BX cable is a metal-armored electrical cable used in both residential and commercial projects. A spiral-wound steel sheath protects the plastic-insulated conductors inside, and the armor itself can carry the grounding path when it lands on a metal box, something NM cable cannot do. That combination makes BX the default choice for exposed runs, damp basements, and appliance circuits where a hard outer shell earns its keep. Dryers and ranges pull heavy current, so the three-wire versus four-wire hookup decision for those circuits depends on the cable and receptacle you install.
What BX Cable Is
BX is shorthand for armored cable, sold under several names: armored cable, type AC, MC cable, Greenfield, and flexible metal conduit. All share the same architecture: insulated conductors wrapped in a continuous metal sheath that shrugs off impact and offers a path to ground. In the wiring methods that include NM cable, MC cable, and conduit systems, armored cable sits between unprotected Romex and rigid pipe on both cost and protection.
Names and Trade Designations
Type AC, armored cable, uses a thin aluminum bonding strip inside the armor as the grounding conductor. Type MC, metal-clad cable, carries a separate insulated ground wire in the bundle. Greenfield is the old trade name for flexible metal conduit, a hollow raceway you thread wires through rather than a factory-assembled cable. The BX label dates to the 1920s, when one manufacturer used it as a trade name; the term stuck as the generic job-site word for armored cable long after the trademark lapsed.
How the Cable Is Put Together
Inside the steel shell, each conductor carries its own thermoplastic insulation, and the bundle is wrapped in paper or fiber before the armor goes on. The sheath is wound in a continuous helix, which is why the cable bends freely along its length but resists sharp kinks. That helix also lets the armor serve as a grounding conductor in type AC, because the interlocking steel stays in contact with itself and with the connector at each box.
Where to Use BX Cable
Armored cable earns its place where plastic-sheathed cable is not allowed or not wise. Exposed runs in garages, unfinished basements, and utility rooms benefit from the steel jacket, because a stray nail or a bumped box hits metal instead of insulation. Local codes in some jurisdictions require metal raceways or armored cable for nearly all residential wiring, which keeps BX common in those markets.
Typical Installations and Code Drivers
- Dryer, range, and water heater circuits where a metal appliance needs a reliable grounding path to the box
- Unfinished basements and garages where cables run exposed across framing
- Commercial and multifamily buildings where local codes restrict NM cable
- Short runs between a panel and metal junction boxes where the armor provides the equipment ground
Durability is where BX separates from NM. The steel sheath resists punctures, impact, and rodent damage that would destroy a plastic jacket, and the conductors stay protected even when the outer surface gets scuffed. The trade-off is weight and stiffness: BX is heavier per foot, harder to coil, and unforgiving in tight spaces, so it suits runs where protection matters more than speed. Type MC with a wet-rated jacket can run in damp and wet locations, while type AC is limited to dry locations; the distinction matters in basements, crawl spaces, and outdoor runs where moisture would attack an NM jacket.
Repurposing Scrap Cable
Leftover offcuts are useful around the shop because the bendable armor holds whatever shape you give it. A short length becomes a flexible flashlight stand made from scrap cable, which aims light at a work area without tying up a hand. The same stiffness that makes BX awkward to coil makes it handy for temporary supports, fixture hangers, and small shop jigs.
How to Rip and Cut BX Cable
Cutting BX is the step that separates experienced electricians from novices, because the armor can easily nick the conductors inside. The trick is to cut the steel shell without touching the wires. A hacksaw works, but the blade must run at a shallow angle so it scores the sheath rather than sawing through it. A rotary armored cable cutter does the same job in one pass. Choosing the right tool follows the same logic as picking coaxial cable cutters for clean signal cable termination: match the blade to the jacket, cut from the outside, and keep the cutting edge away from the conductors.
Tools for Cutting Armored Cable
- Hacksaw with a fine-tooth blade for occasional cuts
- Rotary armored cable cutter that scores and snaps the sheath
- Armored cable stripper with a depth stop for production work
- Side cutters and pliers for trimming the bonding strip
Step-by-Step Ripping Process
- Measure and mark the armor at the cut point, allowing extra conductor length inside the box.
