in oregon the ADA disabilities requirement comes from a UBC building code section and the inspectors messure 15" from FF level to the bottom of the receptacle openings, both data-comm and line voltage... the switch heights are lot more complicated but mostly 48" to the top of the switch is maximum... 54" if you can parallel park your wheelchair next to the devices.... but usually the plans i see will say "AFF...to center" ... in practice though, we usually set receptacle boxes 18" AFF to centers
