What Size of Gauge Wire Should You Use for a 30 Amp Breaker?

A burned wire when you inspect your circuit breaker is a surprise that you do not want to get. Fortunately, this is an avoidable scenario if you know that having the right size of the gauge wire for a circuit breaker is important. The bad news is, this is something that a lot of people; they mistakenly believe that one wire is as good as any other so they attempt to make the connections themselves instead of calling for an electrician.

Anything involving breakers, such as its connections, should be taken seriously because it has to do with electricity. If you have the right components installed, you will avoid any known electric hazards and issues common to circuit breakers and faulty connections. In fact, many of these issues occur because of the wrong sized wire gauges used for the breakers. This is why it is important to know the right combination of the breaker and its compatible wire gauge sizes.

If you have a 30 amp breaker right for your air conditioner, water heater, or clothes dryer that needs to be wired but you are clueless about what size of the wire gauge is needed, allow us to help you out with not just that but also in understanding the basics involving wire gauges.

What Happens if You Use Too Small Gauge Wire?

People believe that as long as both ends of a certain wire will fit a connector, they can use it for their connections with no issue. Unfortunately, this is not the case for breakers. Those who are unaware of its importance often use too small gauge wires to connect their breakers, often because they want to save money since smaller wire gauges are cheaper.

Sadly, this only leads to costly mistakes for them.

If you use larger wires on your breaker, the only effect it will have is on your budget. This is because you ended up spending more than what you need to since larger wires cause more. It does not have an effect on your breaker nor will it cause damage to it, as it can handle the current that flows through it.

But if you use a wire gauge that is too small for your breaker, the following can happen:

  • Melted Wires – the smaller the wire, the less amount of current it can handle and the higher its resistance to the flow of energy. But if the wire gauge is too small for your breaker, the current that flows through the wire is more than what it is designed to handle. Since the wire has a high resistance, heat is generated and this will eventually be enough to melt the wires.
  • Performance Drops – any appliance or equipment that is connected to the circuit with the too-small gauge wire will not operate at peak efficiency. This is because it receives only a fraction of the energy it requires to run at full performance.
  • May Damage Equipment – aside from affecting its performance, using a smaller wire gauge can eventually damage your equipment. Power being supplied improperly can cause them to go bust
  • Can Start Fires – this is the worst that can happen when a wire gauge is too small to handle the current it receives. While circuit breakers have their own safety measures, such as tripping when it experiences an overload, this may not be enough to prevent a fire because of the wrong wire gauge used

These scenarios are totally avoidable, as long as you use the right wire gauge for a circuit breaker.

Wire Gauge Size Chart

While electrical work should ideally be handled by licensed electricians, it also helps to be personally aware of important aspects of your circuit breaker, such as the suitable wire gauge. To select the right wire gauge, professionals use different wire gauge size charts as their reference.

In the USA, the wire gauge size chart that is considered standard is the American Wire Gauge, commonly referred to as AWG. Also known as the Brown & Sharpe wire gauge, the AWG is a system that prescribes specific sizes or diameters of solid round wires, referred to as the wire gauge, to be used as electric conductors. The ampacity, or amperage capacity, is the maximum current that the wire gauges can handle.

What you should note is that the AWG numbering system does not directly represent the actual size of the wire. This means the higher the AWG number, the thinner or smaller the size of the wire and the smaller its ampacity. This is why a 2-gauge wire can carry a higher ampacity than a 14-gauge wire.

To better understand it, you can use the following chart to determine the diameter of a wire in inches and millimeters in terms of the AWG number:

AWG Diameter (inches) Diameter (millimeters)
0000 0.46 11.68
000 0.4096 10.4
00 0.3648 9.266
0 0.3249 8.251
1 0.2893 7.348
2 0.2576 6.544
3 0.2294 5.827
4 0.2043 5.189
5 0.1819 4.621
6 0.162 4.115
7 0.1443 3.665
8 0.1285 3.264
9 0.1144 2.906
10 0.1019 2.588
11 0.09074 2.305
12 0.08081 2.053
13 0.07196 1.828
14 0.06408 1.628
15 0.05707 1.45
16 0.05082 1.291
17 0.04526 1.149
18 0.0403 1.024
19 0.03589 0.9116
20 0.03196 0.8118
21 0.02846 0.7229
22 0.02535 0.6438
23 0.02257 0.5733
24 0.0201 0.5106
25 0.0179 0.4547
26 0.01594 0.4049
27 0.0142 0.3606
28 0.01264 0.3211
29 0.01126 0.2859
30 0.01002 0.2546
31 0.00893 0.2268
32 0.00795 0.2019
33 0.00708 0.1798
34 0.00631 0.1601
35 0.00562 0.1426
36 0.005 0.127
37 0.00445 0.1131
38 0.00397 0.1007
39 0.00353 0.08969
40 0.00314 0.07986

