Electrical wire is typically made of copper or aluminum, and these conductive materials are insulated as wires that bring electricity to various parts of your home.
When you're installing new wiring, choosing the right wire or cable is half the battle. On the other hand, when examining the old wiring in your home, identifying the wire type can tell you a lot about the circuit the wiring belongs to (for example, if you open a junction box and need to determine which wires go where). Wiring for modern homes is quite standard, and most homes built after the mid-1960s have similar types of wiring. Any new electrical installation requires new wiring that conforms to local building codes.
Below, learn the different types of home electrical wires to choose the right option for completing electrical projects accurately and safely.
It helps to understand a few basic terms used to describe wiring. An electrical wire is a type of conductor, which is a material that conducts electricity. In the case of household wiring, the conductor itself is usually copper or aluminum (or copper-sheathed aluminum) and is either a solid metal conductor or stranded wire.
Most wires in a home are insulated, meaning they are wrapped in a nonconductive plastic coating. One notable exception is ground wires, which are typically solid copper and are either insulated with green sheathing or uninsulated (bare).
Many larger wires in your home are carrying 120- to 240-volt circuit voltage, often referred to as line voltage, and they can be very dangerous to touch. There are also several wires in your home that carry much lesser amounts of "low-voltage" current. These are less dangerous, and with some, the voltage carried is so low that there is virtually no chance of shock. However, until you know exactly what kind of wires you are dealing with, it's best to treat them all as dangerous.
01 of 06
- Best for: Interior use in dry locations
Often called “Romex” after one popular brand name, nonmetallic (NM) cable is a type of circuit wiring designed for interior use in dry locations. NM is the most common type of wiring in modern homes. It consists of two or more individual wires wrapped inside a protective plastic sheathing. NM cable usually contains one or more “hot” (current-carrying) wires, a neutral wire, and a ground wire.
These conductors are insulated in white (usually neutral) and black (usually hot) for installation. Most NM cables have a flattened tubular shape and run invisibly through the walls, ceiling, and floor cavities of your home.
Almost all of the wiring in outlets and light fixtures in a modern home is NM cable. This type of wire is used for hidden applications in the walls, as it is cheaper than using a conduit. The most common sizes and their amperage (amp) ratings are:
- 14-gauge (15-amp circuits)
- 12-gauge (20-amp circuits)
- 10-gauge (30-amp circuits)
- 8-gauge (40-amp circuits)
- 6-gauge (55-amp circuits)
NM cable is now sold with a color-coded outer jacket to indicate its wire gauge:
- White sheathing indicates NM cable with 14-gauge conductors.
- Yellow sheathing indicates NM cable with 12-gauge conductors.
- Orange sheathing indicates NM cable with 10-gauge conductors.
- Black-sheathed cable is used for both 6- and 8-gauge wire.
- Gray sheathing is not used for NM cable but is reserved for underground (UF) cable or service entrance cable (SE or SER).
NM cable is dangerous to handle while the circuit conductors are carrying voltage.
02 of 06
- Best for: Underground wire for outdoor fixtures
Underground Feeder (UF) is a type of nonmetallic cable designed for wet locations and direct burial in the ground. It is commonly used for supplying outdoor fixtures, such as lampposts. Like standard NM cable, UF contains insulated hot and neutral wires, plus a bare copper ground wire. But while sheathing on NM cable is a separate plastic wrap, UF cable sheathing is solid plastic that surrounds each wire. This type of electrical wire is also a bit more expensive than NM wire because of its durable insulation. UF cable is normally sold with gray outer sheathing.
UF cable is also used for major circuit wiring, and it carries a dangerous amount of voltage as long as the circuits are turned on.
03 of 06
- Best for: Insulated wire inside conduits
THHN and THWN are codes for the two most common types of insulated wire used inside conduit. Unlike NM cable, in which two or more individually insulated conductors (copper or aluminum) are bundled inside a plastic sheathing, THHN and THWN wires are single conductors, each with its color-coded insulation. Instead of being protected by NM cable sheathing, these wires are protected by tubular metal or plastic conduit.
