In the North American electrical industry, commonly used residential and light commercial wires include NM-B, THHN, UF-B, and XHHW.
When purchasing or installing wiring, many people often encounter the same question: "Is NM-B the same as Romex?"
This article will provide a detailed explanation from the perspectives of definition, applications, standards, and wire selection. By the end, you will have a clear understanding of the relationship between NM-B and Romex, along with practical guidance for choosing the right type of wire for your project.
Definition: NM-B vs. Romex
What is NM-B?
- NM-B (Non-Metallic Sheathed Cable, Type B) is a type of cable commonly used in residential and light commercial buildings.
- It consists of multiple insulated conductors plus a bare ground wire, all covered with a non-metallic sheath.
- It complies with UL 83 and UL 719 standards and is intended for dry, indoor fixed wiring.
What is Romex?
- Romex is not a wire type but rather a brand name owned by Southwire Company in the United States.
- The Romex brand mainly manufactures NM-B cables, which is why many people use "Romex" and "NM-B" interchangeably.
The Relationship Between NM-B and Romex
- Put simply: NM-B is a wire type, Romex is a brand.
- Romex-manufactured NM-B cables are among the most widely recognized NM-B cables in the market.
Main Applications of NM-B Cable
NM-B cable is widely used in residential and light commercial indoor wiring. Here are some typical applications:
| Application | Recommended Type | Purpose | Example Loads |
|---|---|---|---|
| General lighting & outlets | 14/2 NM-B | For 15A circuits | Light fixtures, general outlets |
| Kitchens & bathrooms | 12/2 NM-B | For 20A circuits | Kitchen appliances, hair dryers |
| Dryers & small A/C units | 10/2 NM-B | For 30A circuits | Electric dryer, small A/C |
| Electric ranges & water heaters | 8/2 NM-B | For 40–50A circuits | Range, water heater |
| Large appliances & subpanels | 6/3 NM-B | For 55A circuits | Hot tubs, subpanels |
Key Point: NM-B is ideal for indoor fixed wiring, but it should not be used for direct burial or outdoor exposure.
NM-B vs. Other Common Wire Types
To help customers better understand where NM-B fits in, here's a comparison with other common UL-approved wire types:
| Wire Type | Suitable Environment | Features | Typical Applications |
|---|---|---|---|
| NM-B | Indoor dry locations | Lightweight, easy to install, non-metallic sheath | Residential lighting & outlets |
| UF-B | Outdoor & direct burial | Thicker sheath, moisture & UV resistant | Garden lights, outdoor receptacles |
| THHN/THWN | Conduit installations | Single conductors, heat & moisture resistant | Industrial wiring, commercial buildings |
| XHHW | Damp/high-temperature areas | XLPE insulation, strong weather resistance | Transformers, heavy-duty equipment |
How to Choose the Right Wire?
When selecting electrical wires, electricians and procurement specialists should consider the following factors:
By Installation Environment
- Indoor dry locations → NM-B
- Outdoor or underground → UF-B
- Industrial or conduit installations → THHN / XHHW
By Circuit Load
- General lighting → 14 AWG
- Kitchen/Bathroom outlets → 12 AWG
- Heavy appliances → 10 AWG – 6 AWG
By Safety Certification
- Always choose products with UL & cUL certifications to ensure compliance with North American safety standards.
Frequently Asked Questions
Q1: Is NM-B the same as Romex?
- No. Romex is a brand, NM-B is a wire type. Many people call Romex NM-B simply "Romex" out of habit.
Q2: Can NM-B be used outdoors?
- No. NM-B is designed only for dry, indoor use. For outdoor or direct burial, use UF-B or THHN/XHHW.
Q3: What are the common sizes of NM-B?
- Standard sizes include 14/2, 12/2, 10/2, 8/2, 6/3, covering 15A to 55A applications.
Through the above analysis, we can clearly see that NM-B and Romex are not identical: NM-B is the wire type, while Romex is one of the most recognized brands producing NM-B cable. NM-B is mainly suited for indoor dry environments, while other types such as UF-B, THHN, and XHHW are recommended for outdoor or industrial use.
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Tel/WhatsApp/Wechat: +86 135 1078 4550 / +86 136 6257 9592
Email: manager01@greaterwire.com
No matter the scale of your project, we are ready to provide you with professional technical support and enthusiastic service, ensuring you receive the most suitable cable solutions.