What is bx

Overview

BX is a widely recognized abbreviation in electrical contracting that refers to Type AC armored cable, a flexible conduit system designed to protect electrical conductors. The term originated as a brand name but has evolved into the industry's standard reference for this style of cable. BX cable consists of insulated electrical wires bundled together and wrapped in a flexible metal sheath, creating a robust protection system for residential and commercial wiring applications.

Origin and History

The history of BX cable dates back to the early 1900s when Edwin Greenfield and Gus Johnson developed basic armored cable technology. BX was first used around 1910 and experienced widespread production and adoption throughout the 1920s. During this period, it was promoted as a modern, safe, and fireproof alternative to the older cloth-sheathed wiring systems that dominated earlier electrical installations. The name 'BX' has remained in use for over a century, outlasting many other product naming conventions in the electrical industry.

Construction and Composition

BX cable features a distinctive construction that provides both protection and flexibility. The cable contains two or more insulated copper conductors that carry electrical current. These conductors are encased within a flexible metal sheath made from galvanized steel or aluminum. The metal armor is created by wrapping a metal strip in a helical or spiral pattern around the conductors, creating the cable's characteristic metallic snakeskin appearance. Modern BX cables also include an internal bonding strip to ensure proper grounding.

Technical Specifications and Code Designation

While commonly called BX, the electrical code technically designates this cable as Type AC (Armored Cable). The National Electrical Code recognizes BX as an approved wiring method for both exposed and concealed installations. The flexible metal armor serves as both protection and the equipment grounding conductor. The cable's flexibility allows it to bend and conform to installation requirements, making it practical for retrofit projects and complex routing scenarios.

Current Applications and Industry Use

Today, BX cable is commonly found in commercial and industrial applications, though residential use continues. It is particularly favored in installations where mechanical damage risk is high, such as basements, garages, utility rooms, and areas where the wiring might be exposed to impact or puncture. The metal sheathing provides superior protection compared to non-metallic cable, and the armor resists damage from nails, screws, and rodents. The shielding properties also help reduce electromagnetic interference and electric field emissions.