the sheath - again, a reason to consider waterblocking measures. There's numerous things to consider when looking at the installation design to ensure it is unimpeded in operation.
What external factors is the cable exposed to? The insulation and sheathing materials of cables may degrade over time when exposed to temperature extremes, UV light, ozone, various chemicals, excessive flexing or mechanical action, and even potential attack by termites and rodents. Can the specification be tailored to provide resistance to this? For instance, think about 'Desert grade' sheathing and UV resistance if needed. What's the ambient temperature it's operating in - has this been factored into the cable calculations and adjusted accordingly?
Specification is a balance between all these factors. If the cable meets the quality and compliance requirements, then the better the match, the longer it will likely last!
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