ECN Forum Forums General Topics of the Trade General Discussion Area Strain relief on drop cords.

In an industrial setting. 30amp 480volt Flexible Drop cords to supply power to machinery. These Cords must have Strain relief at the top.
My question, must the twist lock plugs which are located 6' off the floor also have special strain relief built in?
400.10 in the 2002 NEC does not go into a lot of detail.
What's your take?
Thanks