Choosing the right type of electrical wire is critical for any electrical project. With so many options available, it can be confusing to decide which type of wire is best suited for the job. This comprehensive guide will walk through the six most common types of electrical wire and what applications each one is best for. We’ll also provide tips on how to select the proper wire gauge and insulation for your specific needs. By the end of this article, you’ll understand the key differences between the various wire types and feel confident choosing the right one for your next electrical wiring project.

Overview of the Main Options for Electrical Wire

There are two main categories of electrical wire – single conductor wires and multi-conductor cables. Single conductor wires have one solid or stranded metal conductor surrounded by insulation. Multi-conductor cables package multiple insulated wires together inside an outer protective sheath.

Within these two categories, the six most widely used types of electrical wire are:

Single Conductor Wires:

• Solid Core Wire
• Stranded Wire
• Aluminum Wire

Multi-Conductor Cables:

• Non-metallic (NM) Cable
• Armored Cable
• Underground Feeder (UF) Cable

Below we will examine each wire type in detail, including its composition, key features, and ideal applications. We’ll also provide guidance on selecting the proper size or gauge. First let’s start with some brief background on how wire is constructed.

Key Components of Electrical Wire Construction

All electrical wire and cable consists of two basic parts – the metal conductor surrounded by insulation:

• Conductor – Usually copper or aluminum, the conductor is the current-carrying part of the wire. Solid or stranded lengths of metal transmit power from the source to the load.
• Insulation – Made of plastic or rubber, the insulation prevents contact between wires and encloses the conductor. It also protects the wire from external damage. Insulation is color coded for circuit identification.

Additional components like fillers, bonding and grounding wires, sheathing and armoring may be incorporated into multi-conductor cables for added protection and performance.

Now let’s look at each of the six major wire types available and how they are designed and used.

Solid Core Wire

Conductor: Solid copper
Insulation: PVC or THHN

Key Features:

• Single solid conductor
• Rigid and stiff
• Used for permanent installations

Applications:

• Residential lighting and receptacles
• Switch legs and junction boxes
• Fixed wiring in appliances

Solid core wire, sometimes called solid conductor wire, contains a single solid copper conductor surrounded by a plastic insulating jacket. It is the most common type of single conductor wire used in residential and light commercial buildings.

Solid core wire is designed for permanently securing and routing through walls, conduit, and electrical devices. It is generally not used for applications where the wire will flex and move frequently. The rigid core can fracture and break from fatigue if repeatedly bent back and forth.

You’ll find solid core wire with insulation like PVC (polyvinyl chloride) and THHN (thermoplastic high heat-resistant nylon) in a range of colors for color coding and circuit identification.

For household applications, 12 and 14 gauge solid core wires are most common. Use 14 gauge for 15 amp circuit branches and 12 gauge for 20 amp small appliance circuits. Refer to local building codes for specific sizing requirements.

With its stiffness and stability, solid core wire works very well for installing new residential circuits, adding lighting fixtures, wiring appliances, and extending existing systems. It brings reliable power transmission to all areas of the home.

Stranded Wire

Conductor: Stranded copper
Insulation: PVC, THHN, TFFN

Key Features:

• Multiple flexible copper strands
• Easily bends and shapes
• Used for movable wiring

Applications:

• Extension cords
• Appliance power cords
• Low voltage control wiring
• Automotive, RV and boat wiring

For applications where wiring needs to move and flex repeatedly, stranded wire is the best choice. It contains multiple tiny copper wires twisted together to form a single conductor. The key benefit is flexibility – stranded wire can bend and shape without damage.

You’ll see stranded THHN wire used for wiring junction and outlet boxes during home construction. Since the solid core wires are joined inside the boxes, stranded wire allows easier manipulation of connections. Appliance cords and extension cords also utilize flexible stranded wire.

Standard sizes like 12, 14 and 16 gauge work well for most portable power applications. Stranded wire with super-flexible insulation like TFFN (thermoplastic flexible nylon) is excellent for automotive, marine, and RV wiring.

Anywhere loose, movable wiring is needed, flexible stranded wire should be the first choice. It safely withstands the twisting, bending, and vibration that solid core wire cannot tolerate.

Aluminum Wire

Conductor: Aluminum
Insulation: PVC, THHN

Key Features:

• Single solid aluminum conductor
• Lower cost than copper
• Used for large feeder circuits

Applications:

• Service entrance wires
• Feeders and subfeeds
• Large appliance and equipment wiring

Aluminum wire provides a more affordable alternative to copper for wiring large loads and carrying higher amperages. It costs less due to the lower market price of aluminum versus copper. While still used today, aluminum wiring faced some problems in the past with connections overheating and failing when improperly installed.

With advances in connection technology, aluminum wire has become a safe, reliable and cost-effective option for service entrance, feeder, and branch circuit wiring. Improved terminal fittings called COPALUM (aluminum/copper) create secure, corrosion-resistant connections between dissimilar metals.

