If you're planning electrical wiring in a home or small building, you've likely come across
NM-B Building Wire
. But what is it exactly—and where should it be used?
This guide will explain what NM-B cable is, what it’s used for, and why it's one of the most common types of residential wiring in the U.S.
What Is NM-B Wire?
NM-B stands for Non-Metallic sheathed cable, Type B. It is an indoor electrical cable used primarily for residential and light commercial wiring.
Key features of NM-B wire:
Non-metallic (NM) sheath: Flexible PVC jacket that's easy to pull through walls and ceilings.
Multiple conductors: Usually comes with 2 or 3 insulated copper wires, plus a bare ground wire.
Rated for 600 volts
Temperature rating: 90°C (194°F) dry conditions
Common trade names include Romex®, which is often used interchangeably with NM-B.
What Is NM-B Wire Used For?
NM-B cable is mainly used for indoor branch circuit wiring in dry, protected environments. It's ideal for powering:
✅ General Lighting Circuits
Standard ceiling lights and wall fixtures
Connected to 15A or 20A breakers using 14 or 12 AWG NM-B
✅ Electrical Outlets (Receptacles)
Standard wall outlets in bedrooms, living rooms, and other dry locations
✅ Switches and Fans
Light switches, ceiling fans, and wall-mounted devices
✅ Kitchen and Bathroom Circuits
NM-B is used in dry parts of these rooms—like outlets above counters
GFCI protection is added as required by code
✅ Appliance Circuits
Water heaters, dishwashers, and other hard-wired appliances (with appropriate wire gauge)
Typical Sizes and Their Applications
| NM-B Size | Amperage Rating | Common Use |
|---|---|---|
| 14/2 NM-B | 15 amps | Lighting circuits |
| 12/2 NM-B | 20 amps | General-purpose outlets |
| 10/2 NM-B | 30 amps | Water heaters, dryers (120V loads) |
| 10/3 NM-B | 30 amps | Electric dryers (240V) |
| 8/3 or 6/3 NM-B | 40–50 amps | Ranges, ovens, larger appliances |
Note: The first number is the wire gauge, and the second is the number of conductors (excluding ground).
Where Not to Use NM-B Wire
NM-B wire is not suitable for the following conditions:
Outdoor use (unless in conduit rated for outdoor exposure)
Wet or damp locations (e.g., underground, wet walls)
Exposed to direct mechanical damage
Inside conduit underground (Use UF-B or THWN-2 instead)
Always follow NEC (National Electrical Code) and local building codes.
Why Electricians Like NM-B Cable
Lightweight and flexible – easy to pull through studs and joists
Cost-effective – cheaper than metal-clad or conduit wiring
Code-approved – widely accepted for residential construction
Safe – with built-in ground conductor and insulation rated for dry environments
Conclusion
So, what is NM-B wire used for?
It’s the go-to wiring solution for indoor residential circuits—including lighting, outlets, switches, and many appliances. Safe, affordable, and easy to install, NM-B wire is a trusted standard in modern electrical systems.
Need Help Choosing the Right NM-B Wire?
We supply NM-B copper cables in all popular gauges (14 to 6 AWG) for residential and light commercial applications. Contact us today for expert advice and competitive pricing.
