What does 'NM' indicate in terms of outer layer?

The term 'NM' refers to Nonmetallic Sheath, which is a type of cable commonly used in residential wiring. This designation indicates that the outer layer of the cable is made from nonmetallic materials, providing insulation and protection without the added weight and cost of metal sheathing. Nonmetallic sheathing is advantageous in many applications, as it helps prevent moisture intrusion, reduces overall cable weight, and increases flexibility during installation.

This type of sheathing is typically used in methods like standard household electrical wiring, where the nonmetallic properties suffice to protect the wire from environmental factors typically experienced indoors. Other terms presented, such as Neutral Metal, New Material, and Non-moisture proof, do not accurately describe the characteristics or purpose of NM sheathing, which is specifically noted for its nonmetallic composition.