If you want 80 amp service, you have to adequately size your breaker and pick the right sized wire. This is not all that simple, since we have to account for National Electricity Code (NEC) rules. To help everybody out with 80 amp circuits, we are going to answer both of these questions:
- What size wire do you need for an 80 amp breaker? We would immediately think that a wire that can handle 80 amps is appropriate. However, accounting for the 80% NEC rule, we will see that you actually need a thinner wire.
- What size wire do you need for 80 amp service? What if we run that 80 amp wire for 50 feet, 100 feet, 150 feet, 200 feet, or even 400 feet? Here we will have to look at copper and aluminum wire ampacity. Even more vital is accounting for voltage drop that happens in longer wires (50+ feet long wires).
First, we will look at the 80-amp breaker wire size. This is quite easy. Figuring out an 80 amp wire size for a sub-panel or service at a distance is more challenging. We are going to show how to adequately size a wire for an 80 amp circuit by, very importantly, accounting for voltage drop. Since math is not exactly easy, we have prepared these two useful resources that simply things:
- 80 Amp Wire Size Calculator. This calculator will determine the wire size for 80 amp current based on all relevant inputs, including wire length, voltage (12V, 120V, 220V, for example), and allowable voltage drop percentage (3%, 5%, 10%, and so on).
- 80 Amp Wire Gauge Charts. We have calculated the wire sizes for 12V, 120V, and 220V voltages with wire lengths between 0 and 500 feet, and allowable voltage drop of 3% for crucial circuits and a 10% voltage drop for non-crucial circuits. The results of these wires sizes (AWG, kcmil copper wires) are gathered in 2 all-encompassing charts.
Now, let’s start with the easy part; the wire size for an 80 amp breaker.
80 Amp Breaker Wire Size
The amp breaker protects us from the current surges. To do that job well, the NEC code states that a breaker can only be loaded up to 80% of its capacity. This is known as the breaker NEC 80% rule.
That means that you can’t put 80 amps on an 80 amp breaker. That would be 100% of its capacity. According to the electrical code, we can only put 64 amps on the 80A breaker since 64 amps is 80% of its capacity.
For 80 amp wire sizes, that means that:
- We don’t need a wire that can handle 80 amps for an 80A breaker.
- We need a wire that can handle up to only 64 amps for an 80A breaker.
Looking at the copper and aluminum ampacity chart (here is this NEC 310.16 Table), we can see which wire can handle these 64 amps. Here is the screenshot for copper and aluminum wires (we are looking at the median temperature ampacities at 75°C (167°F)):
From this chart, we can clearly see (in red markings) that we need:
- 6 AWG copper wire for 80 amp breaker. It can handle up to 65 amps which is more than the required 64 amps.
- 4 AWG copper wire for 80 amp breaker. We have the same situation here; the ampacity is 65A which is more than the 64 amps we need for an 80A breaker.
That’s quite easy, right? Now let’s move to a bit harder part. We are going to look into everything you need to know to correctly size a 80 amp wire:
How To Calculate 80 Amp Wire Gauge? (AWG, kcmil)
For an 80 amp circuit, we have to use the 80 amp wire. If you check the screenshot from the NEC 310.16 Article above, we can see that:
- 4 AWG copper wire is used for 80 amp service. This wire has 85A ampacity and can handle 85 amps, more than the required 80 amps.
- 2 AWG aluminum wire is used for 80 amp service. This wire has 95A ampacity and can handle 95 amps, way more than 60 amps required.
Now, this is true if we have short wires. If, however, we have long wires, we have to account for voltage drop. Due to voltage drop, we have to use thicker wires. NEC code provides us with these maximum allowable drops:
- 3% allowable voltage drop for branch circuits.
- 5% allowable voltage drop for feeders.
- 10% allowable voltage drop for general appliances and general lighting.
How thicker should a wire be if we want 80 amps at a distance of 100 feet, 200 feet, and so on? To calculate the 80 amp wire size, we have to use these two equations:
Vd = 2 × L × K × 80 Amps / CM and Vd = Voltage Drop Percentage × Voltage / 100
If we combine these two equations and express CM (these are circular mils we are going to use to figure out AWG or kcmil wire size), we get this:
CM = 2 × L × K × 80 Amps × 100 / Voltage Drop Percentage × Voltage
Here the L is wire length and K is the specific material resistivity (12.9 ohms for copper wires and 21.2 for aluminum wires). Let’s solve one quick example to illustrate 80 amp wire calculation; the calculator further on does this calculation automatically, and the 2 charts contain all the wire sizes you need.
