If you are thinking of running wiring in your home, you will have several options of the type of wire to use and how to protect it; however, two of the most popular choices are NM cable and armored cable. Both types of cable are very popular with DIYers because they are easy to work with and can be used in many applications without the need for metal conduit (if allowed by the building code and inspectors).
NM cable stands for nonmetallic cable and is a fully self-contained electrical wiring product. The cable often has three wires (positive, neutral, and ground) inside a hard plastic or rubber sheathing. It is relatively inexpensive and is extremely easy to work with. Although it is sometimes installed inside conduit, most people choose NM cable because of its flexible self-contained sheathing. Generally speaking, NM cable is usually passed through studs and walls without any additional protective covering and is fine for many types of residential applications.
NM cable (which is also commonly referred to as Romex) is primarily used to wire new switches and outlets in a home or during a remodeling project. It has been used seldom in new home construction; however, there are indications that more and more contractors are using NM cable in the few cities and municipalities where it is allowed by building inspectors. This is because of its relatively low price when compared to wiring that is encased in metal conduit. Installation of NM or Romex cable is also much faster than working with conduit and individual wires.
Areas that limit the use of NM cable do so for some very compelling reasons. Although newer types of NM cable have displayed an ability to be more resistant to heat and damage, many brands of the cable are still susceptible to damage from high temperatures or being nicked during installation. In the event of a fire, NM cable burns and disintegrates very quickly, which could lead to electrical arcing or sparking that could create a potentially even deadlier fire hazard.
Like NM cable, the armored cable is also a self-contained, flexible electrical wiring solution. However, the armored cable is encased in a flexible metal type of sheathing. Because it is encased in metal, the armored cable is considered to be more durable and damage resistant than NM or Romex cable. However, the armored cable is slightly harder to work with and may require specialized tools in some applications. While many people choose to cut armored cable with a hack saw, this is been shown not to be the best way to cut the cable. Cutting armored cable with a hack saw has been known to lead to nicks in the wiring which could cause a potential fire hazard. Armored cable is also considerably more expensive than an NM cable.
On the other hand, many cities and municipalities now allow all for the use of armored cable in most commercial and residential applications. While NM cable can be used in some residential remodeling projects, armored cable is now accepted in almost all types of construction by city planning offices and local building inspectors.