A short, and by no means exhaustive, history of residential receptacle requirements, at least as far back as my NEC collection goes:
1940: One receptacle for every 20 linear feet of wall space. At least one receptacle for laundry appliance.
1947: Laundry area shall have at least one three-wire receptacle, with the third contact reserved for equipment grounding.
1951: NEC Handbook becomes more specific as to the precise type of three-wire receptacle required in laundry area; includes illustration of what we now call a 5-15R.
1956: One receptacle required for every 12 linear feet of wall space.
1959: No point along the floor line of usable wall space more than 6 linear feet from a receptacle. The receptacle closest to the kitchen sink must be of the grounding type. No receptacles are required outdoors or in the garage, but if installed, they must be of the grounding type.
1962: All 120V and 240V 15A receptacles, in all occupancies, to be grounding type.
1971: A kitchen counter space 12" or wider requires a receptacle. Receptacles rendered inaccessible by fixed appliances do not count as meeting the minimum requirements of 210-22(B).
1975: At least one receptacle required in each of the following locations: bathroom, adjacent to the sink; outdoors if single-family home; basement; attached garage. All 120V 15A and 20A receptacles in bathrooms and outdoors require GFCI protection.
1987: Each receptacle within 6' of the kitchen sink is required to have GFCI protection.
1990: Receptacles serving kitchen countertops are required to be spaced no more than 48" apart, so that no point along the backsplash is more than 24" from a receptacle (excluding areas behind sinks and ranges).
1996: All receptacles serving kitchen counters to be GFCI protected.
[This message has been edited by yaktx (edited 02-15-2007).]
