The most common cause of cable failure across both electrical power and data/telecom cables is water or moisture ingress.
Here's why it's so prevalent and damaging:
Ubiquity of Water: Cables are installed everywhere – underground, underwater, in conduit, outdoors, in damp basements, and even within buildings where condensation or leaks can occur. It's extremely difficult to completely exclude moisture over decades of service life.
Multiple Failure Mechanisms: Water doesn't cause failure in just one way; it triggers several destructive processes:
Corrosion: Water corrodes metallic conductors (copper, aluminum) and shields/armor, increasing resistance, creating hot spots, and eventually breaking the conductor. Electrolytic corrosion between dissimilar metals is accelerated.
Insulation Breakdown: Most cable insulation (like XLPE, PVC, paper) degrades when exposed to water. Water "trees" (dendritic micro-channels) can form in polymeric insulation, leading to electrical tracking and eventual short circuits. Paper insulation loses dielectric strength.
Swelling & Delamination: Some insulation materials absorb water, swell, and lose their mechanical and insulating properties. Water can also cause layers within the cable (insulation, semicon shields) to delaminate.
Freeze/Thaw Cycles: Water trapped in cracks or conduit can freeze, expand, and cause mechanical damage to the cable.
Conduction Paths: Water provides conductive paths along the cable surface or between conductors, leading to leakage currents, tracking, and shorts.
Often Linked to Other Causes: Water ingress frequently happens because of another initial problem:
Mechanical Damage: A nick, cut, crush, or abrasion during installation or service breaches the outer sheath, allowing water in. (Mechanical damage itself is a very close second most common cause).
Poor Installation: Incorrect pulling techniques, excessive bending, inadequate sealing at terminations or joints, damaged conduit, or improper backfilling in trenches can create entry points.
Degradation of Jacket/Sheath: Over time, UV exposure, chemicals, or thermal cycling can degrade the cable's outer protective layer (jacket/sheath), making it brittle and permeable to moisture.
Other Highly Common Causes (often interacting with water):
Mechanical Damage: As mentioned above. Includes digging damage ("dig-ins"), crushing, abrasion, excessive bending, vibration fatigue, animal chewing (rodents), and damage during installation.
Thermal Degradation/Overloading: Operating the cable above its rated temperature (due to sustained overload, poor ventilation, high ambient temps, or solar heating) accelerates insulation aging, making it brittle and prone to cracking (which then lets water in).
Electrical Stress: Overvoltages (lightning strikes, switching surges) can puncture insulation directly.
Chemical Exposure: Oils, solvents, acids, alkalis, ozone, or corrosive soils can attack insulation or sheathing materials.
Poor Workmanship (Terminations & Joints): The vast majority of cable failures occur at splices or terminations due to improper installation, contamination, inadequate sealing (leading to moisture ingress), or insulation stress points.
Why Water Reigns Supreme:
While mechanical damage might be the initial event, water ingress is the most common process that ultimately leads to the electrical failure of the cable over time. It's a slow, pervasive, and complex degradation mechanism that affects cables in almost any environment and interacts negatively with nearly all other failure causes.
Prevention Focus: Cable design (robust moisture barriers like lead, aluminum laminate, or special polymers), meticulous installation practices (avoiding sheath damage, proper sealing), and good maintenance (inspecting terminations, addressing conduit flooding) are critical defenses against this most common cause of failure.
