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All but the very oldest BX cable had a flat bonding conductor inside
that was to be used, NOT the sheath.


** FYI, AC cable was invented at the turn of the century by Gus Johnson and
Harry Greenfield. "BX" was never a code designation, just a name given to AC
cable made by GE's Sprague division. The bonding conductor wasn't required
until the 1959 Nec and was never used as a ground, only to assure a clean
grounding path against the metal coils of the sheath