you were saying cogar...... 
I was gonna say that electricians screw it, crimp it, grommet it, solder it, nut it, ….. not knot it.
UL has a check-list a mile long and if any on the list applies to your product then you best apply it or you won’t get a UL sticker for it.
HA, and just what purpose does this knot serve?
On a more serious note, most every company that produces electrical equipment/devices has a full-time engineer for dealing with UL requirements.
Anyway, every device that has a “pluggable” electric cord should have said cord “restrained” within the device to prevent the “user” from pulling the electrical connection apart resulting in a potential “short” (electrical shock, fire or tripped breaker). Thus when a large-enough knot is tied in a lamp cord it provides said “restraint”.
And ps: don't put a new lamp cord on (re-wire) without tying a knot in the cord on the inside of the "hole "where it enters the base of the lamp ..... or in the cord that is on the inside of the light socket itself. The cord for a multi-bulb lamp has to be restrained somewhere within the base of the lamp.
