In electrical engineering and building wiring, the safety and durability of wires are critical. For both indoor and outdoor applications-especially when exposed to direct sunlight-the UV resistance of a cable determines its service life and reliability.
When choosing NM-B wire (Non-Metallic Sheathed Cable, Type NM-B), many customers often ask a key question: Is NM-B wire UV resistant?
This article will address that question by analyzing the technical features, application limits, and suitability compared with other wire types. We will also provide real-life usage cases and selection guidelines, including a comparison table to help customers make the right purchasing decision.
What Is NM-B Wire?
NM-B wire is one of the most widely used building cables in the U.S. and Canadian markets, commonly applied in residential and commercial fixed wiring. Its main structure includes:
- Conductor: Solid or stranded copper (standard sizes 14 AWG – 6 AWG) with excellent conductivity;
- Insulation: Thermoplastic PVC with a temperature rating up to 90°C;
- Sheath: Non-metallic PVC jacket, available in colors such as yellow, white, and orange for easy identification of sizes;
- Application: Primarily used for indoor dry environments, such as receptacles, lighting circuits, and branch wiring between the panel and end-use devices.
👉 Key point: NM-B wire is designed for indoor dry environments and is not intended for outdoor or direct sunlight exposure.
Can NM-B Wire Be Installed Outdoors?
Many users wonder whether NM-B wire can be installed outdoors. The answer is: Not recommended.
- Reason 1: NM-B does not have moisture or UV resistance. Prolonged exposure to outdoor conditions will cause the PVC jacket to deteriorate and crack.
- Reason 2: Rain, snow, humidity, and high temperatures significantly shorten cable lifespan and increase the risks of shock or fire.
- Best practice: For outdoor wiring, use UF-B, THHN, or XHHW cables, or install NM-B inside a protective conduit.
Is NM-B Wire UV Resistant?
The PVC jacket of NM-B wire has limited abrasion and aging resistance indoors, but it does not provide long-term UV protection. This means:
- When exposed to sunlight for extended periods, the jacket will degrade, become brittle, and crack;
- Once the jacket is compromised, the insulation may be exposed, creating risks of short circuits, electrical leakage, or even fire;
- Therefore, NM-B wire is not suitable for outdoor, rooftop, or sun-exposed applications.
👉 Conclusion: NM-B wire is not UV resistant and should not be used in outdoor environments with direct sunlight.
Do Different Jacket Colors Have Different UV Resistance?
NM-B wire is manufactured with outer PVC jackets in different colors-commonly white, yellow, orange, and sometimes black. These colors, however, do not indicate UV resistance. Instead, they serve the following purposes:
- White jacket: Typically used for 14 AWG NM-B wire.
- Yellow jacket: Typically used for 12 AWG NM-B wire.
- Orange jacket: Typically used for 10 AWG NM-B wire.
- Black or gray jacket: Occasionally used for larger gauges.
👉 Key insight: The jacket color is a coding system for wire gauge and identification, not a measure of UV resistance. All NM-B jackets, regardless of color, are made from standard PVC and therefore share the same lack of UV resistance.
If UV resistance is required, switching to cable types specifically designed for outdoor use-such as UF-B, THHN, or XHHW-is the correct solution.
What If It Must Be Used Outdoors?
Although NM-B wire itself is not UV resistant, there are safe alternatives and protective measures:
1.Protective conduit installation: Run NM-B wire inside PVC or metal conduit when installed outdoors to avoid direct UV exposure.
2.Use alternative cable types: For outdoor or moisture-prone applications, choose wires designed with UV protection:
- UF-B Cable (Underground Feeder): Specifically designed for direct burial and outdoor use, with UV resistance.
- THHN/THWN Wire: Provides both moisture and UV resistance, widely used in outdoor and industrial settings.
- XHHW Wire: Cross-linked polyethylene insulation, highly resistant to heat, moisture, and UV radiation.
NM-B vs. Other Cable Types (UV Resistance & Applications)
| Cable Type | UV Resistant | Application | Features |
|---|---|---|---|
| NM-B | ❌ No | Indoor dry environments | Common for residential wiring; cost-effective, easy to install |
| UF-B | ✅ Yes | Outdoor, direct burial, wet areas | UV resistant, waterproof, safe for direct exposure |
| THHN/THWN | ✅ Yes | Outdoor, conduit, industrial wiring | Heat resistant, UV resistant, widely used in commercial projects |
| XHHW | ✅ Yes | Outdoor, industrial, solar systems | Excellent heat and UV resistance, long service life |
👉 From the comparison, NM-B is best suited for indoor use, while UF-B, THHN, or XHHW should be chosen for outdoor applications.
Real-World Applications
- Case 1: Residential Wiring
In U.S. homes, NM-B wire (14/2, 12/2, etc.) is widely used for outlets and lighting circuits, perfectly meeting indoor safety requirements.
- Case 2: Outdoor Garden Lighting
Using NM-B outdoors directly may lead to jacket damage in just a few years due to UV exposure. The correct choice is UF-B cable or placing NM-B in protective conduit.
- Case 3: Solar Energy Systems
Outdoor solar systems require long-term UV exposure resistance. XHHW wire is the right choice, preventing UV damage and ensuring safety.
Choose Greater Wire & Cable
When selecting wires, product quality and supplier reliability matter as much as specifications. Dongguan Greater Wire & Cable Co., Ltd. offers:
- Product Range: Complete line of UL-listed cables, including NM-B, THHN, UF-B, XHHW, covering all major applications;
- Certified Quality: UL & cUL certifications, fully compliant with U.S. and Canadian market standards;
- Full Specifications: Standard sizes from 14 AWG – 6 AWG, ideal for both residential and commercial projects;
- Fast Delivery: Capable of handling small or large volume orders with quick turnaround;
- Service Support: Professional technical guidance plus worry-free pre- and after-sales service;
- Global Experience: Years of manufacturing and exporting experience, trusted by partners worldwide.
👉 No matter the scale of your project, we provide expert guidance and dedicated service to ensure success.
Contact Us for More Information
NM-B wire is not UV resistant and is suitable only for indoor dry environments. For outdoor or sun-exposed applications, the right choice is UF-B, THHN, or XHHW cable. Choosing the proper wire type-and a reliable supplier-directly affects both safety and cost efficiency in your project.
We are committed to delivering high-quality wire products and professional technical support. For quotes, technical advice, or partnership inquiries, feel free to contact us anytime.
📞 Dongguan Greater Wire & Cable Co., Ltd.
Tel/WhatsApp/Wechat: +86 135 1078 4550 / +86 136 6257 9592
Email: manager01@greaterwire.com