# 30 Amp Wire Size: What Wire Size Is Needed For A 30 Amp Breaker

Properly dimensioning wires for 30 Amps currents is vital when powering high-power tools, appliances, and devices, but also 30 Amps RVs, and similar loads.

Properly calculated wires transfer power without excess energy losses and without heating too much. Having thicker wires can help, but it is not always feasible to just put very thick wires and to hope for the best.

Updated: August 23, 2023.

## AWG Wire Size Chart: Calculate 30 Amp Wire Size

When trying to calculate proper wire thickness for 30 Amps current, it is necessary to check the Ampacity (current load carrying ability) of the wires in relation to the wire thickness and the maximum allowed temperature.

The following AWG wire size chart lists some of the most common wire thicknesses with wire Ampacities:

 AWG# Diameter(mm/inches) Area(mm2/in2) Resistance (Copper)(mΩ/m;mΩ/ft) Ampacity (A) @60°C/140°F @75°C/167°F @90°C/194°F 4/0(0000) 11.68400.4600 107.21930.1662 0.16080.04901 195 230 260 3/0(000) 10.40490.4096 85.02880.1318 0.20280.06180 165 200 225 2/0(00) 9.26580.3648 67.43090.1045 0.25570.07793 145 175 195 AWG 0 (1/0) 8.25150.3249 53.47510.0829 0.32240.09827 125 150 170 1 7.34810.2893 42.40770.0657 0.40660.1239 110 130 145 2 6.54370.2576 33.63080.0521 0.51270.1563 95 115 130 3 5.82730.2294 26.67050.0413 0.64650.1970 85 100 115 AWG 4 5.18940.2043 21.15060.0328 0.81520.2485 70 85 95 5 4.62130.1819 16.77320.0260 1.0280.3133 - - - AWG 6 4.11540.1620 13.30180.0206 1.2960.3951 55 65 75 7 3.66490.1443 10.54880.0164 1.6340.4982 - - - AWG 8 3.26360.1285 8.36560.0130 2.0610.6282 40 50 55 9 2.90640.1144 6.63420.0103 2.5990.7921 - - - AWG 10 2.58820.1019 5.26120.0082 3.2770.9989 30 35 40 11 2.30480.0907 4.17230.0065 4.1321.260 - - - AWG 12 2.05250.0808 3.30880.0051 5.2111.588 20 25 30 13 1.82780.0720 2.62400.0041 6.5712.003 - - - AWG 14 1.62770.0641 2.08090.0032 8.2862.525 15 20 25 15 1.44950.0571 1.65020.0026 10.453.184 - - - 16 1.29080.0508 1.30870.0020 13.174.016 - - 18 17 1.14950.0453 1.03780.0016 16.615.064 - - - AWG 18 1.02370.0403 0.82300.0013 20.956.385 10 14 16 19 0.91160.0359 0.65270.0010 26.428.051 - - - 20 0.81180.0320 0.51760.0008 33.3110.15 5 11 - 21 0.72290.0285 0.41050.0006 42.0012.80 - - - 22 0.64380.0253 0.32550.0005 52.9616.14 3 7 - 23 0.57330.0226 0.25820.0004 66.7920.36 - - - 24 0.51060.0201 0.20470.0003 84.2225.67 2.1 3.5 - 25 0.45470.0179 0.16240.0003 106.232.37 - - - 26 0.40490.0159 0.12880.0002 133.940.81 1.3 2.2 - 27 0.36060.0142 0.10210.0002 168.951.47 - - - 28 0.32110.0126 0.08100.0001 212.964.90 0.83 1.4 - 29 0.28590.0113 0.06420.0001 268.581.84 - - - 30 0.25460.0100 0.05090.0001 338.6103.2 0.52 0.86 - 31 0.22680.0089 0.04040.0001 426.9130.1 - - - 32 0.20190.0080 0.03200.0000 538.3164.1 0.32 0.53 - 33 0.17980.0071 0.02540.0000 678.8206.9 - - - 34 0.16010.0063 0.02010.0000 856.0260.9 0.18 0.3 - 35 0.14260.0056 0.01600.0000 1079329.0 - - - 36 0.12700.0050 0.01270.0000 1361414.8 - - - 37 0.11310.0045 0.01000.0000 1716523.1 - - - 38 0.10070.0040 0.00800.0000 2164659.6 - - - 39 0.08970.0035 0.00630.0000 2729831.8 - - - 40 0.07990.0031 0.00500.0000 34411049 - - -

Note: Ampacities are given for enclosed wires @86°F (@30°C) ambient temperatures.

When calculating the required wire thickness, it is necessary to apply a few additional rules in order to keep the wire surface temperatures at the maximum levels and to keep energy losses to the required minimum.

