The Basics
First, understand the difference between wire and cable:
- A wire is one conductor that carries an electrical current through a circuit.
- A cable is a collection of wires sheathed together.
The majority of conductors are copper, which is corrosion-resistant and works as a better conductor than aluminum. Aluminum serves as a less expensive, lightweight alternative.
The American Wire Gauge (AWG) system provides standard wire gauge sizes. The higher the number of the gauge, the smaller the size of the wire. See the AWG chart below for examples. The National Electrical Code (NEC) mandates the regulations for wire and cable that can be used for electrical applications.
Key Definitions
- Amperage: a measurement of electric current
- Voltage: the difference in electrical potential between two points
- Voltage Drop: the difference between measurements at each terminal of a device
- Wattage: how much electrical energy is used
Follow the manufacturer's instructions for installation and safety. Check to see if you need a permit. Observe applicable building and electrical codes. Contact a licensed electrician if you have any doubts or questions about the connections or if your home's wiring doesn't appear compatible with the changes you're making.
Wire Amperage Chart
Wire Gauge Chart
How to Identify Wires and Cables
Each jacket will have information printed on it to help you choose the correct product for your job. A letter code provides the attributes of the wire, along with material, gauge and voltage rating.
Naming and Taxonomy
The NEC provides a system with letters to quickly identify what a wire’s capabilities are. Some common lettering for wire includes THHN, XHHW, THW, TFNN, etc.
Thermoplastic flexible fixture nylon (TFFN) wire works best for fixtures, appliances, control circuits and machine tool wiring (MTW). This is because it’s a stranded conductor, making it highly flexible and easily attachable to other surfaces. TFFN wire withstands temperatures up to 90 degrees Celsius in dry environments and up to 60 degrees Celsius in wet conditions. It’s also oil-resistant. This makes it suitable for both indoor and outdoor environments.
Thermoplastic high-heat-resistant nylon (THHN) wire is optimal for carrying high loads of electrical current of up to 600 volts in commercial and industrial settings. Its high heat designation makes it a fantastic conductor since it can withstand temperatures up to 90 degrees Celsius for extended periods. However, this type of wire is fragile because it only has one protective layer. You should place THHN wire into a conduit before burying it to prevent damage.
Thermoplastic heat- and water-resistant nylon (THWN) wire also works well in commercial and industrial settings. It conducts up to 600 volts, although it’s not uncommon to find types that conduct as little as 110 volts. It’s very durable and resistant to water and oil. THWN wire can operate in wet environments for extended periods without losing performance. It can also withstand temperatures up to 90 degrees Celsius. THWN wire is one of the best choices for electricians because of its durability and versatility for both indoor and outdoor settings.
Below are the letters and attributes you’ll see regularly in residential wiring:
- T: thermoplastic insulation
- FF: flexible fixture
- H: heat resistance
- HH: high heat resistance (up to 194 degrees Celsius)
- W: suitable for wet locations
- N: nylon coating, resistant to damage by oil or gas
- X: synthetic polymer, flame-resistant
THHN vs. THWN Wire and Cable
THHN and THWN wire types are both suitable for industrial settings. They’re water-resistant, conduct up to 600 volts and can withstand temperatures up to 90 degrees Celsius. However, the key difference is in their durability. THWN wire is much better at resisting moisture and won’t suffer drops in performance if exposed to water for extended periods. THHN wire is better at resisting hot temperatures for long durations, but it’s not ideal for maximizing performance in wet climates. It’s also thinner and more fragile, meaning you should place it into a conduit before use. Consider THHN wire when you need maximum performance in dry climates and have heavy electrical loads that produce a lot of heat.
Wire Colors
A wire's coloring is important as an industry standard to identify a wire's purpose. This is helpful for the next electrician coming to a jobsite and for an advanced DIYer who plans to do some electrical work on their own. Don't assume a wire isn't hot because of its color. All wires have the capability to carry a load and may have been connected differently from the industry standard.
- Black: Hot wire for switches or outlets
- Red: Hot wire for switch legs and connecting to hardwired smoke detectors
- Blue and Yellow: Hot wires pulled through conduit; blue is often used for three- or four-way switch applications, and yellow is for switch legs to control fans, lights, etc.
