Types of Electrical Wires and Cables

The most common types of electrical wires used in residential applications are usually nylon coated thermoplastic with a high-heat resistance. Wires are labeled with the THHN/THWN, material, maximum voltage rating and gauge. 

• THHN/THWN

Here’s what the letters stand for:

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 

THHN is made for temperatures up to 75 degrees Celsius. THWN can usually handle higher temperatures in both dry and wet conditions.

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. 

The maximum voltage rating will be a number such as 600, which indicates the maximum voltage the wire can carry. The average household voltage is 120 to 240 volts.

To calculate the maximum wattage a 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

A wire’s color tells you the purpose of the wire. The NEC references the white conductor as the grounded conductor, the green or bare as the equipment grounding conductor, and the other colors as the ungrounded conductors. Typically, white wire is neutral wire and green or bare wire is ground wire. Any other color is usually 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 Tip: Always test wires with a volt checker. A neutral can be just as dangerous as a hot wire. It still has the potential to electrocute you. It can also "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. 

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. 

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. 

The below electrical wire sizing shows both the recommended and the most common wire gauges. Here are the recommended uses for each gauge.  

Wire and Cable Gauge: 14-gauge

• Recommended 80 Percent Wattage Load: 1440 watts (120 volts)
• Max Wattage Load: 1800 watts (120 volts)
• Recommended for common residential wiring: Light fixtures, household receptacles

Wire and Cable Gauge: 12-gauge

• Amps: 20
• Recommended 80 Percent Wattage Load: 1920 watts (120 volts), 3840 watts (240 volts)
• Max Wattage Load: 2400 watts (120 volts), 4800 watts (240 volts)
• Common residential wiring: Light fixtures, household receptacles, small appliances

Wire and Cable Gauge: 10-gauge

• Amps: 30
• Recommended 80 Percent Wattage Load: 2880 watts (120 volts), 5760 watts (240 volts)
• Max Wattage Load: 3600 watts (120 volts), 7200 watts (240 volts)
• Large household appliances: Window air conditioner units, clothes dryers

Wire and Cable Gauge: 8-gauge

• Amps: 40
• Recommended 80 Percent Wattage Load: 7680 watts (240 volts)
• Max Wattage Load: 9600 watts (240 volts)
• Large household appliances: Electric ranges, central air conditioning

Wire and Cable Gauge: 6-gauge

• Amps: 55
• Recommended 80 Percent Wattage Load: 10560 watts (240 volts)
• Max Wattage Load: 13200 watts (240 volts)
• Large household appliances: Central air conditioning, electric furnace

All the information you need to know about a type of cable is printed on its sheathing. Use the following to determine if a cable is right for a project:

• 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 and more.
• 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.

There are several different types of electrical cables. Each have their own specific purposes and applications. Below are common types of electrical cables used in homes and businesses:  

NM-B Cable 

• “NM” stands for non-metallic, which refers to the flexible, typically thermoplastic 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 Cable 

• "UF” stands for underground feeder; rated for in-ground and damp-area installation.
• Looks like an NM-B cable, but the wires are embedded as a group in solid thermoplastic (rather than individually encased in flexible thermoplastic).
• Like an 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 

• “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.

Metal-Clad Cable

• 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.

Coaxial Cable 

• Usually called “co-ax.”
• 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.

HDMI Cable

• 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.
• Cost-effective.
• 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 is defined in the HDMI 1.4 specification.

Speaker Cable 

• 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.

Category 5e Cable 

• 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.

Lamp Wire 

• SPT-1 and SPT-2 is intended for use in small household appliances, including lamps, clocks and fans.
• Not subject to hard usage.
• SPT-1 and SPT-2 conductors are rated for use up to 105 degrees Celsius.

Landscape Cable

• May be used as low-voltage (low-energy) underground.
• Security and outdoor accent lighting applications.
• Not to exceed 150 volts when installed as specified by the National Electrical Code® (NEC) and other applicable standards.
• Sunlight and UV resistant.
• Suitable for direct burial.
• For use at temperatures between -20 degrees Celsius and 60 degrees Celsius.
• Copper conductors.

Sprinkler System Cable 

• May be used for connecting field and central controls up to 30 volts.
• Available with 4, 5, 7 or 10 copper conductors and in 50-, 100- and 500-foot lengths.
• Sunlight resistant and suitable for underground applications.
• Insulation rated at 60 degrees Celsius.

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. Special electrical boxes and connectors are also required.