Nonmetallic-Sheathed Cable (NM)

Article 334 limits NM cable to specific occupancies, requires securing within 12 in of boxes and every 4.5 ft, and derates its conductors to the 60 °C column.

When it applies

NM cable, what everyone calls Romex, is the workhorse of dry, indoor residential wiring. You will run it inside stud bays and above ceilings in most homes. What it is not built for is exposure to moisture, direct sunlight, or spots where it can get knocked around, so it stays inside the protected structure of the building.

Common mistakes

• Leaving cable unsupported. It needs securing within a set distance of each box and at regular intervals along its run.
• Running it exposed on a basement wall or garage where it can be damaged, instead of protecting it with conduit or running it through framing members.
• Overfilling a box because nobody counted the conductors.

In the field

When I fish NM through an unfinished basement, I keep it stapled neatly up along the joists and never let it dangle where a stored ladder or bike could rub through the jacket over time.