Wire Types and Sizes

 The American Wire Gauge (AWG) system is a standardized method used to measure wire sizes in the U.S. This system assigns a numerical gauge value to wires based on their diameter, where a lower AWG number indicates a thicker wire, capable of carrying more current. For instance:

• 14 gauge wire, one of the smallest sizes used in residential wiring, is typically rated for 15-amp circuits and used for lighting and standard wall outlets.
• 12 gauge wire, which is thicker, can handle 20-amp circuits and is often used for kitchen and bathroom receptacles, where appliances like toasters or hairdryers may demand more current.
• 10 gauge wire is designed for 30-amp circuits and is used in circuits for larger appliances, such as electric water heaters, clothes dryers, and air conditioning units.

As wires get larger and thicker, they can handle increasingly high current levels (ampacity). The largest wires, called 1/0, 2/0, 3/0, and 4/0 (pronounced “one-ought,” “two-ought,” etc.), are used in service panels to provide power to entire buildings. For example:

• A 1 AWG wire is common for 150-amp main breakers.
• For 200-amp service panels, a 2 AWG grounding wire is often used along with heavier conductors, ensuring safety and durability for high-load applications.

2. Solid vs. Stranded Wire Structures

The structure of a wire affects its flexibility and durability. Smaller wires (14, 12, and 10 gauge) are typically available in both solid and stranded forms:

• Solid wire, or single-strand wire, is common in residential wiring as it is flexible enough to handle regular electrical tasks and holds its shape well, making it easy to install in walls and outlets.
• Stranded wire consists of multiple smaller strands twisted together. This structure is preferred in applications requiring frequent movement or flexibility, such as appliances that may be moved around. Stranded wire is more flexible than solid wire but is usually more expensive due to the manufacturing process.

For larger gauges (8 AWG and above), wire is typically stranded by default, as a solid conductor of that size would be too rigid to work with easily. Standard stranded constructions include:

• 7 strands for larger wires like 8 to 2 AWG.
• 19 strands for wires 1 AWG and larger, providing additional flexibility even at high diameters.

In specialty applications, such as welding cables, wires are constructed with hundreds of fine strands to achieve maximum flexibility, allowing easy maneuvering of welding tools without risking wire breakage.

3. Insulation Codes and Characteristics

Insulation around wires serves as a protective barrier, preventing electrical shorts, protecting the wire from environmental damage, and ensuring user safety. Common insulation codes, such as THHN, THWN, and XHHW, indicate the type and properties of insulation materials:

• T stands for thermoplastic, typically PVC, which is common in residential wiring.
• X indicates cross-linked polyethylene (XLPE), which is more durable and can withstand higher temperatures than PVC.
• H represents heat resistance, with HH denoting a higher heat tolerance, up to 90°C (194°F) in dry conditions.
• W signifies suitability for wet conditions, and dash-2 (-2) marks that it can tolerate high temperatures even in wet environments.

For instance:

• THHN: Common in residential wiring, thermoplastic, heat-resistant for up to 75°C in dry environments.
• THWN-2: A more robust insulation for wet environments, resistant to 90°C, suitable for indoor and outdoor applications.

Specialty insulations like UF (Underground Feeder) and SE (Service Entrance) are used in specific conditions, such as underground or sunlight-exposed installations.

4. Types of Cables for Different Applications

Various types of cables exist, each designed for specific applications based on insulation, structure, and protective requirements:

Underground Feeder (UF-B) Cable

• UF-B cable is used for direct burial in the ground and must be buried at least 24 inches deep to avoid damage from tools or other ground disruptions.
• Encased in a thick, waterproof jacket, it protects internal conductors from moisture, chemicals, and physical wear. It is commonly used to extend power to outdoor locations such as sheds, lamp posts, or air conditioning units.
• The dash-B (-B) designation ensures that conductors can operate in temperatures up to 90°C (194°F).

Service Entrance (SE) Cable

• SE cable brings power from utility transformers into buildings, connecting from the service drop to the meter and the main panel.
• Rated for outdoor and sunlight-exposed installations, it cannot be buried, as it is designed solely for above-ground applications.
• SE cables often contain aluminum conductors to reduce cost, given that they are typically large and long. Variants include:
  • SER (round): Includes multiple conductors with a bare neutral.
  • SEU (flat): Contains fewer conductors, often for applications requiring a simple layout.

5. Metallic Cables: Armored (AC) vs. Metal-Clad (MC)

Armored (AC) and Metal-Clad (MC) cables provide additional protection with a metallic outer armor, although they differ in several critical features.

Armored Cable (AC)

• AC, also known as BX, has a flexible metal armor that serves as the grounding conductor through its jacket and a bonding wire inside.
• Suitable only for dry indoor environments, AC cannot be used in outdoor, wet, or high-heat conditions. Additionally, its metal armor is more delicate than regular conduit and requires protection in potentially damaging environments.
• Typically used for residential wiring, where the ground can be connected directly to the armor.

Metal-Clad Cable (MC)

• MC cable is more versatile, designed for indoor, outdoor, and even underground installations if rated by the manufacturer. Unlike AC, MC cables are available in a wide variety of conditions and locations.
• MC has a dedicated insulated grounding wire inside, rather than using the metal armor as the ground. This allows the cable to function as an independent ground path, meeting broader code requirements.
• It is compatible with wet conditions and can have a plastic jacket around the armor for enhanced protection in damp environments.

6. Multiconductor Cables

Multiconductor cables bundle two or more conductors into one jacket, simplifying installation and improving safety by keeping different circuits separate. A few common types include:

• NM-B (Non-Metallic) or Romex: Primarily used in residential applications, NM-B cables feature a thermoplastic jacket with insulated conductors for indoor dry applications. They come in different color-coded jackets to identify wire gauge.
• Underground Feeder (UF-B): Designed for direct burial, UF-B features a thick, waterproof jacket, making it suitable for wet and corrosive environments.
• Service Entrance (SE): Used to bring utility power to buildings, SE is rated for outdoor, above-ground use and can withstand direct sunlight.