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Last updated: April 8, 2026

Quick Answer: BX cable, also known as Armored Cable (AC) or Metal Clad (MC) cable, is generally not permitted for use within residential dwelling units in the United States according to the National Electrical Code (NEC) for new installations, though exceptions may apply for specific renovations or older installations that were grandfathered in. Modern residential wiring typically employs non-metallic sheathed cable (NM-B), commonly referred to as Romex, due to its flexibility, ease of installation, and lower cost.

Key Facts

BX cable (AC/MC) is typically not allowed for new residential wiring in dwelling units per NEC.
Non-metallic sheathed cable (NM-B/Romex) is the standard for residential wiring in the US.
Older installations of BX cable might be grandfathered in and permissible.
BX cable offers greater physical protection than NM-B cable.
Cost and installation difficulty are key reasons BX is less common residentially.

Overview

The question of whether BX cable can be used in a house is a common one for homeowners and DIY enthusiasts. BX cable, a term that often encompasses both Armored Cable (AC) and Metal-Clad (MC) cable, is a type of electrical wiring that features a flexible metal conduit enclosing insulated conductors. Its primary advantage lies in its robust physical protection, making it suitable for environments where the wiring might be exposed to damage, such as in commercial or industrial settings. However, its application within residential dwelling units is more restricted.

In the context of residential electrical installations in the United States, the National Electrical Code (NEC) generally favors the use of non-metallic sheathed cable, commonly known by the brand name Romex. This preference stems from a combination of factors including ease of installation, flexibility, and cost-effectiveness. While BX cable offers superior protection against physical damage, its rigidity and the specialized tools required for its installation can make it more challenging and expensive for typical home wiring projects. Understanding these distinctions is crucial for ensuring code compliance and electrical safety.

How It Works

Physical Protection: The defining characteristic of BX cable is its metallic armor. This flexible metal conduit is designed to protect the insulated wires within from physical damage, such as punctures, crushing, or impact. This makes it a more durable option in environments where wiring might be more susceptible to abuse.
Grounding: Historically, the metal armor of certain types of BX cable (specifically AC cable) also served as the grounding conductor. However, modern codes often require a separate ground wire for enhanced safety and reliability, especially with MC cable. This dual grounding mechanism is a key safety feature, though it adds complexity.
Installation Method: Installing BX cable involves a different set of techniques and tools compared to flexible cords or non-metallic cables. It requires specialized connectors, benders, and cutters to properly terminate and secure the cable to boxes and enclosures. This can be more time-consuming and requires a certain level of skill and familiarity.
Cost and Availability: BX cable is generally more expensive than its non-metallic counterparts. Its specialized nature also means it might not be as readily available in smaller quantities at all hardware stores, compared to standard Romex. This can contribute to higher overall project costs for residential applications.

Key Comparisons

Feature	BX Cable (AC/MC)	Non-Metallic Sheathed Cable (NM-B/Romex)
Physical Protection	High (metal armor)	Moderate (plastic sheath)
Installation Ease	More difficult, requires special tools	Easier, more flexible, less specialized tools
Cost	Higher	Lower
Typical Use Case	Commercial, industrial, exposed areas	Residential dwelling units, interior walls
Grounding Method	Armor may act as ground (AC), separate ground wire often required (MC)	Dedicated ground wire

Why It Matters

Code Compliance: The primary reason for the distinction lies in the National Electrical Code (NEC). While the NEC permits BX cable in certain applications, it specifically designates non-metallic sheathed cable as the preferred and often mandatory choice for wiring within the walls, floors, and ceilings of residential dwelling units. Deviating from these code requirements can lead to failed inspections, safety hazards, and insurance issues.
Safety Considerations: While BX cable offers excellent physical protection, improper installation can introduce safety risks. For instance, if the metal armor is not properly grounded, it can become energized in the event of a fault, posing a shock hazard. Furthermore, the stiffness of BX cable can make it more challenging to route through tight spaces without damaging other building components or the cable itself, potentially leading to future issues.
Cost-Effectiveness for Homes: The significantly lower cost and greater ease of installation associated with NM-B cable make it the most economically viable option for the vast majority of residential wiring needs. The cost savings on materials and labor for a typical home rewire or new build are substantial when using Romex. This cost factor is a major driver of its widespread adoption in the residential sector.

In conclusion, while BX cable serves important roles in electrical installations, its use within typical residential homes is generally discouraged and often prohibited by modern electrical codes for new work. The focus remains on NM-B cable for its balance of safety, cost, and ease of installation, ensuring that residential electrical systems are both functional and code-compliant. Always consult with a qualified electrician and local building codes to ensure your electrical work is safe and legal.