When doing electrical projects on your home, you often encounter a type of metal-clad wiring called BX. BX wiring is not just a vestige of the past. Even with new projects, you still have the choice of using either BX wire or NM wiring (non-metallic sheathing).
Let us take a brief but comprehensive look at BX wire, its pros and cons, and how it performs against its newest competitor, NM wire.
BX Wiring: In Brief
Going under various names--BX, metallic sheathed cable, type AC, MC, or armored cable--BX is a collection of plastic-coated insulated wires (typically 14- or 12-gauge), bundled together and protected by a ribbon-like metal sheathing.
BX is contrasted with a newer wire, NM, which stands for "non-metallic." Instead of the metal sheathing, NM has a slick vinyl covering that is easy to rip and to pull through holes in studs. Romex is one popular brand of NM.
A chief distinction between BX and NM is that BX can achieve grounding through the outer metal casing. This casing needs to be attached to metal boxes.
Can BX Ever Go Bad and Should It Be Replaced?
Like any other cable, if the 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 well-placed nail or screw.
Wires within the armor may display degradation of their rubber insulation. However, this may just be at the ends. If you rip back the armor, 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.
BX vs. NM Wiring
|BX Wire||NM Wire|
|Ripping||Difficult without special tool costing $30-$40||Less difficult but still, a cheap cable ripper is recommended.|
|Cost||$56 for 100 ft. of 12/2.||$35 for 100 ft. of 12/2 Romex brand.|
|Handling||Heavy, difficult to run through studs.||Lightweight. The slippery coating makes cable easy to pull through holes in studs.|
|Safety||Safer, as the metal armor protects well against accidental penetrations.||Less safe, as the vinyl sheathing is easily penetrated.|
|Grounding||Cable grounded via its metal armor or internal green plastic-coated ground wire.||Because vinyl is not conductive, grounding is achieved by a separate bare copper ground wire in the bundle.|
|Cutting||Cut with a hacksaw.||Cut with a lineman's pliers.|
Which Do You Recommend: BX or NM?
As a do-it-yourself residential electrician, you will find it easier to handle, rip, and pull NM wiring.
How Do You Rip It?
There are two methods.
- Without Special Tool: You can cut the outer armor with a hacksaw, assisted with a very strong pair of wire snippers or pliers. With this method, though, it is very easy to nick the insulation on the inner wires--not to mention lacerating your fingers on the sharp metal armor.
- With Special Tool: If you think you will be doing a lot of cutting, invest in a cutter, such as the Roto-Split.
When Was BX Developed?
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.
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, but it may have something to do with the product first being produced in the Bronx, New York.