Before you install the breaker, you must first select wiring of the correct size. The wrong wire size can destroy everything you own. In fact, unless you have experience in the electrical field, you should leave these decisions in the hands of a professional.
What Size Wire is Needed For A 30 Amps Breaker?
A 10-gauge wire can safely carry the current of a 30A breaker. The main objective is to ensure that the wire is large enough to match the breaker’s capacity. A small wire with an inadequate diameter will start a fire. This is why many professionals emphasize the minimum gauge for a 30A wire, but they don’t say anything about the maximum gauge.
Wire Size In Terms of Voltage
| Voltage | Wire Size |
| 110V | 10 Gauge |
| 120v | 10 Gauge |
| 220V | 10-2 copper wire |
| 230V | 10 Gauge |
| 240V | 10 Gauge |
| 3 Phase | 10 Gauge Copper Wire |
Wire Size In Terms of Pole
| Pole | Wire Size |
| Single Pole | 10 Gauge |
| 2 Pole | 10 Gauge |
You need a minimum of 10AWG. The gauge determines the size of a wire. A gauge is a number. The higher the number, the smaller the wire. The lower the number, the bigger the wire.
The maximum gauge doesn’t matter. The wire can be as large as you want. The use of a thicker wire does not attract any dangerous consequences. In some locations, the local authorities expect consumers to use wires ranging from 8AWG to 10AWG for 30A breakers. Many professionals agree with this assessment.
In that regard, you could argue that 10AWG is the minimum and 8AWG is the maximum.
What Does NEC Say About It?
NEC expects consumers to use 10-gauge wire for 30 amps regardless of whether the material is copper or aluminum.
| Current (amps) | Copper Wire (AWG) | Aluminum Wire (AWG) | NM Cable (AWG) |
| 15 | 14 | — | 14 |
| 20 | 12 | 12 | 12 |
| 30 | 10 | 10 | 10 |
| 40 | 8 | 8 | 8 |
| 50 | 8 | 6 | 8 |
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How Do I Determine The Correct Wire Size For 30 Amp Breaker?
To identify the correct wire size for a 30A breaker, you have to keep a few factors in mind, namely:
1). Lower AWG Is Better
As you now know, the gauge determines the size. In turn, the size of a wire tells you the amount of current the wire can safely carry. This is why the gauge is so important.
A 10-gauge wire carries more electricity than a 12-gauge wire. But it carries less electricity than an 8-gauge wire.
If you have a large breaker that can accommodate large volumes of electricity, you need an equally large wire.
2). SIze Of Wire Has To Match The Size Of The Breaker
The breaker protects the wires. If the wires carry more current than they can handle, the breaker will trip to prevent them from overheating. This is the reason why the size of the cables has to match the size of the breaker.
If the wire size is smaller than the breaker size, the wires will overheat and melt, and the breaker won’t respond because it has to detect more current than the small wire can carry to trip.
In other words, the current running through the circuit is high enough to cause overheating in the thin wires but too low to trip the breaker.
As such, if you want to change the breaker in your house, you must also change the wiring. A larger gauge isn’t a problem. The breaker can still respond to the current passing through a large wire before the wire overheats. But a smaller gauge will burn your house to the ground.
3). Don’t Use Thin Wires
People use small wires despite the dangers involved because they are cheap. Thicker wires have heftier price tags than their thinner counterparts. Contractors use thin cables all the time to save money.
Some homeowners grow complacent because their houses have thin wires, yet they haven’t observed any signs of overheating. In truth, wires with a small gauge do not always lead to disaster.
For instance, I do not want you to pair 30-amp breakers with 12-gauge wire. 12-gauge wire is too small to operate a 30A breaker safely. However, 12-gauge wire on a 30A breaker will not overheat if you limit the number of appliances using the circuit simultaneously.
A 30A breaker can run substantial appliances like central air conditioners. But if your 30A breaker is running lights and TV sets, these devices cannot overwhelm the 12-gauge wire.
That being said, this practice is still risky. If a visitor decides to connect multiple heavy-duty items to the circuit, the 12-gauge wire will overheat.
Use 12-gauge wire with 20A breakers, not 30A.
4). Large Wires Are Always Safe
Many electricians encourage consumers to use larger wires because they are safe. For instance, the minimum wire size for 30A breakers is 10AWG. But you can use 6AWG, which is thicker than 10AWG if you want. People use larger wires to leave room for expansion.
However, you are better off using 10AWG. Larger wires reduce heat buildup. Unfortunately, they are expensive and heavier, and bulkier, making them more challenging to install.
Do not assume that you can avoid overheating and melting by simply selecting the thickest wire on the market. The thickest wire is inconvenient.
5). Copper Is Better Than Aluminum
The material makes a difference. Copper carries more electricity than aluminum. A 10AWG copper wire is better than a 10AWG aluminum wire because it can transmit more current.
Looking at the table that Atlantic Inspiration posted, you can see that 10AWG aluminum wire can carry 30A at 167 degrees and 194 degrees F.
On the other hand, 10AWG copper wire can carry 35A and 40A at 167 degrees and 194 degrees F, respectively. If you have to choose between copper and aluminum, get copper.
6). Increase In Length Also Increases The Size
If you increase the length of a wire, you must also increase the size. Increasing the length raises the resistance and voltage drop. You must compensate for these elements by raising the gauge. This allows appliances to receive the current they need regardless of the resistance and voltage drop.
10-gauge wire can accommodate a 30-amp breaker until you reach 150 feet. At 150 feet or more, you should get 8AWG or 6AWG wire.
7). Wrong Size Can Damage Your Appliance
People think that overheating is the only consequence of using a small wire. But that isn’t true. If you use a 12, 14, or even 16AWG wire on a 30A breaker, the performance of your appliances will drop. This is because the wires cannot transmit electricity in the quantities that your devices require.
Small wires can also damage your appliances because you keep forcing them to work even though they don’t have enough power. The motors in refrigerators can burn out.
8). Look At The Chart For Calculating The Right Wire Size
You don’t have to calculate the correct wire size for your breaker. Just use charts like the one on the Wolf Subzero Cove website. Most people use this approach. That includes professional electricians.
They all follow the same wiring standards and conventions. Those wiring standards and conventions clearly state that 30-amp breakers require 10AWG wire.
It is more important to calculate the size of the breaker. If you get the breaker size wrong, you could start a fire. People estimate the breaker size by adding the wattage of all their appliances together and dividing the total by the voltage of the power supply.
This gives you the amps. Multiply those amps by 1.25 to get the right amp rating for a breaker. Once you identify the amp rating of the breaker, you can use the NEC’s chart to find the wire size that matches that amp rating.
Does Distance Matter While Choosing A Wire?
The distance matters. A 10AWG wire can run a 30A breaker. However, if you increase the distance, the voltage drop will also increase. The appliance at the end of the wire won’t get the current it needs to operate optimally. If a 10AWG wire on a 30A breaker has to run more than 100 feet, jump to 8AWG
Some appliances will respond by drawing more electricity. This can lead to overheating. A thicker gauge solves this problem.
You should jump to the next gauge if your wire exceeds one hundred feet.
Can I Use 8 Gauge Wire On A 30 Amp Breaker?
You can see that 8-gauge wire usually works with 40A breakers. If an 8-gauge wire is large enough to run a 40A breaker, it is more than adequate for a 30A breaker. A wire can be too large, but it can’t be too small.
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