For example, if we check the default Ampacity values in the chart, we can find out the Ampacity of 30 Amps of the following wires:

• @60°C/140°F: AWG 10 - 30 Amps,
• @75°C/167°F: AWG 10 - 35 Amps,
• @90°C/194°F: AWG 12 - 30 Amps.

Note: if we can't find the exact Ampacity for a certain wire at the required temperature, we must choose the next larger one. And these are default values.

### 80% Rule

In order to increase safety and keep energy losses in check, the 80% Rule is applied. That means that we are not looking for a wire that features an Ampacity of 30 Amps, but for:

Ampacity = 30 Amps / 0.8 = 37.5 Amps

And if we check the Ampacity values in the chart, we get:

• @60°C/140°F: AWG 8 - 40 Amps,
• @75°C/167°F: AWG 8 - 50 Amps,
• @90°C/194°F: AWG 10 - 40 Amps.

As one can see, as soon as the 80% Rule is applied, actual wire thickness increases from AWG 10 (30 Amps) to AWG 8 (40 Amps) for 60°C/140°F.

And these values are only for relatively short wires. For very long wires, one must also calculate energy losses due to the wire length.

### Longer Wires - 10% per 50 Feet

When longer wires are used, in order to find the wire that can support 30 Amps current, the required Ampacity increases by 10% for every 50 feet (~15m) of the wire length.

For example, when calculating the required Ampacity for the 50 feet, 100 feet, and 150 feet wires, we can use (the default value is 37.5 Amps, after applying the "80% Rule"):

50 feet wire: Ampacity = 37.5 Amps * 1.1 = 41.25 Amps

100 feet wire: Ampacity = 37.5 Amps * 1.2 = 45 Amps

150 feet wire: Ampacity = 37.5 Amps * 1.3 = 48.75 Amps

Now, we have to check the required AWG value for given wire lengths, depending on the wire surface temperature - values are given in the following chart:

 Wire Length / Surface Temperature @60°C/140°F 75°C/167°F 90°C/194°F <50 feet (37.5 Amps) AWG 8 (40 Amps) AWG 8 (50 Amps) AWG 10 (40 Amps) 50 feet (41.25 Amps) AWG 6 (55 Amps) AWG 8 (50 Amps) AWG 8 (55 Amps) 100 feet (45 Amps) AWG 6 (55 Amps) AWG 8 (50 Amps) AWG 8 (55 Amps) 150 feet (48.75 Amps) AWG 6 (55 Amps) AWG 8 (50 Amps) AWG 8 (55 Amps)

Note: the actual surface temperatures due to the current flowing through the wires will be lower, but to keep calculations simpler, maximum allowed currents are calculated using these formulas - remember that the actual goal is to keep energy losses low in longer cables AND to keep their maximum surface temperatures at the certain level.

Also, note that these are values for enclosed copper wires - other wire thicknesses are required if the wires are made of aluminum or suspended in the air.

## 30 Amp Wire Size - Wires Suspended In Air

When the wires are suspended in air, for example, you use an extension cord to connect your 30 Amp RV to shore power, somewhat thinner wires may be used due to better cooling.

However, also keep in mind that these wires are often exposed to the sun, which can increase their surface temperature above 60°C/140°F even when the wires are disconnected from a power source.

If we check the Ampacities of Wires in the Free Air chart for copper and aluminum:

 Wire Size(AWG or kcmil) Ampacity (Copper Wire) Ampacity (Aluminum Wire) 60°C(140°F) 75°C(167°F) 90°C(194°F) 60°C(140°F) 75°C(167°F) 90°C(194°F) AWG 14 Wire 25 30 35 – – – AWG 12 Wire 30 35 40 25 30 35 AWG 10 Wire 40 50 55 35 40 40 AWG 8 Wire 60 70 80 45 55 60 AWG 6 Wire 80 95 105 60 75 80 AWG 4 Wire 105 125 140 80 100 110 3 120 145 165 95 115 130 2 140 170 190 110 135 150 1 165 195 220 130 155 175 AWG 1/0 Wire 195 230 260 150 180 205 2/0 225 265 300 175 210 235 3/0 260 310 350 200 240 275 4/0 300 360 405 235 280 315 250 340 405 455 265 315 355 300 375 445 505 290 350 395 350 420 505 570 330 395 445 400 kcmil Wire 455 545 615 355 425 480 500 kcmil Wire 515 620 700 405 485 545 600 575 690 780 455 540 615 700 630 755 855 500 595 675 750 655 785 885 515 620 700 800 680 815 920 535 645 725 900 730 870 985 580 700 785 1000 780 935 1055 625 750 845 1250 890 1065 1200 710 855 960 1500 980 1175 1325 795 950 1075 1750 1070 1280 1445 875 1050 1185 2000 1155 1385 1560 960 1150 1335

Types:

• 60°C (140°F): TW, UF,
• 75°C (167°F): RHW, THHW, THW, THWN, XHHW, ZW,
• 90°C (194°F): FEP, FEPB, MI, RHH, RHW-2, SA, SIS, TBS, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2.

