Also sometimes called an OSHA plug. It is my understanding that these cord ends were at one time required on all construction grade cords in California. I prefer them over the typical household grade cord ends as the ground tends to stay with the cord better. When inspecting construction sites it is almost always the household cord end configurations that are missing the ground. You will also find the locking cord ends on other amperages as well, simply because in order to plug into the construction site you have to have an adapter to go from locking to non-locking. The connections stay together better as well with all the cord dragging that goes on.
Nice links Bjarney, The Hubbell system looks good and expensive. I have never seen a job site with anything like that in MA, RI, NH.
I am sure there must be some, but SER and NM is what is used for temps here for the majority of jobs.
Typical temp power distribution for around here, 480 service, distribute 100 amps 480 with SER to each, or every other floor to a transformer, 208/120 panel mounted to transformer branch circuits from there with NM.
Bob Badger Construction & Maintenance Electrician Massachusetts