When choosing electrical wire for your project, one of the most common questions is: Is NM-B wire fire resistant?
For overseas buyers who may not be familiar with NM-B wire, this article provides a complete guide: from the basics of NM-B wire, fire resistance performance, common customer FAQs, to a comparison with other products.
With this knowledge, you'll be able to select the right wire with confidence for your residential, commercial, or industrial project.
What is NM-B Wire?
NM-B (Non-Metallic Sheathed Cable, Type B) is one of the most widely used electrical cables in the U.S. for indoor residential wiring. It consists of:
- Copper conductors (solid or stranded)
- PVC insulation for each conductor
- PVC outer jacket (color-coded for size identification)
The "B" in NM-B indicates that the wire is rated for 90°C dry locations.
Is NM-B Wire Fire Resistant?
NM-B wire is designed for indoor, dry environments. Its PVC jacket meets basic UL flame-retardant requirements, but it is not a fire-resistant cable.
In case of fire, the insulation will melt and cannot maintain circuit integrity.
That means:
- NM-B = safe for normal residential use
- But not suitable for fire-critical circuits (emergency lighting, fire pumps, tunnel wiring, etc.)
Fire Resistance Comparison Table
| Wire Type | Fire Resistance | Applications | Notes |
|---|---|---|---|
| NM-B | ❌ Not fire resistant (only basic UL flame test) | Indoor, dry locations | Cost-effective, but not for fire-rated circuits |
| UF-B | ❌ Not fire resistant (but thicker jacket) | Underground, damp locations | Moisture resistant, not fire resistant |
| THHN/THWN | ✔ Flame-retardant in some models | Indoor conduit, some outdoor use | Higher heat & flame rating than NM-B |
| XHHW | ✔ Flame-retardant, heat resistant | Indoor/outdoor, industrial use | XLPE insulation, better fire performance |
| Fire-Resistant Cable | ✅ Fully fire resistant | Emergency, tunnels, fire circuits | Maintains power supply 90–120 minutes under fire |
👉 Key takeaway: If you need fire resistance, choose XHHW or fire-resistant cables-not NM-B.
Common Customer Questions and Answers
(1) Basic Understanding
- What is NM-B wire used for?
→ Mainly for indoor residential wiring, such as lighting and outlets.
- What's the difference between NM-B and THHN, UF-B, Romex?
→ NM-B = indoor only; THHN = conduit wiring; UF-B = underground; Romex = brand name of NM-B.
- What does the "B" stand for?
→ Rated for 90°C dry conditions.
(2) Specifications
- What sizes are available?
→ 14/2, 12/2, 10/3, etc. (from 14 AWG to 6 AWG).
- Conductor material?
→ 100% copper.
- Jacket colors?
→ Yellow = 12 AWG, White = 14 AWG, Orange = 10 AWG (for easy ID).
- Solid or stranded?
→ Mostly solid for NM-B. Stranded available on request.
- Ampacity?
→ 14 AWG = 15A, 12 AWG = 20A, 10 AWG = 30A.
(3) Usage & Performance
- Can NM-B be used outdoors or buried?
→ No. Indoor dry use only.
- Waterproof or UV resistant?
→ No. For wet/outdoor, choose UF-B or THWN.
- Can NM-B be installed in conduit?
→ Yes, but not required indoors.
- Voltage rating?
→ 600V.
(4) Certification & Standards
- Is your NM-B UL certified?
→ Yes, UL & cUL listed, compliant with NEC.
(5) Procurement & Service
- MOQ? → Flexible, supports small and bulk orders.
- Packaging? → Coils, reels, or cartons.
- Delivery time? → Fast lead time, export-ready.
- Customization? → Yes-color, length, label, packaging.
- Payment terms? → Multiple international methods.
- Samples? → Free samples available.
(6) Price & Cooperation
- How much does NM-B cost?
→ Price depends on size and order quantity.
- Bulk discounts?
→ Yes, competitive wholesale pricing.
- Shipping?
→ Support FOB, CIF, door-to-door international logistics.
- Why choose you?
→ ✔ Complete range (NM-B, THHN, UF-B, XHHW)
→ ✔ UL & cUL certified, U.S./Canada compliant
→ ✔ Full sizes: 14 AWG–6 AWG
→ ✔ Strong supply chain, fast delivery
→ ✔ Professional technical support, global partners
Choosing the Right Wire
| Project Type | Recommended Wire | Reason |
|---|---|---|
| Indoor residential wiring | NM-B | Cost-effective, UL listed |
| Underground outdoor wiring | UF-B | Moisture-resistant, direct burial |
| Conduit wiring (indoor/outdoor) | THHN/THWN | Higher temperature & flame rating |
| Industrial & high-temp | XHHW | Flame-retardant, heat resistant |
| Fire emergency systems | Fire-Resistant Cable | Maintains operation under fire |
Work with Us
No matter the size of your project-small residential jobs or large-scale commercial installations-our team provides professional technical support, high-quality products, and fast global service.
Dongguan Greater Wire & Cable Co., Ltd.
📞 Tel/WhatsApp/Wechat: +86 135 1078 4550 / +86 136 6257 9592
📧 Email: manager01@greaterwire.com