3 Gauge Wire Amp Rating (Explained)

3 gauge wire amps

Laypeople don’t interact with this wire size because 3AWG is incredibly thick. The wires behind your sockets and lights are 12 to 14AWG, depending on the circuit size. You can run everything in your house on 12-gauge wiring.

When your circuit malfunctions, 12AWG is the thickest wire size you will encounter during repairs. 3AWG exceeds 12AWG’s thickness significantly. This is what you should know about the wire size:

Attributes of a 3AWG Wire

Laypeople use AWG to quantify a wire’s thickness. Contractors are the same. They use the gauge because you can interpret the unit of measurement quickly. But some engineers prefer inches, mm, and mm2 because of the precision they offer.

In the case of 3AWG, the wire size has a diameter of 0.229 inches (5.83mm) and a cross-sectional area of 26.7 mm2. You don’t have to calculate these figures. Tables like the one on The Engineering ToolBox will tell you the diameter and cross-sectional area of each wire size. This information comes from the NEC. Therefore, you can trust its accuracy.

How Many Amps Can 3 Gauge Wire Handle?

3-gauge wiring can safely transmit 85 amps. The ampacity shows you how much electricity a particular wire size can continuously transmit without overheating. It prevents fires by allowing you to pair each application with the correct wire size.

Once again, you don’t have to calculate a 3AWG line’s ampacity. The table below shows you the amps of each wire size. And again, this information fits the ampacities you see in the NEC’s tables.

Wire Gauge Size60˚C
3 AWG85 A100 A110 A65 A75 A85 A

Most regions in the United States adhere to the National Electric Code’s rules and regulations because their guidelines are accurate and reliable. Admittedly, local codes supersede the NEC. However, you will be hard-pressed to find a local code that disagrees with the idea that 3AWG wiring carries 85 amps.

You determine the ampacity by looking at the ‘Wire Gauge Size’ column in a wire size chart. Once you find 3AWG, check the corresponding row to see the ampacity at different temperature ratings.


How many odd-numbered wire sizes have you seen in your local store? Look at a wire size chart. Have you noticed that it only shows even-numbered gauges? The wire size jumps from 14 to 12, 10, 8, 6, and 4. But instead of skipping directly to 2, the wire size shows 3, 2, and even l.

That raises two questions. First, why do wire size charts skip odd numbers? Secondly, why does the wire size chart mention an odd-numbered gauge like 3AWG? The answer to the first question indirectly resolves the second one.

Wire size charts ignore odd-numbered gauges because the differences between odd and even-numbered gauges are too small to matter. Your retailer has no reason to stock 13AWG because you already have 14AWG and 12AWG.

14AWG is 0.064 inches. 12AWG (the next largest size) is 0.081 inches (copper). These two sizes are separated by a paltry 0.017 inches. In other words, any application that requires 13-gauge wiring can make do with 12AWG or even 14AWG.

So what sets 3AWG apart? The differences between even-numbered gauges are only minor among the smaller sizes. Those differences become more significant once you reach thicker wire sizes such as 3AWG.

Consider this. 4-gauge wiring is 0.204 inches. 2AWG wiring is 0.257 inches. The difference between these two sizes is 0.053. That is too significant for you to round up to 2AWG or down to 4AWG.

You need 3-gauge cabling whose 0.229 inches place the wire size in between 2AWG and 4AWG. This rationale applies to 1AWG.

Therefore, if your contractor asks for 3AWG, get them 3AWG. Don’t resort to the other wire sizes. Your local retailer won’t stock 5AWG, 7AWG, or 9AWG. But they should have a few coils of 3AWG wiring on hand because contractors use it.

Leave it up to your contractor to determine what they need. Don’t buy 3AWG to save money even though your contractor wanted 2AWG. At the same time, you shouldn’t waste money on 3AWG when 4AWG is sufficient.

Why Do People Call 3AWG THHN/THWN?

People don’t necessarily call this wire size THHN or THWN. However, BC Highlight Electric has noticed that consumers commonly associate 3 and 4AWG wiring with THHN and THWN. Or, at the very least, you typically find the wire sizes in the THHN category.

