Types of Cable: NM, MC, and UF

NM cable, the residential standard

Nonmetallic-sheathed cable, NM, the kind everyone calls Romex, is the backbone of house wiring. It has insulated conductors and a bare ground wrapped in a plastic jacket. It is cheap, fast to run, and easy to work with.

The catch is where it can live. NM is for dry, protected indoor locations. It cannot be used outdoors, buried, in wet areas, or left exposed where it could get damaged. Keep it inside the walls where it belongs.

MC cable, the commercial cousin

Metal-clad cable, MC, wraps the conductors in a flexible metal armor. That armor protects the wires physically and makes MC common in commercial buildings and exposed locations where NM is not allowed. It runs fast like NM but takes more abuse.

Cut the armor cleanly, use an anti-short bushing at every termination, and support it correctly. That little red bushing is a classic inspection item people forget.

UF cable for the wet and buried

Underground feeder cable, UF, looks like NM but the conductors are molded into a solid, moisture-resistant jacket. That lets it be direct-buried and used in wet locations, which is exactly what NM cannot do. Use it to feed a detached garage, a well pump, or outdoor lighting.

• Direct burial at the required depth, or in conduit for extra protection.
• Wet and damp locations where NM is prohibited.
• Protect the portion that emerges from the ground in conduit.

Choosing correctly keeps you compliant

The fastest way to fail an inspection is using the wrong cable for the environment: NM in a damp basement, or exposed where it gets bumped. Match the cable to the location and you have solved most of the problem before you cut a single foot.

When in doubt, ask what the location is: dry and protected, exposed, wet, or buried. That one question points you straight to NM, MC, or UF nearly every time.