Your home’s electrical system is like a circulatory system, with wires of various sizes, or gauges, carrying power where you need it. All these wire sizes may seem random, but the different wire gauges have distinct applications. The American Wire Gauge (AWG) system standardizes wire sizes, and understanding it can help you select the right wire for your projects.
In today’s video, Ask This Old House master electrician Heath Eastman teaches host Kevin O’Connor about wire gauges and shares the applications for different sizes of wires.
What Is American Wire Gauge (AWG)?
American Wire Gauge (AWG) is the standard system used in the U.S. to measure the diameter of electrical wires. In the AWG system, numbers represent wire sizes. The system might seem counterintuitive at first: the higher the gauge number, the thinner the wire. For example, a 14 AWG wire is thicker than an 18 AWG wire. This pattern continues until reaching 1 AWG.
For wires larger than 1 AWG, sizes are denoted using the term “aught” (pronounced “awt”). As the number of aughts increases, so does the wire’s thickness. There are four of these “zero” or “aught” gauges:
- 1/0 AWG (pronounced “one aught”)
- 2/0 AWG (pronounced “two aught”)
- 3/0 AWG (pronounced “three aught”)
- 4/0 AWG (pronounced “four aught”)
You’ll typically see these thicker, single-conductor cables in industrial settings and large residential applications, such as service entrance cables.
Why Different Wire Sizes Matter
Different wire gauges exist because different electrical applications require different amounts of power. Thicker wires can safely carry more electrical current than thinner wires, and they carry electricity more efficiently across long distances.
Electrical codes specify minimum wire sizes for various applications to ensure safety and performance. Using wire that’s too thin for a high-current application can cause overheating and potentially start a fire.
Wire size also affects voltage drop, which is the decrease in voltage that occurs as electricity travels through a wire. Using a thicker wire minimizes the resistance so that connected devices receive the right voltage.
Common Wire Sizes and Their Applications
Here’s a breakdown of some common wire gauges and their typical uses. Selecting the correct gauge ensures that your electrical system and everything connected to it operates efficiently and safely.
- 18 AWG: This is a thin wire commonly used for low-voltage applications such as doorbells, security systems, and thermostats.
- 14 AWG: This is the standard size for many residential applications, including 15-amp lighting circuits, bedroom and office outlets, and general-purpose household wiring.
- 12 AWG: This is a slightly thicker wire used for 20-amp circuits, kitchen and bathroom outlets, and other areas with devices that draw more current.
- 10 AWG: This thicker wire is suitable for 30-amp circuits, electric clothes dryers, small electric ovens, and window air conditioning units.
- 8 and 6 AWG: These wires are the largest you are likely to see inside your home. They’re used for high-current applications such as central air conditioning units, electric ranges, and electric vehicle charging stations.
- 4 AWG and beyond: These are very thick wires typically used for large industrial equipment, main service feeds, EV chargers, and subpanels.
Decoding Wire Labels and Conductor Counts
When shopping for electrical wires, you’ll often see designations like 14/2 or 12/3. These numbers provide important information about the wire’s characteristics, helping you choose the right type for your project.
The number before the slash indicates the wire gauge (AWG). The number after the slash represents the count of insulated conductors inside the wire jacket, excluding the ground wire. For example, a 14/2 wire contains two 14 AWG insulated conductors plus a ground wire, while a 12/3 wire contains three insulated 12 AWG conductors plus a ground wire.
The number of conductors you need depends on the specific electrical application. A 14/2 or 12/2 wire works for most standard household circuits. However, you would need a 14/3 or 12/3 wire for three-way switch circuits or other applications needing an additional conductor.
Choosing the Right Wire for Your Project
Selecting the appropriate wire size is key for safety and performance. Here are some factors to consider:
- Circuit amperage: The amperage rating of the circuit is a primary factor in wire selection. As a general rule, 15-amp circuits require 14 AWG wire, 20-amp circuits require 12 AWG wire, and 30-amp circuits require 10 AWG wire.
- Device power requirements: Consider the power needs of the devices you’ll connect to the circuit. High-power appliances like electric ovens or air conditioners may require thicker wires, even if the circuit amperage doesn’t demand it.
- Wire run length: Longer wire runs may require thicker wires to minimize voltage drop, especially for high-current applications. This consideration is especially important for large homes or setups with complex wiring paths.
- Environmental factors: Wire insulation varies, with different types designed to withstand specific environmental conditions such as moisture, heat, or chemical exposure. Select the right insulation for longevity and safety.
- Local electrical codes: Always consult and adhere to local electrical codes, which may have specific requirements for wire sizes in different applications.
Safety Considerations When Working With Wire Gauges
Working with electrical wiring can be dangerous. Here are some important safety tips:
- Always turn off the power at the main breaker before working on any electrical wiring.
- Use a voltage tester to confirm that wires are not live before handling them.
- Never exceed the ampacity rating of a wire.
- Keep your work area dry and clean to avoid hazards.
- Use appropriate personal protective equipment, such as insulated gloves and safety glasses.
- If you’re unsure about any aspect of electrical work, consult a licensed electrician.
When in doubt, it’s always best to consult with a professional electrician to guarantee your electrical system is safe and up to code.