Whether you’re installing, extending, or rewiring a circuit, finding out the wire gauge and amperage you will need is a key first step. The gauge—or size—of the wire used needs to match the circuit’s amperage rating (energy level). The higher the amperage rating, the larger the electrical wires need to be to avoid generating excess heat that can cause melted wires and even electrical fires.
Knowing how much energy your new lighting fixture, appliance, or heater will need, the type of wire your home currently uses when rewiring, and using an electrical wire size chart to ensure you have the right materials will all ensure your electrical project goes safely and smoothly, both in the short and long term.
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What Are Wire Gauges?
A wire gauge is the measurement of the diameter or thickness of a wire. The gauge determines how much electricity the wire can safely carry for different electrical applications.
The American Wire Gauge (AWG) system determines the standard gauge sizes. A higher wire gauge number means the wire is thinner. A lower wire gauge number means the wire is thicker and can carry more electrical current for longer distances than a thinner gauge.
Wire Gauge Conversion Chart
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A wire gauge chart helps you determine the wire gauge that matches the amps you need for the project. When purchasing wire, you’ll see a few different numbers on the packaging or product description.
- The number followed by AWG (American Wire Gauge) is the gauge of the entire wire. This number takes into account any smaller wires woven together within the insulation. Any numbers after AWG indicate how many strands of smaller wire are used, and the gauge of each.
- If a spool of wire is only labeled with a set of numbers (for example, 10/3), three separate 10-gauge strands within the wire can be used for connecting, plus a grounding wire.
- If you’re buying wires by size in inches or millimeters or have stripped and measured uninsulated wires with a gauge tool, use the wire gauge chart to determine the maximum amperage of a wire. Most charts provide ampacity for copper and aluminum wire and their most common insulation materials.
Wire Amperage Chart
| Wire Use | Rated Ampacity | Wire Gauge |
|---|---|---|
| Low-voltage lighting and lamp cords | 10 amps | 18-gauge |
| Extension cords (light-duty) | 13 amps | 16-gauge |
| Light fixtures, lamps, and lighting circuits | 15 amps | 14-gauge |
| Kitchen, bathroom, and outdoor receptacles (outlets); 120-volt air conditioners | 20 amps | 12-gauge |
| Electric clothes dryers, 240-volt window air conditioners, electric water heaters, sometimes cooktops, and wall ovens | 30 amps | 10-gauge |
| Cooktops and ranges | 40-50 amps | 6-gauge |
| Electric furnaces, large electric heaters | 60 amps | 4-gauge |
There’s a safety risk when a device or appliance tries to draw more power on a circuit than the wire gauge is rated for. Circuit breakers or wiring fuses offer protection against overloading and overheating, but they shouldn’t be your absolute go-to. Both are designed to sense current overloads and to trip or “blow” before the wires reach the danger point. However, nothing is foolproof, so it’s still important to stay below the amp rating by avoiding plugging too many appliances into a circuit.
Common Wire Sizes
| Amperage Capacities for Standard Non-Metallic (NM) Cable | |
|---|---|
| 16-gauge wire | 13 amps |
| 14-gauge wire | 15 amps |
| 12-gauge wire | 20 amps |
| 10-gauge wire | 30 amps |
| 8-gauge wire | 40 amps |
| 6-gauge wire | 55 amps |
| 4-gauge wire | 70 amps |
| 3-gauge wire | 85 amps |
| 2-gauge wire | 95 amps |
There are many types and sizes of electrical wire to choose from, and knowing the right wire size, or wire gauge, is the key to making the right choice for your needs. The smaller the wire gauge number, the larger the wire diameter. Common sizes include 16-, 14-, 12-, 10-, 8-, 6-, and 2-gauge wire. The size of the wire dictates how much current can safely pass through the wire.
Electrical current is measured in amps, and each wire gauge has a maximum safe carrying capacity. For standard non-metallic (NM) copper cable, these amperage and wire gauge capacities help you calculate what size wire you need.
Copper vs. Aluminum Wiring
Use the electrical wire size chart when working with copper wires. However, it’s important to know that aluminum wires may also be present in your space.
Aluminum wire was typically used for fixed wiring in the 1960s and ’70s to keep costs low when building homes. However, it also has a lower amperage capacity than copper; the wire needs to be thicker to carry the same current, and it tends to expand when it heats up, which can cause connection issues and fire safety concerns over time.
Although it’s more expensive than aluminum, copper wire is now the preferred material in homes, thanks to its strength, durability, and higher conductivity.
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Stranded vs. Solid Wire
It’s also important to purchase the style of wire that best fits your needs. Stranded wire is made up of multiple small strands woven together within insulation and tends to be more flexible, making it ideal for smaller areas. However, it’s also prone to fraying and more susceptible to damage.
Solid wire, on the other hand, is made of a single solid copper conductor. It tends to be much easier to secure in standard switches and receptacles and is best used for rewiring and installation projects needing a higher ampacity.
FAQ
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How can you tell which electrical wire size to use?
The size of the wire you’ll need to use should match the amp rating of the circuit. Use a wire amperage chart to determine the correct size wire.
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How many amps can a 12-gauge wire handle?
A 12-gauge wire is rated to handle up to 20 amps.
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What happens if you use a wire gauge that is too large?
A wire gauge that is too large isn’t necessarily dangerous, but it can carry too much current for the area.
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