- Score the steel with a hacksaw at a shallow angle, cutting only the sheath and not the insulation beneath.
- Twist and snap the armor at the score line, or run a rotary cutter around the circumference.
- Pull the conductors free and fold the sharp cut edges back, or cover them with an anti-short bushing.
- Dress the aluminum bonding strip in type AC back over the cut so it contacts the clamp inside the box.
The cut edges of the armor are razor sharp, so wear gloves, de-energize the circuit before working near it, and install an anti-short bushing at every termination. A bushing costs pennies and prevents the sharp steel from slicing into conductor insulation when the cable shifts inside the box.
Installing BX Cable: Fittings and Fishing
Armored cable connects to boxes with clamps and connectors made for the sheath, never with the plastic staples used for NM cable. The clamp must bite the steel and, in type AC, grip the bonding strip so the ground path continues through the box. Leave at least 6 inches of conductor inside each box, the working allowance that code requires.
Fittings, Clamps, and Connections
Two-hole straps and nail-on clips hold BX to framing. At the box, an anti-short bushing protects the conductors from the cut edge of the armor, and the connector locks the sheath in place. BX bends, but it has a minimum radius; plan runs with gradual curves instead of sharp corners, because kinking the armor weakens the sheath and can damage the conductors inside.
Fishing Through Finished Walls
Running armored cable through finished walls is harder than NM because the steel sheath does not flex around corners. Wire fishing tools and techniques such as fish tape, glow rods, and magnetic pullers help route the cable through wall cavities. Leave extra bend radius at every corner, pull slowly to avoid scuffing the armor against stud edges, and never use the conductors themselves as a pulling grip.
BX vs. NM Cable: Choosing the Right Wiring Method
The most common question about BX is how it compares with NM cable, the plastic-sheathed product most homeowners know as Romex. NM is cheaper, lighter, and faster to install, but its jacket offers little physical protection and it cannot carry the ground path through its own sheathing. BX trades money and labor for armor, a built-in grounding path, and approval for exposed locations.
Armored vs. Plastic-Sheathed Cable
| Feature | BX armored cable | NM cable |
|---|---|---|
| Outer sheath | Spiral-wound steel armor | Flexible PVC jacket |
| Grounding path | Armor plus bonding strip in AC, internal ground in MC | Separate bare ground wire |
| Exposed runs | Allowed in most jurisdictions | Must be concealed |
| Relative cost | 25 to 50 percent more than NM | Lowest per-foot cost |
| Cutting | Armor cutter or hacksaw | Utility knife |
What BX Costs in Practice
The price gap narrows when you count the whole installation. Armored cable saves the cost of conduit and fittings in exposed locations, and type AC eliminates the separate grounding conductor. When you price a job, compare the complete system rather than the cable alone, and weigh the NM cable vs. THHN buying decisions that determine whether you pull wire through conduit or lay factory-assembled cable.
Common sizes cover the same circuits as NM. The 14/2 cable handles 15-amp lighting and receptacle circuits, 12/2 serves 20-amp kitchen and bath circuits, and 10/2 or 10/3 feeds 30-amp dryers and water heaters. Ampacity follows the conductor gauge exactly as in any other wiring method; the armor adds protection, not capacity.
Durability, Grounding, and Code Compliance
The steel armor protects conductors from punctures, impact, and rodents over decades of service, which is the main reason BX keeps its share of commercial and exposed residential work. Service life depends on the connections as much as the cable: a loose clamp or a missing bushing ages faster than the steel sheath itself.
Keeping the Ground Path Intact
Every connection point matters. Clamps must bite into the steel sheath, the bonding strip in type AC must be dressed back over the cut edge so it contacts the connector, and continuity must be verified between each box and the panel before the circuit goes live.
Grounding is where armored cable earns its keep, because the metal path from panel to box protects people when a fault occurs. Review the electrode, conductor, and bonding requirements for grounding systems before final inspection, then confirm continuity with a multimeter rather than trusting a visual pass. BX is not the right answer for every circuit: for short exposed runs, appliance circuits, and metal-box layouts it beats NM on protection and beats conduit on labor, while long concealed residential runs still favor cheaper NM. Match the wiring method to the installation, and let the code book settle the arguments.