What exactly is Romex?

Romex is a brand name, owned by Southwire, for NM-B nonmetallic sheathed cable. Inside the plastic jacket sit insulated hot and neutral conductors plus a bare ground, ready to staple to studs.

It became the default for US homes because it needs no conduit, pulls fast, and costs little. The jacket colors follow gauge by convention: white for 14, yellow for 12, orange for 10.

Its territory is dry, enclosed residential spaces. Wet locations, underground runs, and most commercial buildings are off limits, and a few cities like Chicago ban it in favor of conduit.

Older NM from before 1984 has a lower temperature rating, and pre-1960s versions may lack a ground entirely.

Matching cable type to circuit is half the job; the electrical wire size tool handles the other half.