by George W. Flach, Electrical Consultant, New Orleans, LA
Prevailing misconceptions about the present-day armored cable most likely
stem from imperfections inherent in the original BX. Improvements made in the product are
readily apparent when today's armored cable (right) is shown side-by-side with the old BX.
Today's armored cable, historically known as BX and more correctly as Type
AC, has proved to be a safe, reliable, and economical wiring method. However, there
continue to be restrictions, and sometimes prohibitions, on its use in many areas. What is
behind such restrictions and are they warranted?
These restrictions on the use of armored cable, for the most part, are the
result of years of misconceptions. Today, many electrical inspectors are reconsidering
their position on armored cable because of its long safety record, NEC recognition, and
improvements made since its introduction.
Basic armored cable was developed in the early 1900s by
and Gus Johnson, who called their product BX cable. It has become a generic term for all
armored cable. Some of the prevailing attitudes about the product most likely stem from
imperfections inherent in the original BX.
For instance, the Type R rubber insulation used was subject to
thermal-aging and cracking. The cotton-braided covering on conductors and overall braided
or paper covering did little to prevent moisture damage to the insulation. When the
bonding wire was finally added, it was flat and subject to breakage. In addition, it (and
even the armor itself) was often mistakenly used as the neutral conductor.
The biggest problem was the lack of proper cutting
tools. Old cutting methods, such as hacksaws or pliers for crimp cutting or twisting and
breaking the steel armor, were very unsatisfactory and often led to nicks on the
insulation and conductors, creating circuit opens or shorts.
As a result of these past deficiencies, the excellent safety record of
armored cable attested to by decades of NEC recognition has been ignored. Improvements
including newer, safer materials and expanded, application-oriented products, too often
have gone unnoticed. The progress in the performance of armored cable is a direct result
of changes made in its construction and installation techniques.