I would write the article to read something like this- "dwelling interior staircase landing with 6 or more risers in each direction shall have one receptacle outlet located on landing, or, within 6 feet of top riser and within 6 feet of bottom riser." I propose 6 or more risers to be consistent with 3 way switch requirements for stairs.
I propose this because dwelling units are generally not to have more than 6 feet of wall space from a receptacle outlet. Staircase risers may be as far as 20 to 30 feet from a receptacle outlet sometimes further in large custom homes. My cousin cleans homes for living and asked why no plugs are by stairs saying sometimes she has to roll out extension cord to vacuum carpeted stairs, and to dust and polish hardwood stairs and railings. I have also seen in homes with a large landing a table or stand placed at landing with some type of electrical appliance. Adding this requirement would make the use of cords on staircases less likely and would be safer.
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Robert B. Alexander, P.E.
Answers based on 2014 NEC unless otherwise noted.