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.
Wiring Terminology
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). 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. 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. 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: ThermoplasticH: Heat-resistant; HH means highly heat-resistantW: Rated for wet locationsN: 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, orangeNeutral wires: White, brownGround wires: Green, yellow-green
THHN and THWN wires are circuit wires that should never be handled when the circuits are turned on. Serious shocks rarely occur with low-voltage wires, but it is still always best to turn off devices before working with them. 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. 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.