Two key advantages make aluminum attractive – greater ampacity and lighter weight. For the same wire gauge, aluminum can carry nearly twice the load of copper. And it weighs about half as much per linear foot, making very large cables easier to install.

Common sizes for residential service entrance wiring are 2/0, 3/0 and 4/0 aluminum THHN cable. Wires above 6 AWG are generally aluminum. Use COPALUM anti-oxidant compound to prevent corrosion when terminating aluminum wires.

Non-Metallic (NM) Cable

Conductor: 2 to 4 insulated copper wires
Insulation: PVC
Sheath: PVC or nylon

Key Features:

• Multiple current carrying conductors
• Outer plastic sheath
• Staple cable

Applications:

• Residential and light commercial wiring
• Branch circuits, receptacles, switches
• Light fixtures, appliances, equipment

NM cable is the standard non-metallic multi-conductor wire used throughout residential and commercial buildings. It packages 2 to 4 insulated copper conductors together in a protective plastic sheath. The number of wires contained and color coding identifies use – for example 14/2 NM (2 conductors), 14/3 NM (3 conductors).

Being lightweight, flexible and easy to install, NM cable (often called Romex® cable) allows very efficient wiring in walls, ceilings, attics and crawlspaces. Since it eliminates the need to pull individual wires, installation time and cost is reduced. The non-conductive sheathing is thinner than conduit, requiring less space.

NM cable is subject to certain restrictions regarding exposure, securing and protection. It must be properly supported every 4.5 feet and within 12 inches of junction boxes. It should not be installed outdoors, on surfaces or in areas prone to physical damage.

The multiple conductors in NM cable make it convenient for wiring switches, receptacles and fixtures on a common circuit. Pick 14 or 12 gauge NM for lighting and outlet circuits, and 10 gauge for major appliances on 30 amp circuits.

Armored Cable

Conductor: 2-4 insulated copper wires
Insulation: PVC
Sheath: Galvanized steel or aluminum

Key Features:

• Interlocked metal armor sheath
• Moisture and crush resistant
• Requires no conduit or surface mounting

Applications:

• Wiring for commercial buildings
• Industrial environments, warehouses
• Mechanical rooms, electrical rooms

Armored cable provides extra protection with its interlocking spiral layer of galvanized steel or aluminum. The metal armor shields the conductors from damage from impacts, crushing, chemicals and moisture.

Since it can be run exposed without conduit, armored cable allows very flexible installation along walls, beams, joists and ceilings. The outer sheath connects to the ground bonding system for safety.

While more costly than NM, armored cable eliminates the labor expense of installing conduit for hard wiring commercial and industrial facilities. It meets code requirements for exposed wiring up to 10 feet in non-residential buildings.

Common sizes of armored cable range from 14/2 to 6/2 (2 to 6 conductors). Type AC cable has a smooth metal sheath, while Type MC has a corrugated armor for extra flexibility. Appropriate for feeder and branch circuits up to 600V and 100 amps.

Underground Feeder (UF) Cable

Conductor: 4 to 6 insulated copper wires
Insulation: XHHW
Sheath: PVC

Key Features:

• Moisture and sunlight resistant
• Direct burial in earth or concrete
• For outdoor trenches and conduit

Applications:

• Outdoor wiring to outbuildings
• Underground power distribution
• Street lighting, outdoor equipment

UF cable allows direct burial in the earth or concrete without conduit. The moisture-resistant insulation and rugged PVC jacket withstand exposure to wet locations, UV light and corrosive soils.

Also called underground feeder or USE cable, it commonly contains 4 to 6 THHN/THWN-2 copper conductors sized from 6 AWG to 2/0 for heavy feeder circuits. The large gauge wires handle up to 230/400V and currents to 400 amps.

PVC, XLP or XLPE insulation gives UF cable excellent dielectric strength and current-carrying capacity underground. Specialized applications like mining and drilling utilize high-quality UF cable for equipment wiring.

Bringing power to outdoor subpanels, outbuildings, pumping systems and landscape lighting is vastly simplified with direct burial UF cable. Use warning tape above the cable run to prevent future digging damage. Carefully follow minimum burial depth codes.

How to Determine the Correct Wire Size

Selecting the proper size or gauge of wire is critical for safe, effective power transmission and distribution at your intended electrical current. Follow these guidelines when choosing:

• Consider voltage – Higher voltages allow smaller wires; 120V systems normally use 14-12 AWG
• Evaluate required amp capacity – Consider the power draw; 15A for lighting, 20A for outlets, 30A for major appliances
• Factor length of run – Longer wire runs may require thicker wire to minimize voltage drop
• Check applicable codes for required sizes – NEC dictates insulation type, ampacity and load calculations
• Inspect electrical device terminals – Match wire size to device connection limitations
• Allow room for expansion – Upgrade wire gauge to handle potential increased future loads

In general, common wire gauges for household and light commercial use are:

• 14 AWG – 15 amp lighting and receptacle circuits
• 12 AWG – 20 amp small appliance and outlet circuits
• 10 AWG – 30 amp large electric appliances
• 8 to 6 AWG – Subpanels, EV chargers, heavy loads

Consult electrical codes to determine required wire sizes based on amperage rating, temperature rating and maximum overcurrent protection. Work from load calculations to select the optimal wire size and type.