- White: Neutral (can be hot if marked with black or red to indicate it's no longer a neutral)
- Green and Bare Copper: Only for grounding purposes
Color-Coded Jackets for NM-B
Another industry standard that’s been accepted over the years is color-coded jackets for non-metallic, or NM-B, wire (also commonly referred to as Romex, building wire or NM). Similar to how specific wires are color coded, colored sheaths provide an easy identifier for what gauge the wires inside are.
- White: 14-gauge wire, primarily used for lighting circuits
- Yellow: 12-gauge wire, which is used regularly in households for general power to outlets and most appliances
- Orange: 10-gauge wire, commonly run for air conditioners and water heaters
- Black: 8-and-lower-gauge wire, used for feeding a subpanel, electric range, oven, etc.
Types of Cable
Armor-Clad (AC) Cable: AC cable includes THHN-insulated conductors with 16-gauge aluminum bond wire placed inside the armor to act as a grounding conductor.
Automotive Cable: This is a general-purpose thermoplastic (GPT) wire, also referred to as primary wire. Normal applications are within motor vehicles with limited exposure to fluids, physical wear and abuse.
Bayonet Neill-Concelman (BNC) Cable: BNC cables are small, quick-connect/disconnect radio frequency connectors used for coaxial cables.
Category Cable: This is used for phone systems and data networking systems. Cat 5e is the most common variety of category cable that’s used for computer networking on internet service installations. The conductor pairs are twisted together to prevent cross-talk and interference from other paired conductors in the cable, as well as external interference. The higher the megahertz (MHz) capability, the more twists per foot.
Coaxial Cable: This is a metallic cable that carries television and video signals. It connects to video equipment and features a central conductor with a dielectric insulator, metallic shield and plastic jacket.
Doorbell Wire: Doorbell wire is used to connect a wired doorbell or video doorbell to a home’s electrical system. 18-gauge wire is the variety most often used.
Dual Armored Cable: This is a durable cable that offers protection without employing electrical conduit, elbows, offsets (which can be expensive) or conduit couplings. For areas where the cable may be exposed to moisture, metal-clad armor prevents corrosion.
Flexible Cord: Typically used for industrial machinery, washing machines and large appliances, portable tools, equipment, and extension or power cords, flexible/power cord has its own naming convention based on a letter code, with a common option being SJEOOW.
- S: service cord (when not followed by a J, V or P; also indicates a rating of 600 volts)
- J: junior service cord, 300 volts
- T: thermoplastic
- E: elastomer, thermoplastic that looks and feels like rubber
- O: oil-resistant outer jacket
- OO: oil-resistant outer jacket and oil-resistant insulation
- P: parallel cord (light duty, flat)
- V: vacuum cleaner cord (light duty, round)
- W: sunlight- and moisture-resistant
Lamp Cord: Used with lamps, small appliances, radios and other similar products that don’t exceed 300 volts, lamp cord is available between 18- and 12-gauge sizes in a variety of colors.
Landscape Lighting Low-Voltage (LV) Cable: This underground cable is suitable for outdoor accent lighting, landscape lighting and security lighting. Applications shouldn’t exceed 150 volts. It’s used for direct burial, is suitable for sunlight and is available between 16- and 8-gauge sizes.
Metal-Clad (MC) Cable: MC cable is used heavily in commercial electrical work, for running through concrete or in other commercial environments. Individual THHN wire conductors are run through an aluminum interlocked armor. It includes a grounding wire.
Mobile Home Feeder: This connects a mobile home to a supply of electricity where permanent wiring is required, and it’s suitable for direct burial and underground service entrance cable. It includes four RHH or RHW-2 conductors, with a white stripe for neutral and a green ground conductor. It’s sunlight-resistant.
Network and Data Cable: This comes in three types — fiber-optic, twisted-pair and coaxial cable — and is used to connect multiple networking devices or computers in a network.
NM-B: This is a non-metallic sheathed cable that’s used as a residential building wire for branch circuits for outlets, lighting and other residential applications. NM-B is available between 14 AWG and 6 AWG with two or three conductors.
Preassembled Whips: These are pre-cut lengths of armored cable designed to increase jobsite productivity. Assembly comes with pre-stripped THHN conductors and pre-installed zinc die-cast, snap-in fittings.
