A BX cable is an older, commonly used term for Armored Cable (AC), a type of electrical cable characterized by its flexible metal sheath providing robust physical protection for the electrical conductors inside.
Understanding BX Cable
Historically, "BX" became a proprietary name for Armored Cable, originally manufactured by the Sprague Electric Company. Over time, it evolved into a generic term for any flexible metal-clad electrical cable. These cables are designed to house and protect individual insulated wires, ensuring they safely deliver electricity from an electrical panel to various devices such as outlets, switches, and light fixtures. Its primary purpose is to provide a durable and protective pathway for electrical wiring, especially in areas where the wiring might be exposed to physical damage.
Key Features and Benefits
BX cables, or Armored Cables, are distinguished by several characteristics:
- Metal Sheath: They feature an outer layer typically made of spirally wound galvanized steel or aluminum armor, which gives the cable its distinctive appearance and offers significant mechanical protection.
- Conductors: Inside the armor, individual insulated copper or aluminum conductors (hot, neutral, and sometimes a grounding conductor) are bundled together, often wrapped with a paper or fibrous material.
- Bonding Strip: Traditional BX cables (AC) usually contain a bare aluminum bonding strip that runs the length of the cable, serving as an equipment grounding conductor by making contact with the armor.
- Durability and Protection: The metal cladding makes these cables highly durable and resistant to punctures, cuts, and rodent damage, which contributed to their popularity for homeowners in the past. This added protection is crucial for electrical safety and system longevity.
- Flexibility: Despite the metal armor, the spiral construction allows for a degree of flexibility, making installation around corners and through various structural elements feasible.
Common Applications
BX cable was a popular choice for a wide range of electrical installations, particularly in residential and commercial buildings constructed during the early to mid-20th century. Its applications include:
- Branch Circuits: Connecting power from electrical panels to lighting fixtures, receptacles, and switches.
- Exposed Wiring Runs: Ideal for locations where wiring is not concealed within walls, offering protection against accidental damage.
- Industrial Settings: Providing resilient wiring for machinery and equipment in environments prone to physical stress.
Evolution to Modern Standards: BX vs. MC Cable
While the term "BX cable" is often still used, the modern equivalent and successor is often referred to simply as Armored Cable (AC) or, more commonly, Metal-Clad (MC) Cable. While both are metal-clad, there are key differences reflecting advancements in electrical codes and materials:
| Feature | BX Cable (Armored Cable - AC) | Metal-Clad Cable (MC) |
|---|---|---|
| Grounding | Armor usually serves as ground with an internal bonding strip. | Typically includes a separate insulated grounding wire. |
| Outer Sheath | Spirally wound steel or aluminum. | Spirally wound steel or aluminum; may also be smooth or corrugated. |
| Inner Wrap | Often has paper or fibrous anti-short bushing required for termination. | Insulated conductors directly, no paper; anti-short bushing not always required. |
| Flexibility | Good | Often more flexible due to different armor designs. |
| Installation | Requires anti-short bushings to protect conductors from armor edges. | Easier termination; some types can be used in wet locations. |
| Code (NEC) | Article 320 | Article 330 |
For more detailed information on electrical wiring standards, refer to resources like the National Electrical Code (NEC) published by the NFPA.
Why Was BX Cable Popular?
BX wires are a type of metal-clad electrical cable that has been a popular choice for homeowners in the past due to its durability and added protection. During its prime, it offered a significant advantage over knob-and-tube wiring or early forms of non-metallic sheathed cable by providing a robust mechanical barrier against physical impact, abrasion, and potential rodent damage. This made it a reliable choice for ensuring the long-term safety and integrity of electrical installations in a variety of settings.
Modern Context and Replacement Considerations
While BX cable was once a staple, its "life cycle" in new installations has largely been superseded by modern MC cable and non-metallic (NM-B) sheathed cable, which often offer easier installation and more explicit grounding paths. However, many older homes still have existing BX wiring. When undertaking electrical projects, such as running electric cables from the electrical panel to new devices like outlets or switches, it's crucial to assess the condition of existing wiring. Homeowners might consider replacing older BX wiring if it shows signs of deterioration, has insufficient grounding, or does not meet current electrical code requirements for new installations or significant renovations.