Telling a retailer you want number four wire is enough to get you THHN wiring. Contractors that want 2AWG may settle for 3AWG because the wire size is cheaper and lighter. THHN highlights the wire’s attributes (Thermoplastic High Heat Nylon). Initially, manufacturers sold 3AWG in THHN and THWN versions (the ‘W’ refers to the wire’s water resistance).

But the cost of selling two different types of wires was too high even though the differences were minor. Eventually, manufacturers combined the types. These days, your 3AWG wire will say ‘THHN THWN’ on the jacket.

These wires are fire and water-resistant. You can install them in wet and dry locations if you stay within the recommended temperature ratings.

Use of 3AWG

The lower you go on a wire size chart, the thicker the conductors become. In AWG, the smaller the number, the bigger the wire. In other words, 3AWG is quite large. The table below will give you an idea of what 3-gauge wiring will do in comparison to other wire sizes.

18AWGLamp Cords
16AWGExtension Cords
14AWGLights Fixtures
12AWGOutlets, Kitchen Appliances
10AWGDryers, Ovens, Air Conditioners, Heaters
8AWGCook Tops
6AWGLarge Furnaces and Heaters
4AWGLarge Furnaces and Heaters, Sub Panels
3AWGFeeder Wire and Service Entrance

3AWG and 4AWG have a lot in common. You can run heavy-duty appliances such as large water heaters and electric furnaces on a circuit with 3AWG cables. Additionally, you can use 4AWG as a feeder wire if the situation is ideal.

Does The Material Affect 3-Gauge Wiring Amps?

Yes, it does. Look at the wire size chart. The row at the top shows the materials. It limits your options to copper and aluminum because most retailers sell copper and aluminum wiring. From the table, you can see that a 3-gauge line’s ampacity changes with the material.

3AWG copper wires can transmit 85 to 110 amps. But 3AWG aluminum lines are restricted to 65 – 85 amps. Why? Because copper is more conductive than aluminum. Therefore, copper wiring has a higher ampacity than its aluminum counterpart.

What if you can’t afford copper? 3-gauge wiring is incredibly expensive. Adding copper to that mix makes things worse. What if your budget has forced you to prioritize aluminum? If your project requires 3AWG copper, get 2AWG aluminum. You can replace copper with aluminum if you raise the gauge.

Otherwise, an application that requires 3AWG copper may overwhelm 3AWG aluminum. Keep in mind that aluminum is lighter and easier to handle. In other words, even if you can afford 3AWG copper, you may choose 3AWG aluminum because the material is easier to install.

Does Temperature Affect 3-Gauge Wiring Amps?

The temperature is even more important than the material. Again, look at the wire size chart. Have you noticed that a 3-gauge wire’s amps increase with the temperature? The gauge will carry 85A at 60 degrees C and 110 amps at 90 degrees C.

Your primary concern is a wire’s internal temperature and ambient temperature. The internal temperature matters because conductors resist the flow of current. This is why they become warm to the touch when you connect them to a load.

Pairing a wire with a larger load than it can handle will lead to overheating. The wire in question will melt. 3AWG lines are extremely thick. But that doesn’t mean they are immune to overheating.

The ambient temperature is dangerous because it can contribute to overheating. This is where the temperature rating shines. A wire with a high-temperature rating can accommodate a large load in a setting with poor ventilation without overheating.

This is why a 3-gauge wire’s amps increase with the temperature rating. The higher the temperature rating, the greater the ampacity.

Distance vs 3-Gauge Wire

For Copper Wire,

Single Phase

VoltageAmpVoltage DropMax Distance
120 V853%99 ft
240 V853%198 ft
480 V853%397 ft

Three Phase

VoltageAmpVoltage DropMax Distance
120853%114 ft
240853%229 ft
480853%459 ft

Do The Watts Matter?

If a 3AWG wire has an ampacity of 85 amps, you can get the watts when you multiply 85 by 120V. This gives you 10,200 watts. A 240V system will change the watts. However, you find the wattage on appliances. The watts don’t matter to a wire.

You can change a machine’s wattage to amps to compare its power consumption to a wire’s amp rating.


Stellar is an engineer. He has an unconventional approach to problem-solving, and is adept at devising original solutions to complex issues. He is an imaginative thinker and regularly comes up with resourceful answers to challenging problems.

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