Romex® NM-B Cable
About Romex® NM-B Cable
Romex® from Southwire is a wide-reaching electrical wire used in several types of dry indoor wiring applications, mostly for homes and small businesses. It is available in many different configurations and sizes and offers a special jacket design that makes it easy to pull through conduit. And when you buy from WesBell, you get exceptional customer service and cut-to-order services to make it easy to select and install your Romex® cable.
Let’s take a closer look at Romex® wire and where it’s most useful.
What Is Romex® NM-B Wire?
Before we get too far into specifics, let’s break down the different parts of the name. Romex® is a brand name created by Southwire, a trusted provider of wires and cables. Romex® NM-B is mostly for residential branch wiring — the “B” in the acronym refers to its use as a branch circuit wire. You may also hear Romex® called SIMpull®, which is another trademark of Southwire and signifies the jacketing they use to make it easy to pull through conduit.
“NM” refers to a nonmetallic sheath. Before Southwire acquired the brand, Romex® was originally wrapped with braided cotton. It was modified later on and given a polyvinyl chloride (PVC) covering. The non-metallic nature of Romex® NM-B by Southwire initially proved to be a disadvantage, as it was very sensitive to heat, water and physical damage. But, with the right covering, it makes for a very useful wire in interior walls, garages and above-ground surface wiring applications. It’s commonly used to run power from the electrical panel to the lights and appliances throughout a particular home or building.
This cable is specified as non-metallic because it has a PVC jacket and is used indoors only. Metallic Cable, or MC cable, uses an aluminum interlocked armor for a jacket because it also works as a conduit for indoor applications. NM-B cable would need to be installed in duct or conduit if it were being used in the same application as MC cable.
A Romex® NM-B cable uses the following component materials:
- Insulation: PVC
- Jacket: Nylon
- Conductors: Annealed soft copper
- Ground: Bare copper
With the help of these materials, Romex® is rated for:
- Temperatures of up to 90℃ in dry locations.
- Ampacity limited to 60℃.
- 600 volts.
Romex® wires are indeed very useful. However, always bear in mind that they have a very sensitive nature. Harsh, outdoor conditions can quickly cause this cable to deteriorate. Making sure you comply first with the National Electric Code (NEC) before you set a wiring project in motion can save you lots of trouble.
Types of Romex® Wire
Romex® wire comes in several convenient sizes ranging from American Wire Gauge (AWG) 14 to 8. They’re also available with two or three conductors. We understand that you have exact lengths and want to limit waste, so we allow you to purchase any length at all on Romex® wire. Plus, we offer discounts on bulk purchases.
Romex® wire comes in different sizes depending on how much power needs to be run. The most popular sizes are the 14 AWG, 12 AWG and 10 AWG, and they are each specified with their own color. The Romex® 14/2 and 14/3 have a white jacket, the Romex® 12/2 and 12/3 have a yellow jacket and the Romex® 10/2 and 10/3 come in the orange jacket. Anything bigger than the 10 AWG Romex® comes in a gray outer jacket. To get different colors in these large cables, you’ll need to request a minimum run of 50,000 feet of wire.
The color codes make it much easier for an electrical contractor to tell the difference between cables just by looking at them. For instance, they might get a phone call from a residential customer who needs to replace a wire that was cut or ripped. They can just ask what color the wire is and ensure they bring the correct one for the job.
The color only represents the AWG size of the wires inside the jacket so that an electrician knows what size it is by looking at it. You should always speak to an electrician before trying to pick an AWG size yourself because there are many different factors to think about first. They will ask you the proper questions to get the information that they need and then run the calculation for the right AWG size.
Approvals and Dependability
To ensure appropriate use in its many different applications, Romex® wire complies with several different standards and specifications, including those from the National Fire Protection Agency (NFPA), ASTM International, the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH), and Restriction of Hazardous Substances (RoHS):
- UL Standard 719
- UL Standard 83
- ASTM B-3 and B-8
- Federal Specification A-A-59544
- NEC, NFPA 70
- REACH and RoHS
All Romex® wire is manufactured in the U.S. with a cost-efficient process that makes it great for basic indoor applications. This intended use means it must be built to certain standards. As long as the wire is made domestically, then you can be assured you’re getting the right product, especially since all Romex® wire comes from Southwire.