Conduit is often used in unfinished areas, such as basements and garages, and for short exposed runs inside the home, such as wiring connections for garbage disposers and hot water heaters. These wires typically have similar prices to NM wire (plus the cost of the conduit). The letters indicate specific properties of the wire insulation:
- T: Thermoplastic
- H: Heat-resistant; HH means highly heat-resistant
- W: Rated for wet locations
- N: Nylon-coated, for added protection
THHN and THWN wires have colored sheathings that are generally used to identify their function in a circuit:
- Hot wires: Black, red, orange
- Neutral wires: White, brown
- Ground wires: Green, yellow-green
THHN and THWN wires are circuit wires that should never be handled when the circuits are turned on.
04 of 06
- Best for: Circuits requiring 50 volts or less
Low-voltage wiring is used for circuits typically requiring 50 volts or less. Several common types are landscape lighting wire, sprinkler system connections, bell wire (for doorbells), speaker system wires, and thermostat wires. Wire sizes range from about 22 gauge to 12 gauge, and these wires can be made of copper or aluminum. Low-voltage wires typically are insulated and may be contained in cable sheathing or combined in twisted pairs, similar to lamp cord wire. It must be used only for low-voltage applications. These are typically very small wires that are much different from standard circuit wiring, and their costs tend to be lower than other household wires.
Serious shocks rarely occur with low-voltage wires, but it is still always best to turn off devices before working with them.Continue to 5 of 6 below.
05 of 06
Phone and Data Wire
- Best for: Landline telephones and internet hookups
Telephone and data wiring are low-voltage wires used for “landline” telephones and internet hookups, typically made from copper. Telephone cables may contain four or eight wires. Category 5 (Cat 5) cable, the most common type of household data wiring, contains eight wires wrapped together in four pairs. It can be used for both phone and data transmission and offers greater capacity and quality than standard phone wire. Like low-voltage wire, it is often cheaper than other types of household wiring like NM or UF cables.
Although data wiring does carry a small amount of voltage, anything under 30 volts is generally regarded as safe (a household circuit carries about 120-volts of power). However, there is always a danger of data wiring coming into contact with household wiring, so you should treat it with caution and avoid touching bare wires.
06 of 06
- Best for: Data wiring
Coaxial cable is beginning to grow less common, thanks to the use of other forms of data wiring, such as HDMI, for television data transmission. Coaxial cable is a round, jacketed cable that features an inner conductor (usually copper) surrounded by a tubular insulating layer, surrounded by a tubular conducting shield made of braided wire. It can be identified by the threaded connectors that are used to make unions and device hookups.
Coaxial cable was once the standard for connecting televisions to antenna or cable service delivery and is still often used to connect satellite dishes or to bring subscription television service to an in-home distribution point. It typically has black or white insulation and is perfectly round in shape, making it easy to distinguish from NM electrical circuit cables. Coaxial cable can be found for affordable prices at most hardware and electronics stores.
The minuscule amount of voltage carried by coaxial cable signals makes it very unlikely to cause a shock of any type—provided the cables are not in contact with another source of current.
Choosing a Type of Electrical Wire
Whether you're replacing old wiring in your home or adding new electrical wires, it's important to choose the right type. Always select an electrical wire that is specified for the purpose you intend to use it for. For example, in wet locations outdoors, UF wire should always be chosen to ensure that your home's electrical system is protected from the elements. The amperage and volts of each wire should also be considered, and wires should be matched to the correct needs of every electrical project. If you're unsure which type of electrical wire you need, it's helpful to consult a professional electrician before installing any sort of electrical lines in your home.
Kuphaldt, Tony R. and John Haughery. Applied Industrial Electricity. Electrical Safety: How Much Electric Current is Harmful? Iowa State University, 2020.