Inspect the cable insulation

Check if there is 

• Visible mechanical wear or damage from excessive loadings.
• Visible damage from excessive electrical loadings in the form of discoloration or melted material.

If the damage is only at the end of the cable 

Cut off the damaged section and check that the length remaining is sufficient.

If the cable is too short it must be renewed or a new section of cable added 

• See Replacing a cable .
• See Splicing using insulated moisture proof butt connector . Splicing cable

If there is damage along the cable 

Replace the cable with a new one 

• See Replacing a cable .

For small areas of damage such as scratches (not deep ones) it can be enough to apply reinforcement to the cable insulation by using a heat-shrinkable tubing over the damaged area. If good sealing properties are required then either a shrinkable tubing with internal coating of glue or self-vulcanizing tape p/n 3540116-5 must be used.