Q: Can extension cords be repaired?
A: Yes, provided the repairs restore the cord to its approved condition.
Electrical equipment and conductors, including extension cords, must be approved by a nationally recognized testing laboratory, such as Underwriters Laboratories Inc. (UL). If a cord is repaired, it must be able to meet the same performance and safety standards as it did originally. Superficial nicks or abrasions in the outer jacket of the cord that do not expose the conductors or the inner insulation, or changes the flexibility of the cord, do not need to be repaired.
Cords that are No. 12 American Wire Gauge (AWG) or less cannot be repaired and must be disposed of.
From Minnesota OSHA’s “Safety Lines” newsletter, Jan 2011.