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numerous nm cables running into an electrical box

NM Cable

Originally contributed by Jeff Butler • last updated 1/14/2021

In most cases, the wiring inside our homes is done by professionals, requiring little knowledge or expertise on the part of the homeowner. However, if you’re looking to wire up a new light fixture or GFCI plug, there’s a good chance you’ll come across terms such as Romex brand or NM cable.

Definition

The term NM cable (non-metallic sheathed cable) refers to a type of electrical wire that is typically used in residential and light commercial electrical systems. NM cable is often incorrectly referred to by the brand name Romex, Romex wire, or 14/2 Romex (a trademarked brand of the Southwire Company) in the same way tissue paper is commonly called Kleenex. NM cable generally consists of two or three insulated copper conductor wires, an uninsulated ground wire, and a thick outer thermoplastic sheathing. With most modern NM cables, the color of the sheathing indicates the wire gauge, with one of the most common, 14 AWG wire, typically being white.

A Couple Things To Know About NM Cable

There are a few different types of NM cables that are used for different purposes around the house. Here are a few key tips to make sure you choose the right one:

  • NM cable is commonly described as two-wire or three-wire cable, depending on how many insulated conductor wires (not including the uninsulated ground wire) are inside the thermoplastic sheathing. For example, 14/2 wire has two 14 gauge conductors and one uninsulated ground wire inside the sheathing. Whereas, a 12/3 has three 12 gauge wires and one ground.
  • If you’re wiring up a connection outside, there is a special NM cable that’s designed to be buried underground known as underground feeder cable (UF-B). It’s what you’ll need if you want to run power to a shed or garage.
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