Wire and cable make up the delivery system for electricity in your home. Running from the main breaker panel or fuse box to outlets, appliances and fixtures indoors and out, wire and cable must be sized and installed appropriately to keep electricity running through your home—and to pass an electrical inspection.
While the terms wire and cable are often used interchangeably, technically wire is one electrical conductor and cable is a group of conductors, or wires, encased in sheathing. The National Electrical Code (NEC) and local building codes regulate the types of wire and cable that can be used in specific electrical applications, as well as the manner of installation. Check with your local building inspector before you start any wiring and cable electrical project and be sure to obtain required permits. When your work is complete, always have it inspected for compliance with local codes to ensure that it has been safely installed.
This buying guide will explain the different types of
wire and cable and their uses, so you can feel confident you’re making the
best and safest selection for the electrical system in your home.
Factors to Consider
THHN or THWN
– These letters represent the most common types of individual wires used in
residential applications. The letters represent the following NEC
• T is for the thermoplastic insulation on the wire;
• H is for heat resistance;
• H is for high heat resistance up to 194° Fahrenheit;
• W means the wire is rated for wet locations, such as outdoors; and
• N means the wire is impervious to damage from oil or gas.
Material — Most wire will be marked “CU,” for copper, the most common conductor of residential electricity. Because electricity travels on the outside of copper wire, wires are insulated to protect against fire and shock. Older wire could be aluminum or copper-clad aluminum.
Maximum voltage rating — This will be a number such as 600, which indicates the maximum voltage the wire can carry.
Gauge – This number indicates wire size. The most common gauges are 10, 12 or 14. Larger numbers represent smaller sizes or gauges of wire. See the table below for more about wire and cable gauge.
Colored insulated wires other than white or green are always hot. Black, blue and red wires are typical hot wires in residential wiring.
White insulated wires are always neutral.
Green insulated and bare copper wires are always ground wires.
Run wires in conduit for unfinished areas such as basements or attics and outdoors for devices like landscape lighting. To learn more about conduit, see our Conduit Buying Guide
NM-B cable is the most common form of indoor residential electrical wiring. The “NM” stands for non-metallic, which refers to the flexible, generally PVC sheathing surrounding the cable. The “B” represents a heat rating of 194° Fahrenheit. This rating ensures wires can operate at certain levels without overheating, melting the insulation and creating fire and safety hazards. Inside the sheathing are at least two thermoplastic insulated wires of the same gauge, though different cables can have different gauges. As with wire, all the information you need to know about NM-B cable is printed on the sheathing.
Wire is sized by the American Wire Gauge (AWG) system. The larger the number the smaller the wire. The following table provides information about amps (the amount of current a wire can safely carry), and wattage (the rate of electrical energy used by an appliance), and common uses of different gauges of wire and cable.
Run NM-B cable behind walls and ceilings, inside floor cavities and in other
unexposed areas. It is not designed for running along the outside of a wall,
such as in an unfinished basement. Use NM-B indoors only, in spaces that are
dry and free from moisture. Exposure to water can subject the wires to
corrosion. Since the insulation is rated to handle only a certain level of
heat, you’ll want to avoid placing wires near heat sources such as hot water
pipes or heating ducts. Also, do not bury NM-B in cement, concrete, plaster or
UF cable is similar to NM cable, but is rated for in-ground and damp-area installation. In fact, UF stands for underground feeder. From the outside UF cable looks like NM-B cable, but the wires are embedded as a group in solid thermoplastic (rather than individually encased in flexible thermoplastic). Like NM cable, UF cable comes in a variety of gauges to meet all electrical code requirements and is labeled with the same information carried on NM cable plus the designation UF.
Armored cable (AC)
is wire enclosed in metal sheathing. Often called by the trade name, BX, AC
consists of insulated hot and neutral wires, plus a bare bonding wire, all
wrapped in paper. The metal sheathing acts as the grounding conductor. AC is
relatively expensive and difficult to work with, so it’s not often used in new
residential construction. It can be found in older homes, however. AC is rated
for indoor use only.
Metal-clad cable is similar to AC, except that the wires are wrapped in plastic rather than paper. In addition, MC cable has a green grounding wire, because its metal sheathing can’t be used as a ground. MC cable is rated for indoor use only, though, like AC, it’s not often used in residential applications. Both MC cable and AC require:
Special cutting tools, which cut the sheathing but not the wires;
Bushings, which are inserted in the ends to prevent the sharp edges of the metal from damaging the wires; and
Special electrical boxes and connectors.
Coaxial cable, usually called coax, is a metallic cable most often used to carry television signals and connect video equipment. Coax features a central wire conductor covered with a dielectric or non-conducting insulator surrounded by mesh or a metal sheath and covered by a thin plastic layer for protection. For more information on coax, see our Networking Cables Buying Guide.
Category 5e cables, also called cat-5e, are the industry standard for unshielded twisted-pair cables (UTP) for connecting phones, computer networks, home automation networks and audio/video distribution systems. Often generically called Ethernet cable, the copper cabling typically consists of 4 pairs of wire (8 total conductors) wrapped in a single jacket. For more information on cat5-e cable, see our Networking Cables Buying Guide.