We can see the default Ampacities for copper:

• @60°C/140°F: AWG 12 - 30 Amps,
• @75°C/167°F: AWG 14 - 30 Amps,
• @90°C/194°F: AWG 14 - 35 Amps.

And for aluminum:

• @60°C/140°F: AWG 10 - 35 Amps,
• @75°C/167°F: AWG 12 - 30 Amps,
• @90°C/194°F: AWG 12 - 35 Amps.

### 80% Rule

80% Rule is a very important safety rule - thus, for 30 Amp wire suspended in air, we are looking for a wire that can withstand 37.5 Amps:

For copper:

• @60°C/140°F: AWG 10 - 40 Amps,
• @75°C/167°F: AWG 10 - 50 Amps,
• @90°C/194°F: AWG 12 - 40 Amps.

And for aluminum:

• @60°C/140°F: AWG 8 - 45 Amps,
• @75°C/167°F: AWG 10 - 40 Amps,
• @90°C/194°F: AWG 10 - 40 Amps.

Similarly, one can calculate the correct wire size for longer copper and aluminum wires suspended in the air using the 50ft/10% rule.

Personally, thicker wires are harder to work with, they are heavier and more expensive, but in the long run, they have lower energy losses, and generally, they are safer.

## 30 Amps Electric Breaker Wire

When connecting 30 Amps electric breakers, generally, one uses relatively short wires, well shorter than 50 feet.

Thus, in most situations, using 8-gauge wires for connecting 30 Amps electric breakers is safe.

However, if the wires are going to be longer than 30-40 feet and especially if they are going to be heavily loaded (25-30 Amps almost constantly), consider using 6-gauge wires for additional safety and for reducing energy losses in the wires.

## What Size Wire Is Needed for a 30 Amp RV Plug?

30 Amp RV receptacle/outlet is used for powering 30 Amp RVs either using mains/shore power or 30 Amp RV power generator.

In order to transfer power without too much energy losses, it is recommended to use thick enough wire.

If we check one of the previous charts, for wires that are well below 50 feet (for safety reasons, we will use charts for enclosed/insulated wires), it is recommended to use 8-gauge copper wire, and for 50 feet, 100 feet, and 150 feet wires, it is recommended to use 6-gauge copper wire.

Many RV enthusiasts consider AWG 10 to be thick enough for 30 Amps RV cables, and in most situations, such wires are thick enough since RVs don't draw 30 Amps all the time. But, at the moment when RVs start to draw currents in the 25-30 Amps range, 10-gauge wire will start to get rather warm, even if it is suspended in the air.

Here are some of the most common Frequently Asked Questions (FAQ) about 30 Amp wires, breakers, etc.

### Can a 12/2 Wire Carry 30 Amps?

A 12-gauge wire, sometimes written as 12/2 wire, is not suitable for 30 Amps service.

The default Ampacity of 12-gauge wire is 20 Amps @60°C/140°F for enclosed/insulated wire and 30 Amps @60°C/140°F for copper wire suspended in air.

80% Rule is a very important rule, thus, be aware that we are not looking for a wire that can transfer 30A safely but 37.5A.

For short, 12-gauge wire is not suitable for 30 Amps service.

### How many Amps will 12/2 wire carry?

12/2 or 12-gauge wire can carry 20 Amps by default.

However, after applying the 80% Rule, 16 Amps is the maximum recommended current for enclosed/insulated copper wire for shorter distances.

For longer distances, after applying the 80% Rule, also apply the 50ft/10% rule.

### Is RV service 110V or 220V?

30 Amps RV service is AC 110V, which is compatible with US electrical systems found at homes and offices.

50 Amps RV service may be both 110V and 220V - it may have four wires, one ground, one neutral, and two live wires, which are 110V when measured from neutral and 220V when measured between them.

### How far can 10-gauge wire carry 30 amps?

To avoid overheating, 10-gauge enclosed/insulated copper wire generally should not be used for 30 Amps. Instead, use an 8-gauge wire.

For copper wires suspended in air, a 10-gauge wire can be used for shorter distances.

Note: If unsure, always check your local building codes to find out specific wire gauge requirements for your area.

Long Story Short: when calculating 30 Amps wire size, it is not enough just to check default Ampacity values without considering safety margin and wire length.

And that is why some people recommend even 10-gauge wire for 30 Amps RV cables - such cables can withstand such currents for some time, but with the risk of higher wire temperatures and increased energy losses.

If unsure what to do, always check the manual of your RV and contact local certified electrician regarding wire thickness, local laws, safety margins and similar - whatever You do, stay safe ...