As you can see, the largest wire gauge in terms of diameter is 0000-gauge, while the smallest is 40-gauge. This means the 0000-wire gauge has a bigger ampacity than a 40-gauge wire, and this also means that the 0000-wire gauge allows more energy to flow through it.

Wire Gauge and Circuit Breaker

Now that you have a better understanding of the relationship between ampacity and the wire gauge, it is time to determine what wire gauge is suitable for specific circuit breakers.

If you have no idea where to find the amperage of your circuit breaker, look for the number on the handle of the breaker itself; this number is the maximum amperage of that breaker.

Once you find the amperage of your breaker, you can now determine what wire gauge to use. The most common wire gauge and their corresponding ampacity are:

Wire Gauge (AWG Number) Ampacity
14 15
12 20
10 30
8 40
6 55
4 70
3 85
2 95

The chart above is for copper wires with an ambient temperature rating of 60 ℃ or 140 ℉, which is considered as the standard. But in some cases, the suitable wire gauge for a specific ampacity will change depending on the wire used and the ambient temperature rating.

Copper is known to carry more ampacity than aluminum, that is why at the same wire gauge, it can handle more compared to its aluminum counterpart. This means if you have a 6-gauge copper wire and a 6-gauge aluminum wire, the copper wire will allow more current to flow through it.

Not only that, but wire gauges with a higher ambient temperature rating can be used at higher ampacity. This is why a 14-gauge copper wire with a 60 ℃ or 140 ℉ ambient temperature rating is suitable for a 15 amp breaker, while the same wire gauge but with an ambient temperature rating of 90 ℃ or 194 ℉ can be safely used with a 25 amp breaker.

These factors are what makes choosing the size of gauge wire to use for a 30 amp breaker not as straightforward as it seems. From the chart above, a 10-gauge copper wire with an ambient temperature rating of 60 ℃ or 140 ℉ is seen as standard in most conditions. However, you can also use a 10-gauge aluminum wire with a 90 ℃ or 194 ℉ ambient temperature rating, as well as wire gauges larger than these two sizes.

Always remember that it is fine to get a wire gauze bigger than the recommended size for a circuit breaker, but you should never use a gauge wire that is smaller for the available ampacity of the breaker.

How Many Amps Can a 12-Gauge Wire Handle?

The amps that a 12-gauge wire can handle are:

  • 20 for a copper wire with an ambient temperature rating of 60 ℃ or 140 ℉, which is the most common connection
  • 25 for a copper wire with an ambient temperature rating of 75 ℃ or 167 ℉
  • 30 for a copper wire with an ambient temperature rating of 90 ℃ or 194 ℉
  • 20 for an aluminum wire with an ambient temperature rating of 75 ℃ or 167 ℉
  • 30 for an aluminum wire with an ambient temperature rating of 90 ℃ or 194 ℉

Can a 10-Gauge Wire Handle 35 Amps?

Say you have a 35 amps breaker and a 10-gauge wire lying around. You may be wondering if this particular wire can handle that much current. It is possible but it will depend on the type of wire and its ambient rating.

Only a 10-gauge copper wire with either a 75 ℃ or 167 ℉ or 90 ℃ or 194 ℉ ambient temperature rating, as well as a 10-gauge aluminum wire with an ambient temperature rating of 90 ℃ or 194 ℉ can handle 35 Amps.

Can a 12-Gauge Wire Handle 25 Amps?

If you are wondering if your extra 12-gauge wire can also be used for a 25 amp breaker, it is possible to do so. A 12-gauge copper wire can be used if its ambient temperature rating is either 75 ℃ or 167 ℉ or 90 ℃ or 194 ℉, while a 12-gauge aluminum wire is compatible if its ambient temperature rating is 90 ℃ or 194 ℉.

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