According to a website it was 1959:
BX is the common trade name for AC. BX was the trademark of cable made by G.E.'s Sprague Electric division.
189?- Gus Johnson and Harry Greenfield patent AC
1910- AC receiving acceptance.
1920s or the early 1930s widespread adoption.
1932 NEC- Armored cable was officially called Type AC
1952- Aluminum clad AC introduced.
1959 NEC- Aluminum bonding wire required under metal sheathing.
