Tying knots in an extension cord is a quick way to shorten their life.
While it is tempting to tie two cords together to keep them from disconnecting or to knot one around itself to keep it from tangling while stored, this knotting causes the individual conductors to eventually break, reducing the current carrying capacity of the cable.
Because the outside diameter of a knot is greater than the inside diameter, the outside conductors are stretched and the inside conductors are compressed, both actions put too much stress on small individual wires.
The greater the number of conductors in an extension cord, the easier it is to coil, but greater numbers mean smaller individual diameters for each strand, making it more likely to be damaged when a knot is tied.
Instead of knotting, use some tie line or Velcro cord wrap.
Harrison Bros. Inc.