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 highpower 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 (mm^{2}/in^{2}) 
Resistance (Copper) (mΩ/m;mΩ/ft) 
Ampacity (A)  
@60°C/140°F  @75°C/167°F  @90°C/194°F  
4/0 (0000) 
11.6840 0.4600 
107.2193 0.1662 
0.1608 0.04901 
195  230  260 
3/0 (000) 
10.4049 0.4096 
85.0288 0.1318 
0.2028 0.06180 
165  200  225 
2/0 (00) 
9.2658 0.3648 
67.4309 0.1045 
0.2557 0.07793 
145  175  195 
AWG 0 (1/0)  8.2515 0.3249 
53.4751 0.0829 
0.3224 0.09827 
125  150  170 
1  7.3481 0.2893 
42.4077 0.0657 
0.4066 0.1239 
110  130  145 
2  6.5437 0.2576 
33.6308 0.0521 
0.5127 0.1563 
95  115  130 
3  5.8273 0.2294 
26.6705 0.0413 
0.6465 0.1970 
85  100  115 
AWG 4  5.1894 0.2043 
21.1506 0.0328 
0.8152 0.2485 
70  85  95 
5  4.6213 0.1819 
16.7732 0.0260 
1.028 0.3133 
     
AWG 6  4.1154 0.1620 
13.3018 0.0206 
1.296 0.3951 
55  65  75 
7  3.6649 0.1443 
10.5488 0.0164 
1.634 0.4982 
     
AWG 8  3.2636 0.1285 
8.3656 0.0130 
2.061 0.6282 
40  50  55 
9  2.9064 0.1144 
6.6342 0.0103 
2.599 0.7921 
     
AWG 10  2.5882 0.1019 
5.2612 0.0082 
3.277 0.9989 
30  35  40 
11  2.3048 0.0907 
4.1723 0.0065 
4.132 1.260 
     
AWG 12  2.0525 0.0808 
3.3088 0.0051 
5.211 1.588 
20  25  30 
13  1.8278 0.0720 
2.6240 0.0041 
6.571 2.003 
     
AWG 14  1.6277 0.0641 
2.0809 0.0032 
8.286 2.525 
15  20  25 
15  1.4495 0.0571 
1.6502 0.0026 
10.45 3.184 
     
16  1.2908 0.0508 
1.3087 0.0020 
13.17 4.016 
    18 
17  1.1495 0.0453 
1.0378 0.0016 
16.61 5.064 
     
AWG 18  1.0237 0.0403 
0.8230 0.0013 
20.95 6.385 
10  14  16 
19  0.9116 0.0359 
0.6527 0.0010 
26.42 8.051 
     
20  0.8118 0.0320 
0.5176 0.0008 
33.31 10.15 
5  11   
21  0.7229 0.0285 
0.4105 0.0006 
42.00 12.80 
     
22  0.6438 0.0253 
0.3255 0.0005 
52.96 16.14 
3  7   
23  0.5733 0.0226 
0.2582 0.0004 
66.79 20.36 
     
24  0.5106 0.0201 
0.2047 0.0003 
84.22 25.67 
2.1  3.5   
25  0.4547 0.0179 
0.1624 0.0003 
106.2 32.37 
     
26  0.4049 0.0159 
0.1288 0.0002 
133.9 40.81 
1.3  2.2   
27  0.3606 0.0142 
0.1021 0.0002 
168.9 51.47 
     
28  0.3211 0.0126 
0.0810 0.0001 
212.9 64.90 
0.83  1.4   
29  0.2859 0.0113 
0.0642 0.0001 
268.5 81.84 
     
30  0.2546 0.0100 
0.0509 0.0001 
338.6 103.2 
0.52  0.86   
31  0.2268 0.0089 
0.0404 0.0001 
426.9 130.1 
     
32  0.2019 0.0080 
0.0320 0.0000 
538.3 164.1 
0.32  0.53   
33  0.1798 0.0071 
0.0254 0.0000 
678.8 206.9 
     
34  0.1601 0.0063 
0.0201 0.0000 
856.0 260.9 
0.18  0.3   
35  0.1426 0.0056 
0.0160 0.0000 
1079 329.0 
     
36  0.1270 0.0050 
0.0127 0.0000 
1361 414.8 
     
37  0.1131 0.0045 
0.0100 0.0000 
1716 523.1 
     
38  0.1007 0.0040 
0.0080 0.0000 
2164 659.6 
     
39  0.0897 0.0035 
0.0063 0.0000 
2729 831.8 
     
40  0.0799 0.0031 
0.0050 0.0000 
3441 1049 
     
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, RHW2, SA, SIS, TBS, THHN, THHW, THW2, THWN2, USE2, XHH, XHHW, XHHW2, ZW2.
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 8gauge wires for connecting 30 Amps electric breakers is safe.
However, if the wires are going to be longer than 3040 feet and especially if they are going to be heavily loaded (2530 Amps almost constantly), consider using 6gauge 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 8gauge copper wire, and for 50 feet, 100 feet, and 150 feet wires, it is recommended to use 6gauge 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 2530 Amps range, 10gauge wire will start to get rather warm, even if it is suspended in the air.
Frequently Asked Questions (FAQ)
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 12gauge wire, sometimes written as 12/2 wire, is not suitable for 30 Amps service.
The default Ampacity of 12gauge 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, 12gauge wire is not suitable for 30 Amps service.
How many Amps will 12/2 wire carry?
12/2 or 12gauge 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 10gauge wire carry 30 amps?
To avoid overheating, 10gauge enclosed/insulated copper wire generally should not be used for 30 Amps. Instead, use an 8gauge wire.
For copper wires suspended in air, a 10gauge 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 10gauge 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 ...