Choosing the Right Insulation Material

For safe, long-lasting performance, the wire insulation must stand up to the electrical, physical, thermal, and environmental stresses of the application. Review these common insulation types when selecting electrical wire:

• PVC – All-purpose plastic insulation at a lower cost. Rated to 600V.
• THHN – For wet/dry locations. Flexible at high temps. Rated to 600V.
• XHHW – Extreme moisture resistance. Rated up to 2000V.
• SOW – Flexible rubber insulation. Heat/oil resistant. Rated 300V.
• TFFN – Very flexible Teflon for high movement wiring. Rated to 600V.
• SIS – Extreme cold rating for outdoor insulation.
• MI – Mineral insulation for high temperature resistance.

Match the insulation to the conductor material, electrical load, environmental factors, and mechanical stress. Ensure it meets or exceeds local electrical code requirements.

Safety Tips for Electrical Wiring

• Turn power OFF at the breaker box before starting any work
• Use caution when wiring near hot wires, terminals and connections
• Wear appropriate PPE – insulated gloves, eyewear, sturdy shoes
• Keep wiring tidy, tight and properly terminated
• Avoid kinks, strains and sloppy connections which can cause shorts
• Use circuit protection devices – fuses or breakers for overload safety
• Separate wires of different voltages and colour code for identification
• Install to code including proper grounding, conduit fill, and wire support

Conclusion

We’ve examined the six most common types of electrical wire – solid core, stranded, aluminum, NM, armored, and UF cables. By understanding the construction, ratings, and intended applications of each, you can knowledgeably select the right wiring solution. Matching the wire size and insulation to your specific electrical demands ensures optimal safety and performance. Use the proper techniques for installing and terminating wires, cables and connections. Follow all electrical codes and utilize circuit protection devices. With the information in this guide, you’ll be able to wire lights, outlets, appliances and equipment with confidence.

Frequently Asked Questions

Below are some common questions about types of electrical wires to help clarify key points:

What is the most common wire for residential electrical use?

Solid core wire with THHN insulation is generally the most widely used for lighting circuits, receptacles, appliances etc. in homes and apartments. 12 and 14 gauge solid core copper wire works for most basic household applications.

What type of wire do electricians use for house wiring?

Electricians typically use a combination of single solid core wires secured in conduit and NM cables when wiring a residential building. NM cables are quick and convenient between boxes, while solid core establishes permanent runs and circuits.

Can extension cords have solid core wire?

Solid core wire is too stiff and prone to breakage when flexed repeatedly. Extension cords should always utilize stranded wire which is designed for flexibility and handling. Stranded THHN and SJOW cable are common.

What is the difference between copper and aluminum wiring?

Copper wiring is more expensive but has higher ampacity for the same gauge size. Aluminum is lighter in weight and costs less, but requires special terminations to avoid oxidation. Larger aluminum wires are commonly used for service entrance and high load feeders.

Is aluminum wire safer now than in the past?

Yes, improved connection methods and anti-oxidant compounds have made aluminum wiring safer and more reliable than decades ago. CO/ALR connections prevent overheating failures that sometimes occurred with outdated installation practices.

Can NM cable be run outdoors?

No. Plastic-sheathed NM cable is only approved for indoor applications, protected from weather and damage. Outdoor wiring requires moisture-resistant conduit and conductors like UF cable.

When should I use armored cable versus NM cable?

Armored cable is an upgraded alternative to NM cable for commercial and industrial sites where wiring may be exposed and subject to damage. Its metal armor withstands harsh conditions that would penetrate NM sheathing.

What are the main components of UF cable?

UF cable contains 4-6 THHN/THWN-2 copper conductors rated for wet locations. It is insulated with XHHW polyethylene and sheathed in a rugged sunlight-resistant PVC jacket for direct burial without conduit.

Why is insulation important for electrical wires?

Insulation prevents current flow and short circuits between individual wires and other conductive surfaces. It also protects against moisture damage and withstands electrical, thermal, and mechanical stresses. Insulation resistance and dielectric strength preserve safe operation.

How do I determine the correct wire size for a circuit?

Consider the circuit voltage, current load in amps, length of run, number of conductors, allowances for expansion, and applicable electrical code requirements. These factors dictate the proper wire gauge to safely handle the electrical load according to NEC standards.

What is the minimum size electrical wire for a 15 amp circuit?

For a typical 120 volt 15 amp circuit like household lights and outlets, the NEC requires a minimum of 14 AWG copper wire with insulation rated for at least 75°C. This helps ensure protection against overheating with 15 amp overcurrent devices.