BX wire serves as its conduit, whereas Romex requires a conduit if used outside of finished walls or used outside. At this point, new installations need to be inspected before permission is granted to install devices on the cables. If you add a project to existing wiring, ensure that power in all branch circuits is off.
What is Romex Wire & NM Cable?
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While ill-placed nails or screws can pierce the armor, romex vs bx it remains stronger than the vinyl covering on non-metallic (NM) cables. Over time, the wires within the armor may exhibit degradation of their rubber insulation, but this is often limited to the exposed ends. A lot of brand names are involved, but there are a few standard initialisms in the industry that are used by the two main manufacturers of MC and AC cable. For example, MC-PCS cable can include a power control signal on a separate wire, often for controlling lighting. MC IG cable is designed to carry multiple insulated ground wires, useful for when separate, isolated, or redundant ground paths are required, such as when supplying power to medical equipment. In fact, health care facility equipment accounts for a lot of the special-use cables.
However, if you rip the metal sheathing back, you’ll find that the insulation is in good condition. In Part One I discussed knob and tube wiring and the potential problems and issues that may arise if your home still contains legacy knob and tube. Perhaps your home still contains knob and tube, or you are considering remodeling or planning new construction. In this article, I will explain current options and residential wiring best practices. I will also explain the pros and cons for the two most popular wiring types, Romex and BX, and why I ALWAYS use BX in any new wiring I install myself and insist it is used in any project in which I am managing or consulting.
Plus all the wires needed for a circuit are right there together in one neat package. For example, the earliest versions didn’t include a bonding wire (they used only the armor for a ground path), so its armor could get dangerously hot in a fault condition. The reason for this seems a little arcane, but is actually straightforward enough.
Since MCAP terminates similarly to BX, we can use that figure as a general reference for comparing MC to BX/AC cable. BX wiring comprises plastic-coated insulated wires (usually 14-gauge or 12-gauge) bundled together and safeguarded by a ribbon-like metal sheath. At first glance, the metal sheathing appears to be a single-ribbed tube.
Romex vs AC (BX)
Although BX wiring has been extensively used, it remains a viable option for modern projects, offering unique benefits that make it a more suitable choice than NM cables. Many of my concerned clients have spent a lot of effort and money to shield against and reduce their exposure to electric fields. Some even go as far to turn off the circuits to their bedrooms when they sleep to reduce their exposure.
Old House Journal
The plastic used is resistant to moisture and microbes and is very durable. The plastic sheathing also has a very high melting point thus is heat and flame resistant. Splices are done in junction boxes, thus protected from the elements and pests.
Fine Home Building
This prophylactic measure is an excellent way to continue a prudent hygienic practice. Since the metal edges are always sharp, you should caution while cutting. It’s also essential to inspect the interior insulation to ensure that gashes or nicks expose no conductor.
BX cable is, naturally, rodent-resistant, so if your home is in the country and therefore prone to mice — or if your spouse keeps beavers as pets — you might consider the protection of BX cable. These same properties might make BX beneficial for use by audiophiles, as well. First, because BX cabling provides a metal-clad covering for the electrical wires and is grounded, your electrical fields can be many times lower than the flux of the electrical fields emitted by unshielded Romex cable. On the other hand, a cable labeled ’12-3 with ground’ has 12-gauge wires, a copper grounding wire, and three conductors. You then turn the handle to make the cutting wheel cut away the metal sheathing.
- The cable jackets are color-coded to permit identifying the cable sizes quickly—black jacket for #6 and # 8 AWG, orange jacket for # 10 AWG, yellow jacket and red jacket for # 12 AWG, and white jacket for # 14 AWG.
- One final distinction is that MC cables don’t have a limited number of conductors they can contain, while AC cable can contain no more than four insulated conductors.
- MC cable must be supported every 4.5 feet and AC every 6 feet, except in a few special circumstances.
- WesBell Electronics, for example, basically says AC, BX, and MC are all equivalent.
