Knowing the basic electric wire types is essential to almost any electrical project around the house. When you're installing new wiring, for example, choosing the right wire or power cable is half the battle. And when you’re examining existing wiring in your home, identifying the wire type can tell you a lot about the circuit the wiring belongs to—for example, when 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.
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).
THHN and THWN are codes for the two most common types of insulated single core wire used inside the conduit. Unlike NM cable, in which two or more individual insulated conductors 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. The letters indicate specific properties of the wire insulation:
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. Low-voltage wires typically are insulated and may be contained in cable sheathing or combined in twisted pairs, similar to lamp cord wire and flat cable. It must be used only for low-voltage applications. These are typically very small wires that are much different from standard circuit wiring.
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).1 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 electric cable.
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 surrounded by a tubular insulating layer, surrounded by a tubular conducting shield made of braided multi-core wire. It can be identified by the threaded connectors that are used to make unions and device hookups.