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:

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:

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:

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.

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 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 ...