The cause of damage to the lead sheath of a cable is

crystallisation of the lead through vibration
chemical action on the lead when buried in the earth
mechanical damage
all of the above

The correct answer is D. all of the above.

Lead sheaths are used to protect cables from damage. However, they can be damaged by a number of factors, including:

  • Crystallisation of the lead through vibration: When a cable is vibrated, the lead sheath can become brittle and crack. This can lead to the cable becoming exposed to moisture and other contaminants, which can cause further damage.
  • Chemical action on the lead when buried in the earth: When a cable is buried in the earth, it can be exposed to a number of chemicals, including acids and alkalis. These chemicals can corrode the lead sheath, causing it to weaken and eventually fail.
  • Mechanical damage: Cables can be damaged by a number of mechanical factors, including being crushed, cut, or punctured. This can cause the lead sheath to break, exposing the cable to moisture and other contaminants.

It is important to inspect cables regularly for signs of damage. If you see any damage, it is important to have the cable repaired or replaced as soon as possible.