Residential Grounding Wire: This is bare copper wire that’s available in 4-, 6- and 8-gauge solid and stranded construction. It’s used to ground the residential electrical system, usually at the meter before it enters the dwelling. It’s also used for grounding the perimeter surface around pools.
Service Entrance Cable: This includes individual conductors rated XHHW-2 or THHN/THWN and feeds power from a main breaker to a subpanel. It can be exposed to direct sunlight and used in wet or dry locations.
- SE-R: Twisted together with a bare ground, SE-R is used to bring service from the panel to other panels in multiple-unit dwellings and in SE-U purposes.
- SE-U: Bare conductor strands are helically wound about the two paralleled insulated conductors. It’s used for single-family residential buildings to convey power from the service drop to the meter base and from the meter base to the distribution panel board.
Speaker Wire: Made of copper and designed to transport a low-voltage electrical current, speaker wire has a variety of wiring uses, including doorbells, thermostats, home security sensors, landscape lighting and other low-current systems.
Sprinkler Wire: Multi-conductor sprinkler wire is suitable for direct burial on applications up to 30 volts. It’s used in central controls for underground sprinkler systems and is available in 18-gauge construction with up to 25 conductors.
Submersible Pump Cable: This includes THWN copper conductors that are heat-, moisture-, oil- and gasoline-resistant. It’s suitable for temperatures below 75 degrees Celsius with two or three conductors. It’s used for power and circuits for submersible pump systems.
Thermostat Wire: Used in heating and air conditioning systems, along with bell and alarm systems, thermostat wire is available in 20- or 18-gauge sizes with up to 10 conductors.
Underground (UF-B) Wire: A copper wire used for underground purposes, including direct burial, it comes in a gray jacket and can be used for deck lighting, outdoor water features, landscape lighting and air conditioner compressors.
Underground Residential Distribution (URD) Cable: Used for secondary distribution and underground service applications at 600 volts or less, it’s suitable for direct burial or placement in ducts. It’s acceptable in wet locations in triplex or quadruplex. Conductors are stranded, compressed aluminum. The neutral conductor has a yellow, triple-extruded stripe.
With potentially life-threatening dangers involved with mishandling electrical wire and cable, it's of the utmost importance to follow all safety guidelines and precautions, and to understand how electricity works. If you have any doubt about your ability to safely handle a project, seek professional assistance to complete the job properly. Always follow the manufacturer's recommendations on using cables.
Tools and Accessories
When completing an electrical project, it’s important to have the right tools and safety equipment to get the job done. Check out some of the most common tools for an electricians tool box.
Boxes and Covers: These are used to house outlets and adapters for operating lights, ceiling fans, kitchen appliances, etc.
Circuit Breakers and Fuses: These are two devices for preventing an electrical current from causing damage by overloading or shorting a circuit. Breakers and fuses interrupt the current during an overload or short and are housed in a breaker box or fuse box. Homes built after the 1960s typically use circuit breakers rather than fuses.
Electrical Tape: Used for repairing electrical cords or insulating a wire, electrical tape is typically black. It can be used to identify wires and should be stretched as you apply it for better adherence.
Electrical Testers: Checking a circuit to make sure it isn’t live can be a life-saving decision. An electrical tester will quickly inform you if you’re working with live cables or not.
Outlets and Adapters: When wires are connected to an outlet or adapter, it allows the electrical current to power anything plugged into it, such as a kitchen appliance.
Plugs and Connectors: These are usually run from an appliance or a power cord and are plugged into an outlet on the wall. They allow an appliance to receive power from an outlet.
Wire Connectors: These connect two wires together with a connector: The exposed end of each wire is put into the connector and twisted so that they’re connected. Check out our DIY Basics video: How Do I Connect Two Wires?
Wire/Cable Cutters: This tool is used to cut directly through wire and cable. There are a variety of cutters for different jobs, so check that you’re using the appropriate one, whether you’re cutting through copper wire or a network cable.
Wire Strippers: This device removes the plastic casing to expose the bare wire underneath. Most strippers offer multiple slots for a variety of wire sizes, while some have an adjustment dial to set the correct size. Simply insert a wire into the correct sized slot, twist and pull it through.