- One added benefit of NM cable over knob and tube is that knob and tube emits fairly high levels of low frequency alternating current magnetic fields, due to the separation of the hot and neutral conductors.
What all of this means is that MC cable is more flexible and easier to use. It now comes in varieties that use the armor as a ground path, and varieties that include multiple grounding conductors for redundant applications and other purposes. Anywhere NM cable is not allowed, or must be run through conduit, some version of MC cable can be used, and this is not true of AC.
When it comes to residential wiring, choosing the right cable is crucial for ensuring safety, functionality, and long-term reliability. Two of the most common options are NM Cable (Non-Metallic Sheathed Cable) and BX Cable (Armored Cable). Though both serve to transmit electricity, their structural differences and ideal use cases set them apart significantly. Below, we dive deep into their characteristics, advantages, and applications to help homeowners and contractors make informed decisions. However, wires in the armor may show degradation of rubber insulation, more so at the exposed ends.
If a credible company like WesBell, which has sold wire and cable to its customers for 34 years, gets some details wrong, how can a layman hope to get a handle on it? In fact, very few resources we looked at got all the details right, and because the National Electrical Code doesn’t specifically name or define BX cable, it’s difficult to adjudicate all the confusion with absolute certainty. The other day, I was consulting for a new home being built in Old Westbury, Long Island, New York.
- The armored casing makes it also much more difficult to cut and to work with by hand using side cutters or a hacksaw, but easier accomplished with a special armored cable cutting tool.
- If your old BX cable is in good condition and can still manage to carry higher power demands, you’ve no reason to replace it.
- The other day, I was consulting for a new home being built in Old Westbury, Long Island, New York.
- Although Romex or NM cables come in different wire gauges, most households will require a 14-gauge or 12-gauge wire having either three or two conductors inside.
- Yesterday, I mentioned that my dream is to build our family’s home someday and install BX cable and fiber-optic light pipe into the walls.
Because of the difficulty in making a fair apples-to-apples comparison, homeowners understandably struggle with unpuzzling cost comparisons when electrical cable is involved. At Home Depot, 250 feet of Southwire 12/2 solid copper, aluminum-armored BX cable costs $198, while the same MC cable costs $199. Wholesale prices aren’t readily available for Southwire BX and MC, but the Atkore pricing difference is less than $8 for MC versus BX cable.
Why you may not need BX cable at all
And if you ask for help, 17 licensed electricians will immediately tell you that you’re going to burn down your house unless you stop asking questions and hire a professional. However, it should be avoided in high-risk areas where cables could be exposed to physical or environmental damage, as it lacks the robustness needed for such conditions. Although Romex or NM cables come in different wire gauges, most households will require a 14-gauge or 12-gauge wire having either three or two conductors inside. As soon as the cut is complete, grab the cable jacket below and above the cut and then twist it sharply.
If construction, remodels and renovations are done with BX, the electric field exposure is significantly reduced. The cost is greater, but for a 250-foot roll of BX, it is only about $30 more expensive than NM cable. So for a small job, the extra cost may only be $100 or so, and even for a large job the extra cost should not exceed $1,000. The armored casing makes it also much more difficult to cut and to work with by hand using side cutters or a hacksaw, but easier accomplished with a special armored cable cutting tool. Brought around in the early 20th century for residential and commercial use, BX or armored cables can still be found in older homes made of different materials and of varying concepts.
There are many other ways to look at the question of BX cable’s comparative cost-effectiveness, including factoring in the potential use of NM, the cost of fittings required for BX, etc. The outer sheathing for a Romex cable is a 30 mil-thick PVC jacket that protects and bundles individual wire conductors. It is beneficial to withstand the stress impacted on the sheathing when you pull the cable through holes. The most notable distinctions include the use of armor as a ground path, the protective sheathing material, and their suitability for outdoor use in damp locations. However, upon opening a wall or ceiling, you may come across the ribbed metal-clad BX cable, which may be preferred in certain situations.