In the late 1800s and early 1900s, one of the earliest wire raceways was called “moulding” (sic).
It consisted of two pieces of wood, a backing and a capping. The backing had two or more individual grooves, one for each wire, and a capping to cover the grooves. The grooves separated the wires by 1/2 inch, and provided mechanical protection.
Although wood moulding was not intended for use in concealed spaces or damp locations, it was required by the National Electrical Code® (NEC®) to have two coats of waterproof paint, or be impregnated with moisture repellant. This product continued to be permitted by the NEC until the 1935 edition. However, by the mid-1910s, some large cities had banned its use, and wood moulding was being phased out as metal moulding and armored cable were becoming widely available.
Armored cable was first Listed by Underwriters Laboratories Inc. in 1899 for Sprague Electric Co. of New York, and was originally called “Greenfield Flexible Steel-Armored Conductors,” after one of its inventors, Harry Greenfield. Armored cable first appeared in the 1903 NEC.
There were originally two initial versions of this product, one called “AX” and the other “BX,” with the “X” standing for “experimental.” The “BX” version became the one that eventually was produced, and hence the name “BX” stuck. This was the registered trade name of armored
cable for General Electric (GE), who later acquired Sprague Electric. Armored cable made after 1959 requires an aluminum bonding strip under the armor to help improve the conductivity of the armor. This continues to be a popular wiring method today, and is described in Article 320 of the NEC.
Published in the U/L “Electrical Connections” column