Electricity completely revolutionized the way we built our homes. Architects and engineers have had to adapt to new inventions over the last hundred years, from lamps and fans to HVAC units and appliances. But, all these appliances are worthless without the wiring to convey the electricity safely. Think of a house as a human body; the electricity is the blood, and the wires are the veins.

Much like the appliances and technology in our home, wiring has dramatically changed since its early stages. Today, there is a wide variety of wiring you might discover if you look around a little. If you have an old home, you may likely find a couple of different types of wiring or an abandoned system.

Here is a look at the different types of wiring used in homes.

NM Non-Metallic Cable

Identifier: The NM non-metallic cable is a plastic jacket that can come in various colors depending on the gauge of the wire. It is usually installed by stapling the wire to floor joists, wall studs, and ceiling rafters in unfinished spaces.

Non-metallic (NM) electrical cable is commonly known by the brand name Romex. The name is said to come from the company’s roots in Rome, New York. It was the first company to produce the product, and it is still the most common brand name on the market.

This wiring contains three wires protected by wire insulation and a plastic jacket. The wires are individually wrapped in plastic insulation with color coding. The black wire is the “hot” wire, white is neutral, and green is the ground. Around these wires, you may find paper creating a barrier between the insulation and the jacket.

The jacket is made from 30-mil thick PVC and is also color-coded to indicate the gauge of the wire. Wire gauges are important because they indicate the size of the wire, which in turn, indicates how much electricity the wire can convey safely. The jacket is easy to cut through with a knife or electrician’s tool for splicing or capping.

Non-metallic wiring is the most common type of wiring in the United States. This is most likely because it is affordable, lightweight, and easy to use. NM wiring easily bends to slide through holes in wall studs. It is easy to install with cable staples, and it is cheaper than its modern counterpart, metal-sheathed wiring. Non-metallic cable is especially prominent in the southern half of the country, where temperatures stay milder.

Metallic Sheathed Cable

Identifier: The metallic-sheathed cable has a metal covering around the wires that run through metal junction boxes. These cables are usually found on the walls of finished and unfinished spaces, especially in commercial properties.

Metallic-sheathed cable has many names like Type AC, MC, Greenfield, Armored Cable, and BX Cable. That’s because it is one of the oldest types of wiring in both commercial and residential construction.

Metallic-sheathed cable is easy to identify because it is armored. A relatively thick metal coil protects the wires inside from being cut, nicked, or spliced. The coil also provides the ground for the wiring system, so the third green coated wire is not necessary. However, the junction boxes and electric panels must be grounded in a system like this.

Although metallic-sheathed cable has become less popular than non-metallic cable, there are still many uses for it today. Metallic-sheathed cable is rated for outdoor use, while NM is not. This is not only due to the extra protection of the metal but also the protection from the elements. Metallic-sheathed cable is more prominent in colder climates because NM cable is more prone to freezing and cracking.

Non-Metallic Vs. Metallic Sheathed

As the two most prominent wiring systems in the country, non-metallic cable and metallic-sheathed cable have their pros and cons. While some regions of the country have a climate that requires metallic-sheathed cable, warmer climates typically use non-metallic cable. However, different circumstances call for different materials. Even in a warm climate, you cannot run non-metallic cable outdoors.

Non-Metallic Pros

  • Much more affordable than metallic-sheathed cable
  • Much easier to find in stores
  • Easy for anyone to install
  • Provides a ground wire for safety

Non-Metallic Cons

  • Susceptible to damage from nails and other building materials
  • Not rated for outdoor use
  • Not as safe as metallic-sheathed cable in cold climates

Metallic Sheathed Pros

  • Exceptionally durable
  • Safe for use outdoors and in cold climates
  • Metal sheathing provides the ground

Metallic Sheathed Cons

  • More expensive than NM cable
  • Heavier and harder to install
  • Requires a special tool or hacksaw to cut
  • Must be run through metal boxes with proper grounding

Knob and Tube

Identifier: Ceramic knobs on the joists and rafters of your home are the most common sign that knob and tube wiring is present or once was. The wire insulation in this system is a woven cloth that wraps around the wires.

These are the oldest type found in homes, and most were present before the 1950s. This system consisted of two single wires, one hot and one neutral, throughout the house’s framing. Electricians installed ceramic insulators to keep the wires from touching each other or other combustible materials, like the wood your house is framed with.

The wire insulation is usually very hard to decipher neutral from hot because they are old and dirty. Some neutral lines had white insulation. Some were black, however, like the “hot” line that comes with a white line. There is no ground in a knob and tube wiring system. The ground is a safety wire in modern systems that helps prevent fire and shock. Safety features that require a ground include GFCI outlets and surge protectors.

Knob and tube wiring becomes very hazardous when the insulation wears away or is covered in building insulation. Both situations present a serious fire hazard in your home. Knob and tube wiring is also too old to handle most modern appliances. Anything larger than 20 amps, like a modern kitchen appliance, also poses a serious fire and shock hazard.

Now that you have a general understanding of the most common types of wiring found in a home, you can venture through your unfinished attic and basement and see what you find. Make sure to check for any damage to your wiring, whether that be a staple that has cut through the jacket on a line of Romex or a metallic-sheathed cable that passes through an ungrounded box. If you find knob and tube wiring in your home, call a professional electrician.

Our Services

Our highly skilled electricians at Arc Angel Electric are a fantastic resource for diagnosing the condition of your home’s wiring. Whether you’re contemplating an upgrade, worried about potential damage, or want to add new lines to your home, we have you covered. Call us today for high-quality service and professional customer service. We serve residents in Cumming and Greensboro, GA, as well as residents in Mount Pleasant, SC. We offer surge protection, electrical services, generators, EV charging, indoor lighting, and more.