Navigating the world of electrical cables can sometimes feel like decoding an alphabet soup of acronyms. Two terms that often cause confusion are Romex and NM-B. Are they the same thing? Is one better than the other? This guide will demystify these common types of residential wiring, explaining their relationship, key features, and how to select the perfect cable for your next installation.
What is Romex Wire?
Let’s start with a clarification: “Romex” is a brand name. It is not a generic type of cable. Romex is the trademarked name for a popular line of non-metallic sheathed electrical cable manufactured by Southwire, one of North America’s largest wire producers. Due to its longstanding prevalence in the market, the term “Romex” has become a common genericized trademark—much like “Kleenex” for tissues—used by many electricians, contractors, and DIYers to refer to any NM (Non-Metallic) cable.
A standard Romex cable consists of two or more insulated THHN (Thermoplastic High Heat-resistant Nylon-coated) conductors and one bare ground wire, all bundled together and encased in a flexible plastic jacket.
What is NM-B Wire?
NM-B is the official, generic classification for this type of cable. The “NM” stands for Non-Metallic, indicating its outer sheath is not made of metal. The “-B” suffix is crucial—it denotes the temperature rating of the insulation. NM-B wire is rated for 90°C (194°F), but its ampacity (current-carrying capacity) is typically based on the 60°C column in the National Electrical Code (NEC) for residential use, as that is the rating of the terminations (breakers, outlets) in most dwellings.
Therefore, NM-B is the correct, all-encompassing technical term for the flat, sheathed cable you find at hardware stores, commonly (and often incorrectly) called “Romex.”
The Commonalities Between Romex and NM-B Wire
In everyday practice, when people say “Romex,” they are almost always referring to NM-B cable. Here’s what they share:
- Application: Both are designed for dry, indoor locations in residential construction. This includes running wires inside walls, ceilings, and floors for outlets, switches, and lighting.
- Construction: They feature the same basic design: individually insulated conductors (usually copper) and a bare copper ground wire wrapped in a non-metallic, flame-retardant plastic jacket.
- Code Compliance: Legitimate Romex brand cable and other manufacturers’ NM-B cables must meet the same stringent safety standards outlined in the NEC and be UL-listed or certified by other recognized testing laboratories.
- Conductor Types: The insulated wires inside are typically THHN, which provides good heat resistance and durability.
Key Differences Between Romex and NM-B Wire
The primary difference is specificity versus generality. Think of it like this: all Romex-brand cables are a type of NM-B wire, but not all NM-B wires are “Romex.”
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Feature
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Romex™ Wire
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NM-B Wire
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Definition
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A brand name for NM-B cable manufactured by Southwire.
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The generic product category and technical designation for non-metallic sheathed cable.
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Relationship
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A specific subset of NM-B wire.
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The umbrella term that includes Romex and all other equivalent brands.
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Origin
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Proprietary to Southwire Company.
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A standardized type manufactured by many companies (including JZD Cable).
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Identification
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Will be clearly marked as “Romex” on the cable jacket.
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Will be marked with “NM-B” and the manufacturer’s information.
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Variations
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Sold under the Romex brand name (e.g., Romex SIMpull).
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Available from numerous brands, each with potential slight variations in jacket material, flexibility, or color.
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Choosing the Right Cable for Your Project
- Understand the Terminology: When shopping or discussing a project, know that “NM-B” is the correct technical term. If someone says “Romex,” they most likely need standard NM-B cable.
- Check Local Codes: Always verify that NM-B cable is approved for your specific application in your local jurisdiction, as codes can vary.
- Read the Jacket: Don’t just ask for “Romex.” Look at the cable jacket printing. It should clearly state “Type NM-B” along with the gauge (e.g., 12/2 WG or 14/3 WG), a voltage rating (e.g., 600V), and listing marks (like UL).
- Choose a Reputable Brand: While the function is identical, the quality of materials and manufacturing can differ. Opt for cable from a trusted manufacturer that guarantees consistency, durability, and full compliance with safety standards.
Power Your Projects with Confidence from JZD Cable
Whether you call it Romex or NM-B, selecting high-quality, reliable non-metallic sheathed cable is non-negotiable for safety and performance. At JZD Cable, we specialize in manufacturing premium electrical wires and cables that meet and exceed international standards.
Our NM-B cables are engineered for:
- Superior Safety: Featuring flame-retardant jackets and high-grade copper conductors.
- Easy Installation: Designed with flexibility and stripability in mind for efficient work.
- Uncompromising Quality: Rigorously tested to ensure compliance and long-term reliability.
Don’t settle for uncertainty in your wiring supplies. Choose a partner committed to clarity and quality.
Contact JZD Cable today to learn more about our full range of NM-B cables and other electrical wiring solutions.
