What Is NM-B Wire Used For? | A Practical Guide

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

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.