At WesBell, we buy all of our wire and cable from the largest most reliable manufactures in the industry, like Southwire, who require large stocking orders and year-end minimums. Not only does that mean we sell a quality product from the source, but we also have the cheapest price. The Southwire brand means you’re getting a product that came from the best in the business.
Tips for Working With Romex® NM-B Wire
Remember, Romex® wire isn’t the most rugged type of wire on the market. While it’s great for many indoor applications, you’ll still have to take some precautions. Here are a few of our tips for working with Romex® NM-B wiring:
- Take care with entry and exit points: Your first priority must be preventing damage to the Romex’s® sheathed cables at any point where it will enter or leave. You must make sure that these points are fitted by the appropriate connectors or brushings at all times. Look for connectors and brushings that are specifically manufactured for Romex® conduits.
- Select the right conduit sizes: You must also be careful not to place your Romex® wire in conduits that are too small for the cable size. Doing this may damage, bind or crush the sheathing. Make sure you always select a conduit size that will allow your Romex® cable to pass through easily.
- Always check your local jurisdiction codes: The NEC codes usually vary from state to state. Look for your local code enforcement building department so you can ask for guidance whenever you plan on installing Romex® wires. They will send a building inspector as well as an experienced technician to check if your wiring project can be approved.
- Watch your placement: Try to place your Romex® wires in PVC pipes before using them. Make sure the wires are not buried more than 3 to 4 inches from the ground’s surface. If you can, just run the wires along building boulders — you can, later on, clip them in place so that they won’t slip or be exposed to element exposure.
If you can, hire a good technician who can help you obtain stable electrical conditions, especially when the wires are installed outdoors. Make sure you replace your Romex® wires after a year or two, and always have your wires inspected so that they will still conform to NEC standards during use.
Romex® vs. Other Cables
Underground feeder (UF-B) cables are similar to Romex® wiring, but they offer more protection for outdoor and underground applications. This cable is only available in gray and does not need to be run through conduit, though you can choose to do so if you prefer. UF-B cable has the same inner wires as Romex® — it’s also made with THHN wires and a bare copper ground wire. However, with UF-B, the ground wire and the THHN wires are individually covered by the extra protection of the UF-B jacket.
All Romex®, or NM-B cables, must stay indoors. They cannot run outdoors at all because they don’t have enough protection to withstand outdoor conditions. You can pay slightly more for a UF-B cable that runs indoors, outdoors and directly underground without conduit. Each conductor is covered individually by the thick durable PVC jacket. UF-B is also known as an underground cable because it can be buried directly in the earth to hook up a new electrical panel in places like barns or garages.
If you don’t need multiple wires in one cable, you can opt for the thermoplastic high-heat nylon wire (THHN) or the thermoplastic high-heat water-resistant nylon (THWN) wires on their own. These are the wires that make up the conductors within Romex®. We also have hook-up wire for indoor use on appliances and welding cable for flexible outdoor use.
Moving from Romex®, the next step up for an outdoor cable is Type MC cable, which is also made with THHN wires and an additional green THHN wire as a ground. Having a THHN ground wire means the cable can be used outdoors or in conduit because there’s no chance of moisture hitting the bare copper. “MC” stands for metal-clad because the jacket is an aluminum metal-clad jacket, which is great for pushing MC cable through conduit.
We also offer many types of portable power cable that have rubber insulation and jacket for added flexibility and protection outdoors.
Romex® Wire From WesBell Electronics
Here at WesBell, we only sell high-quality Romex® wire from Southwire, so you can expect a long-lasting, cost-effective cable for many different indoor applications. If you’re not sure what you need, our expert technicians can help you find the right wire for your project.
In addition to top-of-the-line customer service, we offer wire processing services, so we can cut, strip and otherwise prepare cables for your application. Reach out to us today to learn more or for help selecting the best cable for your work. Or, if you know just what you need, take a look at our UF-B cables at the links above.