Electrical wire and cable must be sized and installed correctly to pass an electrical inspection and keep electricity running safely through your home. This guide will teach you the difference between types of electrical wires and types of electrical cables. You’ll also learn how to choose between electrical cables and wires for your projects.
Tip: To calculate the maximum wattage your wire or cable can hold, multiply amperage by voltage.
- Amps x voltage = watts.
- Amperage: strength of an electrical current
- Voltage: electrical force needed to drive a current between two points
- Wattage: amount of electricity used
Wire Vs. Cable
While the terms wire and cable are often used interchangeably, a wire is one electrical conductor and cable is multiple conductors, or a group of wires, encased in sheathing.
Electric wires are typically made of aluminum or copper. They are either bare or insulated and typically covered in a thin layer of PVC. If they have a PVC sheath, then the PVC is colored to indicate whether the wire is a neutral, ground or hot wire in your electrical installation. We discuss wire colors in its own section in this guide.
Cables contain at least a neutral wire, ground wire and hot wire that are twisted or bonded together. Depending on its purpose, the cable may contain more wires. The wires in a cable are insulated in their own color-coded layer of PVC. The group of wires is then encased in an outer sheath to make up the single cable.
Safety: The National Electrical Code (NEC) and local building codes regulate the types of electrical wires 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 electrical wiring and cable 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.
Tip: If many electrical conductors are bare and twisted together without insulation, they are still considered one conductor and classified as a single “wire” rather than a cable.
The information printed on the sides of wire indicates its THHN/THWN, material, max voltage rating and gauge.
THHN/THWN letters represent the most common types of electrical wires used in residential applications. Look for these letters on wire packaging to know what qualities the wire has:
- T – Thermoplastic insulation
- H – Heat resistant
- HH – High heat resistance up to 194-degrees Fahrenheit
- W – Rated for wet locations
- N – Nylon-coated to resist damage from oil or gasoline
- X – Synthetic polymer, flame-resistant
Most wire will be marked “CU” for copper, the most common conductor of residential electricity. Because electricity travels on the outside of copper wire, these wires are insulated to protect against fire and shock.
Aluminum wire is more conductive than copper wire, but it also degrades faster. For this reason, aluminum wire typically isn’t used in homes. Older wire could be aluminum or copper-clad aluminum. To comply with NEC guidelines, aluminum wire should only be installed by a professional electrician.
Maximum Voltage Rating
The maximum voltage rating will be a number such as 600, which indicates the maximum voltage the wire can carry. For safety purposes, stay around 80-percent of the max wattage your gauge can carry.
The wire gauge indicates the electrical wire sizing, as defined by the American Wire (AWG) system. The most common gauges are 10, 12 or 14. The gauge and diameter of the wire are inversely related. In other words, as the gauge number gets higher, the diameter of the wire gets smaller. For example, a 10-gauge wire is bigger than a 12-gauge wire. Larger wires can carry more amperage and wattage than smaller wires.
The below electrical wire sizing chart shows both the recommended 80-percent wattage load and the absolute maximum 100-percent wattage load for the most common wire gauges. The chart also tells you the recommended uses for each gauge.
Tip: If a project calls for longer lengths of wire (such as 80 or more feet from the breaker), increase the gauge size to ensure that enough electricity can pass through it.
Recommended Wattage Loads
A wire’s color tells you the purpose of the wire. Typically, white wires are neutral wires, green or bare wires are ground wires and any other color is a hot wire that carries an electrical current.
- White insulation: Typically considered neutral but can sometimes be used as a hot lead in certain situations, such as switch loops. In existing wiring jobs, white wires may also be marked with black or red to indicate that it’s now a hot wire.
- Green insulation and bare copper: Ground wire.
- Black insulation: Hot wire for switches and outlets.
- Red insulation: Hot wire for switch legs and hardwired smoke detectors
- Blue/Yellow insulation: Hot wire pulled through a conduit
Safety: A neutral can be just as dangerous as a hot wire, with the potential to electrocute you or to "ground out" and electrify any metal it meets. Treat every wire as though it’s a hot wire. If you have any uncertainty as to whether a white wire is used as neutral or hot in a project, check with a professional electrician.
Types of Electrical Cable
Different types of electrical cables each have their own specific purposes and applications. Below are common cables you may use in your projects:
- “NM” stands for non-metallic, which refers to the flexible, typically PVC sheathing surrounding the cable. “B” indicates a heat rating of 194-degrees Fahrenheit, ensuring that its interior wires can operate at certain levels without overheating.
- Most common form of indoor residential electrical wiring.
- Inside the sheathing are at least two thermoplastic insulated wires of the same gauge, though different cables can have different gauges.
- For indoor use only, in spaces free from moisture and away from any heat sources. Do not bury or run outside of a wall.
- Best used behind walls and ceilings and inside floor cavities.
- ”UF” stands for underground feeder; rated for in-ground and damp-area installation.
- 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.
- “AC” means armored cable. Also known as “BX.”
- Consists of insulated hot and neutral wires and a bare bonding wire, all wrapped in paper.
- Wire enclosed in metal sheathing that acts as the grounding conductor.
- Relatively expensive and difficult to work with. Often found in older homes but not used in new builds.
- For indoor use only.
- Similar to AC, but wires are wrapped in plastic instead of paper.
- Has green grounding wire because its metal sheathing can’t be used as a ground.
- For indoor use only.
- Not often used in residential applications.
- Usually called “coax.”
- Metallic cable often used to carry television signals and connect video equipment.
- Features central wire conductor covered with a dielectric or non-conducting insulator. The insulator is surrounded by mesh or a metal sheath and covered by a thin plastic layer for protection.
- Rubber cable often used to transmit digital video, multi-channel surround audio and advanced control data through a single cable.
- An all-digital audio-video interface which carries signals in uncompressed format.
- HDMI connector types: Type A/B are defined in the HDMI 1.0 specification, type C is defined in the HDMI 1.3 specification, and type D/E are defined in the HDMI 1.4 specification.
- Used to make the electrical connection between loudspeakers and audio amplifiers.
- A zip-cord type of electrical cable where two or more electrical conductors are individually insulated in a plastic or rubber that can be easily pulled apart.
- Usually called “cat-5e” or ethernet cable.
- Industry standard for unshielded twisted-pair cables (UTP) for connecting phone, computer, home automation and A/V networks.
- Copper cabling typically consists of 4 pairs of wire (8 total conductors) wrapped in a single jacket.
Tip: Both NM and AC cable require special cutting tools that cut the sheathing but not the internal wires. They also require bushings inserted in the ends to prevent the sharp edges of the metal from damaging the wires, as well as special electrical boxes and connectors.
All the information you need to know about a type of cable is printed on its sheathing.
- Type: Will list the type of cable, such as NM-B or UF.
- Gauge: The gauge of the individual wires inside the cable, such as 14, 12, 10, etc.
- Number of wires: This number follows gauge. For example, 14/2 indicates that there are two 14-gauge wires (a ground wire, if part of the cable, is not included in this number) within the cable.
- Grounding: The word “GROUND” or the letter “G” indicates the presence of a ground wire.
- Voltage rating: The most common rating for residential use is 600-volts but this can vary. The number indicates the maximum voltage the cable can safely carry.
- UL: Indicates that the cable is safety certified and approved for use by Underwriters Laboratories.
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