8 Gauge Wire (8/2 Wire, 8/3 Wire, 8/4 Wire): How Many Amps Can 8 Gauge Wire Handle

8 gauge wire is a very popular wire commonly often used for applications requiring wire that can handle dozens of Amps with minimal energy losses.

However, the Ampacity of the wire depends on the wire thickness, but also it depends on the wire length, maximum wire surface temperature, wire material, wire construction, etc.

Updated: August 8, 2022.

8 Gauge Wire Dimensions

The physical dimensions of the solid copper 8 gauge wire are:

- Diameter: 3.2636 mm, 0.1285 inches,

- Cross Section: 8.3656 mm², 0.0130 inches².

We emphasize this "solid copper" part because 8 gauge wires can be:

- Solid or Stranded: Solid wires are harder to bend and generally more difficult to work with. On the other hand, stranded 8 gauge wires are easier to work with, but their diameter and cross-section are a little bit larger in order to ensure the same Ampacity (current carrying ability). For example, some very fine stranded 8 gauge copper wires (1650/0.08 mm) feature a diameter of ~3.76 mm.

- Copper or Aluminum: copper is heavier and more expensive than aluminum, but it is also a better conductor. While aluminum wires are lighter for the same Ampacity, they are actually thicker. On the other spectrum of prices are Oxygen-Free Copper (OFC) wires which are sold in several grades - lower resistance than "classic" copper wires, but also more expensive and for most applications benefits of OFC wires don't justify their higher price.

- Copper Clad Aluminum (CCA): CCA wires feature an aluminum core and outer copper cladding. CCA wires are lighter and cheaper than copper wires but have higher resistance. CCA wires are very popular speaker wires - they are cheaper than copper wires and due to the outer copper cladding, in theory, they are less prone to skin effect issues than pure aluminum wires.

However, the skin effect has a very low impact on losses for signals up to 20 kHz.

8 Gauge Wire Ampacity

If we check the Ampacity of the 8 gauge solid copper wire, then we can see that the Ampacity depends on the temperature:

- @60°C/140°F: 40 Amps,

- @75°C/167°F: 50 Amps,

- @90°C/194°F: 55 Amps.

Although many modern wires have a rather broad range of operating temperatures (sometimes from -60°C to 200°C), for most applications, especially at home, we MUST use the Ampacity value for 60°C/140°F, which is 40 Amps.

And this is just the default Ampacity for 8 gauge solid copper wire.

80% Rule

For safety reasons, one has to increase the required Ampacity using the "80% Rule":

- @60°C/140°F: 40 Amps * 0.8 = 32 Amps,

- @75°C/167°F: 50 Amps * 0.8 = 40 Amps,

- @90°C/194°F: 55 Amps * 0.8 = 44 Amps.

So, the actual Ampacity of the 8 gauge solid copper wire @60°C/140°F is 32 Amps and NOT the default 40 Amps.

And this is just for shorter wires.

Wire Length

As the wire length is increased, the wire electric resistance and thus energy losses increase.

To keep the energy losses at an acceptable level, for every 50 feet, we calculate a 10% smaller Ampacity.

For example, the actual Ampacity for a 100 feet long 8 gauge wire with the maximum allowed surface temperature of 60°C/140°F would be:

Ampacity = 40 * 0.8 / 1.2 = 26.66 Amps

The following chart lists the Ampacity (given in Amps) of 8 gauge wire at certain temperatures for the wires of 50, 100, 150, and 200 feet.

Note: for most applications, one has to use an external wire temperature of 60°C/140°F, despite many wires being able to operate safely at 100+ °C. If unsure, check the local laws and regulations and/or consult a locally certified electrician.

So, from the default Ampacity of 40 Amps for a solid copper 8 gauge wire, we came to 22.8 Amps for the same wire 200 feet long - so 200 feet long solid copper 8 gauge wire can handle 22.8 Amps.

Note: as the wire is longer and the current through the wire is weaker, energy losses per foot of the wire decrease, which means that the wire will have a surface temperature below 60°C/140°F. However, with the increase in the wire length, total energy losses must be taken into account.

8 Gauge Marine/Automotive Wire

Marine/automotive 8 gauge wires are usually stranded 8 gauge copper wires with increased resistance to mechanical wear, high and low temperatures, acidic and alkalic environments, etc.

In order to increase their durability, some manufacturers even offer stranded copper wires with tinned copper strands, increasing the resistance to oxidation and other chemical reactions.

Of course, such wires are more expensive, but for aggressive environments, one can't go cheap with wiring... better safe than sorry!

8 Gauge Wire Cables: 8/2 Wire, 8/3 Wire, and 8/4 Wire

Electric cables consist of several wires bundled together. The actual number of wires varies depending on the intended cable use.

Hence, cables made using 8 gauge wires are labeled as 8/2 Wire (also written as "8 2 Wire"), 8/3 Wire (8 3 Wire), and 8/4 Wire (8 4 Wire).

When the cable is labeled as, for example, "8/3 Wire", that means that it is a cable consisting of three 8 gauge wire conductors and one ground wire. Thus:

• 8/2 Wire (8 2 Wire) consists of two 8 gauge wire conductors and one ground wire.
• 8/3 Wire (8 3 Wire) consists of three 8 gauge wire conductors and one ground wire.
• 8/4 Wire (8 4 Wire) consists of four 8 gauge wire conductors and one ground wire.

Note: ground wires are not necessarily 8 gauge wires.

In order to help the user properly connect the wires, they are color-coded - the actual color codes depend on the intended wire/cable use and the country.