Battery Equivalents and Replacements

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.

Published: May 6, 2022.

30 amp wire size 1

AWG Wire Size Chart

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)
Diameter
(inches)
Area
(mm2)
Area
(in2)
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 195 230 260
3/0
(000)
10.4049 0.4096 85.0288 0.1318 165 200 225
2/0
(00)
9.2658 0.3648 67.4309 0.1045 145 175 195
0 8.2515 0.3249 53.4751 0.0829 125 150 170
1 7.3481 0.2893 42.4077 0.0657 110 130 145
2 6.5437 0.2576 33.6308 0.0521 95 115 130
3 5.8273 0.2294 26.6705 0.0413 85 100 115
4 5.1894 0.2043 21.1506 0.0328 70 85 95
5 4.6213 0.1819 16.7732 0.0260 - - -
6 4.1154 0.1620 13.3018 0.0206 55 65 75
7 3.6649 0.1443 10.5488 0.0164 - - -
8 3.2636 0.1285 8.3656 0.0130 40 50 55
9 2.9064 0.1144 6.6342 0.0103 - - -
AWG 10 2.5882 0.1019 5.2612 0.0082 30 35 40
11 2.3048 0.0907 4.1723 0.0065 - - -
12 2.0525 0.0808 3.3088 0.0051 20 25 30
13 1.8278 0.0720 2.6240 0.0041 - - -
AWG 14 1.6277 0.0641 2.0809 0.0032 15 20 25
15 1.4495 0.0571 1.6502 0.0026 - - -
16 1.2908 0.0508 1.3087 0.0020 - - 18
17 1.1495 0.0453 1.0378 0.0016 - - -
18 1.0237 0.0403 0.8230 0.0013 10 14 16
19 0.9116 0.0359 0.6527 0.0010 - - -
20 0.8118 0.0320 0.5176 0.0008 5 11 -
21 0.7229 0.0285 0.4105 0.0006 - - -
22 0.6438 0.0253 0.3255 0.0005 3 7 -
23 0.5733 0.0226 0.2582 0.0004 - - -
24 0.5106 0.0201 0.2047 0.0003 2.1 3.5 -
25 0.4547 0.0179 0.1624 0.0003 - - -
26 0.4049 0.0159 0.1288 0.0002 1.3 2.2 -
27 0.3606 0.0142 0.1021 0.0002 - - -
28 0.3211 0.0126 0.0810 0.0001 0.83 1.4 -
29 0.2859 0.0113 0.0642 0.0001 - - -
30 0.2546 0.0100 0.0509 0.0001 0.52 0.86 -
31 0.2268 0.0089 0.0404 0.0001 - - -
32 0.2019 0.0080 0.0320 0.0000 0.32 0.53 -
33 0.1798 0.0071 0.0254 0.0000 - - -
34 0.1601 0.0063 0.0201 0.0000 0.18 0.3 -
35 0.1426 0.0056 0.0160 0.0000 - - -
36 0.1270 0.0050 0.0127 0.0000 - - -
37 0.1131 0.0045 0.0100 0.0000 - - -
38 0.1007 0.0040 0.0080 0.0000 - - -
39 0.0897 0.0035 0.0063 0.0000 - - -
40 0.0799 0.0031 0.0050 0.0000 - - -

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 minumum.

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 to keep the 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 the 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 (default value is 37.5 Amp, 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.

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, it is safe to use 8 gauge wires for connecting 30 Amps electric breakers.

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 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 the previous chart, for wires that are well below 50 feet, it is recommended to use 8 gauge wire, and for 50 feet, 100 feet, and 150 feet wires, it is recommended to use 6 gauge 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...

6 awg wire


Long Story Short: when calculating 30 Amps wire size, it is not enough just to check default Ampacity values, without taking into account 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 ...