When was bx cable invented

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Last updated: April 17, 2026

Quick Answer: BX cable was invented around 1905 by the General Cable Corporation, originally designed as an armored electrical wiring system for early 20th-century buildings.

Key Facts

BX cable was introduced in 1905 by General Cable Corporation
It was developed as a safer alternative to open wiring and knob-and-tube systems
The original BX design lacked a grounding wire, added later in the 20th century
BX stands for "Brooklyn Express" or "B-X" as a model designation
It became widely adopted in North American construction by the 1920s

Overview

BX cable, also known as armored cable or AC (armored cable), revolutionized electrical wiring in residential and commercial buildings during the early 20th century. Invented in 1905 by the General Cable Corporation, it provided a more durable and fire-resistant alternative to the then-common knob-and-tube wiring systems.

Designed to protect insulated conductors within a flexible metal sheath, BX cable improved safety and simplified installation in wood-frame structures. Its development marked a major advancement in electrical code standards and building safety regulations.

1905 introduction: BX cable was first introduced by General Cable Corporation as a response to the fire hazards associated with early electrical systems.
Flexible metal sheath: The cable's interlocking steel armor protected internal wires from physical damage and reduced fire risks in walls and ceilings.
No initial grounding: Early BX systems lacked a dedicated grounding conductor, a feature not required until electrical codes evolved in the mid-20th century.
Widespread adoption: By the 1920s, BX cable became standard in North American construction due to its durability and ease of installation.
Name origin: The term "BX" may derive from "Brooklyn Express" or simply as a model designation "B-X" used by manufacturers.

How It Works

BX cable functions by enclosing insulated electrical wires within a spiral-wound metal armor, providing mechanical protection and some degree of electromagnetic shielding. This design allows for secure, concealed wiring in walls, floors, and ceilings without requiring conduit.

Armor: The interlocking steel strip forms a flexible conduit around wires, preventing damage from nails, rodents, and abrasion during installation.
Insulated conductors: Typically two or three wires (hot, neutral, and sometimes ground) are individually insulated with rubber or thermoplastic materials.
Grounding strip: Modern BX includes a bonding strip or internal ground wire that runs alongside conductors for proper grounding compliance.
Connector fittings: Special clamps and connectors secure the cable to electrical boxes and ensure continuity of the metal sheath.
Fire resistance: The metal sheath resists ignition and contains sparks, enhancing safety in combustible building materials.
Installation flexibility: BX can be bent around corners and through tight spaces, reducing the need for junction boxes compared to rigid conduit systems.

Comparison at a Glance

The following table compares BX cable with other common wiring methods used in residential construction:

Feature	BX Cable	Knob-and-Tube	Non-Metallic (NM) Cable	Rigid Conduit
Introduced	1905	1880s	1920s	1890s
Material	Steel armor with internal wires	Ceramic knobs and tubes	Plastic sheathing	Galvanized or EMT metal pipe
Grounding	Yes (modern), no (early)	No	Yes (with ground wire)	Yes
Fire Resistance	High	Moderate	Low to moderate	Very high
Installation Cost	Moderate	Low (then), high (retrofit)	Low	High

While BX cable offered significant improvements over knob-and-tube wiring, it was eventually supplemented by non-metallic (NM) cable in the mid-20th century due to lower cost and easier installation. However, BX remains in use today in commercial and industrial applications where durability and code compliance demand armored protection.

Why It Matters

The invention of BX cable had a lasting impact on electrical safety and building standards, shaping modern wiring practices across North America. Its development reflected the growing need for reliable, enclosed electrical systems as homes and businesses adopted more electrical devices.

Safer installations: Reduced fire risk compared to exposed knob-and-tube wiring, especially in wooden structures.
Code influence: Helped shape the National Electrical Code (NEC) requirements for enclosed and protected wiring systems.
Urban electrification: Enabled rapid expansion of electrical infrastructure in cities during the 1900s–1930s.
Construction efficiency: Allowed electricians to run wires through framing quickly without installing separate conduit.
Legacy use: Still used today in areas requiring physical protection, such as garages, basements, and industrial buildings.
Historical value: Original BX installations are often found in early 20th-century buildings, valued for their durability and craftsmanship.

Though newer wiring methods have surpassed BX in residential popularity, its role in advancing electrical safety remains a cornerstone of modern building practices.