BX Cable: What It Is and How to Use It

While widely used in the past, BX cable is hardly relegated to the past. With most electrical projects, you can use either metal-armored BX cable or plastic-sheathed NM cable.

BX cable is required when a metal box must be grounded to the cable's sheathing—NM cannot do this. Also, BX cable can be installed in some exposed locations, Learn the origins of BX cable, where to use it, its pros and cons, and how to work with it.

What BX Cable Is

Going under alternative names such as metallic sheathed cable, type AC, MC, Greenfield, or armored cable, BX cable is a collection of plastic-coated insulated wires (typically 14- or 12-gauge), bundled and protected by a ribbon-like metal sheathing.

BX's metal sheathing looks like a single, ribbed metal tube. However, the sheathing is a metal strand that runs in a helix-like or twisted manner around the wires.

BX is contrasted with a newer cable, NM, which stands for "non-metallic." Instead of the metal sheathing, NM has a smooth vinyl covering that is easy to rip and pull through holes in studs. Romex is one popular brand of NM electrical cable.

Where to Use BX Cable

BX cable can achieve grounding through the outer metal casing. This casing needs to be attached to metal boxes. NM cable's vinyl sheathing cannot ground a device, so a bare copper wire runs through every NM cable for grounding.

Some types of BX cable can be installed in exposed locations, either indoors or outdoors. NM cable and wiring must always be installed in an enclosed location (typically within a wall, ceiling, or under a floor).

BX Cable Durability

If the BX armor is nicked, cut, or shredded, the wires inside can be compromised. BX's armor, while much stronger than NM's vinyl, can still be pierced by a determined and ill-placed nail or screw. However, except for electrical wires that run through rigid metal conduits, no other type of electrical cable has as strong an outer casing as BX cable.

Wires within the armor may display degradation of their rubber insulation. But this may just be at the exposed ends. If you rip back the metal sheathing, you may find that the insulation is still good.

If old BX wiring is in good condition and can carry today's higher power demands, there is usually no reason to replace it. Unlike the older knob-and-tube wires from the early 20th century, the wire sheathing will not turn gummy and degrade over time.

BX Cable vs. NM Electrical Cable

As a DIY electrician, you likely will find it easier to work with NM electrical cable than BX cable. Unless the job specifies BX cable, use NM plastic-sheathed wiring.

NM wire is lightweight, easy to handle, and inexpensive. It's simple to cut, rip, and strip, plus it pulls effortlessly through holes in studs.

BX cable is heavy and its surface is corrugated, making it difficult to pull through the holes in studs. BX cable's metal sheathing can be hard to cut without nicking or severing the inner wire.

NM cable presents the danger of nicking inner wires. So, NM cable always needs to be protected. Running NM cable through holes drilled in the center of wall studs is one way to protect the cable.

Home improvement stores usually carry BX cable, though you'll find more choices of NM or Romex cable.

How to Rip and Cut BX Cable

Rip or cut the outer metal armor of BX cable with a special BX cutting tool or with another cutting tool like a hacksaw, pliers, or snippers.

BX Cutting Tool

For more than the occasional BX cutting or ripping, invest in a special BX cutter, such as the Roto-Split. This tool costs between $30 and $50 and makes the job of splitting and ripping back BX cable far easier and safer than by hand.

After you insert the cable into the tool's groove, you turn the handle to cause the cutting wheel to cut away the metal sheathing. The tool is calibrated to cut the metal but stops short of touching the inner wires.

Hacksaw, Snippers, Pliers

It is possible to cut and rip the armor without a BX cutting tool. You can cut the outer armor with a hacksaw, assisted with a strong pair of wire snippers or pliers.

With this method, there is the danger of nicking the insulation on the inner wires, not to mention lacerating your fingers on the sharp metal armor.

BX Cable Origin

BX is one of the earliest types of electrical cable developed for both residential and commercial uses in the early part of the 20th century.

Early forms of BX can still be found by homeowners renovating their homes. It is not certain how the term "BX" came to represent metal-armored cable. Some speculate that "BX" may be related to the product first being produced in the Bronx borough of New York.

Early accounts of BX cable being used date back to 1910. Widespread production and use of BX cable began in the 1920s when BX was promoted as being a modern, safe, fireproof improvement over older cloth-sheathed wiring.