Suppose we want to run a 100 feet wire on a 120V circuit. We want to get 80 amp service, and we use a 3% allowable voltage drop. Let’s put all of this in the formula above like this:
CM = 2 × 100 Ft × 12.9 Ohms × 80 Amps × 100 / 3% × 120V = 57,333 Circular Mils
We see that the adequately sized wire for this 80 amp circuit has more than 57,333 circular mils cross-section area. Which AWG wire is that? Let’s consult this AWG to circular mils chart to figure that out; here is the screenshot:
We see that we have to use 2 AWG copper wire since it has more than the minimum required 57,333 circular mils cross-section area (66,369 circular mils, to be exact).
If you use the same numbers in the calculator, you will get the same result.
Here is the calculator. Just insert the wire length, voltage, and maximal allowable voltage drop, and the calculator will automatically determine the wire size. Note: This calculator accounts for voltage drop well, but always remember that you have to use a 4 AWG copper or thicker wire for all 80 amp currents since this wire has 85A ampacity:
80 Amp Wire Size Calculator (Accounted For Voltage Drop)
To illustrate how this calculator works, let’s use the example we manually calculated. Slide the 1st wire length slider to ‘100’ since we have 100 feet wire, the 2nd voltage slider to ‘120’ since we have 120V voltage, and the 3rd voltage drop slider to ‘3’ since we have 3% allowable voltage drop.
We get the same result: For this 80 amp circuit, we need a 2 AWG copper wire.
This is just one example. In the chart below, you will see listed 80 wire gauges for 12V, 120V, and 220V voltages for a wire length ranging from 0 to 500 feet, and for 3% allowable voltage drop (1st chart) as well as for 10% allowable voltage drop (2nd chart):
80 Amp Wire Gauge Source 0-500 Feet Away (3% Allowable Voltage Drop)
|Wire Length (3% Vd):||80 Amp Wire Size At 12V:||80 Amp Wire Size At 120V:||80 Amp Wire Size At 220V:|
|0 Feet||4 AWG Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|50 Feet||300 kcmil Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|100 Feet||600 kcmil Copper Wire||2 AWG Copper Wire||4 AWG Copper Wire|
|150 Feet||900 kcmil Copper Wire||1/0 AWG Copper Wire||3 AWG Copper Wire|
|200 Feet||1250 kcmil Copper Wire||2/0 AWG Copper Wire||2 AWG Copper Wire|
|300 Feet||1750 kcmil Copper Wire||4/0 AWG Copper Wire||1/0 AWG Copper Wire|
|400 Feet||2 Or More Wires||250 kcmil Copper Wire||2/0 AWG Copper Wire|
|500 Feet||2 Or More Wires||300 kcmil Copper Wire||3/0 AWG Copper Wire|
We see that we need increasingly thicker wires if the wire length increases and for lower voltages.
Here is what size wire we need for an 80 amp circuit 200 feet away at a 3% allowable voltage drop:
- At 12V, we need a 1250 kcmil copper wire. Voltage drop is very significant at lower voltages, hence a very thick wire.
- At 120V, we need a 2/0 AWG copper wire.
- At 220V, we need 2 AWG copper wire.
As we can see, the voltage drop is not all that significant at higher 220V voltage. We went from 4 AWG at 0 feet to 2 AWG at 200 feet.
Now, let’s have a look at a looser 10% allowable voltage drop chart for 80 amp service:
80Amp Wire Gauge Source 0-500 Feet Away (10% Allowable Voltage Drop)
|Wire Length (10% Vd):||80 Amp Wire Size At 12V:||80 Amp Wire Size At 120V:||80 Amp Wire Size At 220V:|
|0 Feet||4 AWG Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|50 Feet||1/0 AWG Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|100 Feet||4/0 AWG Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|150 Feet||300 kcmil Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|200 Feet||350 kcmil Copper Wire||4 AWG Copper Wire||4 AWG Copper Wire|
|300 Feet||600 kcmil Copper Wire||3 AWG Copper Wire||4 AWG Copper Wire|
|400 Feet||700 kcmil Copper Wire||1 AWG Copper Wire||4 AWG Copper Wire|
|500 Feet||900 kcmil Copper Wire||1/0 AWG Copper Wire||3 AWG Copper Wire|
Here we see that we don’t need such thick wires as at a 3% allowable voltage drop. Namely, if we have a 200 feet wire and want 80 amps with a 10% allowable voltage drop, we have to use:
- 350 kcmil copper wire at 12V.
- 4 AWG copper wire at 120V.
- 4 AWG copper wire at 220V.
Despite the 80 amp service being 200 feet away, we still use the regular 4 AWG copper wire for 80 amp current at 120V and 220V.
We hope that this illustrates well how to size an 80 amp wire. Using the calculator and consulting these charts, you can now have all you need for sizing 80 amp wires. If you need help, you can use the comment section below, give us some numbers, and we will help you with the math.
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