The information that follows is all available at a variety of locations online. I’m aggregating and re-posting it for only one reason: easier access. While doing my solar installation, it was a challenge to keep track of which site had which piece of data. Some only had up to 90°C while others were limited in which wire gauges they showed. In my experience, this information should cover virtually all needs — AWG when dealing with imperial units, mm^2 when referencing metric documentation (e.g., Victron’s inverter manual), and the ampacity ratings for the most common wire insulation temperatures.
Copper Wire Ampacity
105°C, 90°C, 75°C, and 60°C are insulation temperature ratings.
| Wire Size (AWG) | Nominal Diameter | mm^2 | 105°C | 90°C | 75°C | 60°C |
|---|---|---|---|---|---|---|
| 18 | 7/64″ | 0.823 | 20 | 14 | ||
| 16 | 1/8″ | 1.31 | 25 | 18 | ||
| 14 | 9/64″ | 2.08 | 35 | 25 | 20 | 15 |
| 12 | 5/32″ | 3.31 | 45 | 30 | 25 | 20 |
| 10 | 7/32″ | 5.26 | 60 | 40 | 35 | 30 |
| 8 | 5/16″ | 8.37 | 80 | 55 | 50 | 40 |
| 6 | 11/32″ | 13.30 | 120 | 75 | 65 | 55 |
| 4 | 13/32″ | 21.15 | 160 | 95 | 85 | 70 |
| 2 | 15/32″ | 33.62 | 210 | 130 | 115 | 95 |
| 1 | 17/32″ | 44.21 | 245 | 145 | 130 | 110 |
| 1/0 | 9/16″ | 53.49 | 285 | 170 | 150 | 125 |
| 2/0 | 5/8″ | 67.43 | 330 | 195 | 175 | 145 |
| 3/0 | 11/16″ | 85.01 | 385 | 225 | 200 | 165 |
| 4/0 | 13/16″ | 107.20 | 445 | 260 | 230 | 195 |
Ampacity Correction Factors
The ampacity of a wire is based on the temperature its insulation can handle. For obvious reasons, the colder the ambient is, the more it can carry. Standard ratings are based on an ambient temperature no warmer than 86°F (30°C). If the ambient temperature is outside of the range 78-86°F (26-30°C), multiply the ampacity rating by the corresponding multiplier below:
| Ambient Temperature | 105°C | 90°C | 75°C | 60°C |
|---|---|---|---|---|
| 70-77°F (21-25°C) | 1.02 | 1.02 | 1.03 | 1.04 |
| 78-86°F (26-30°C) | 1 | 1 | 1 | 1 |
| 87-95°F (31-35°C) | 0.96 | 0.96 | 0.94 | 0.91 |
| 96-104°F (36-40°C) | 0.92 | 0.91 | 0.88 | 0.82 |
| 105-113°F (41-45°C) | 0.88 | 0.87 | 0.82 | 0.71 |
| 114-122°F (46-50°C) | 0.84 | 0.82 | 0.75 | 0.58 |
| 123-131°F (51-55°C) | 0.80 | 0.76 | 0.67 | 0.41 |
| 132-140°F (56-60°C) | 0.75 | 0.71 | 0.58 | |
| 141-158°F (61-70°C) | 0.65 | 0.58 | 0.33 | |
| 159-176°F (71-80°C) | 0.54 | 0.41 | ||
| 177-194°F (81-90°C) | 0.40 |
Group Correction Factors
When wires are are touching, a correction factor is also needed to compensate for a combined temperature rise.
| Number of Wires | Bundled, Single Layer | Enclosed or Multiple Layers |
|---|---|---|
| 2 | 0.85 | 0.80 |
| 3 | 0.79 | 0.70 |
| 4 | 0.75 | 0.65 |
| 5 | 0.73 | 0.60 |
| 6 | 0.72 | 0.57 |
| 7 | 0.71 | 0.54 |
| 8 | 0.70 | 0.52 |
| 9 | 0.50 | |
| 10 | 0.48 | |
| 12 | 0.45 | |
| 14 | 0.43 | |
| 16 | 0.41 | |
| 18 | 0.39 | |
| 20 | 0.38 |
Voltage Drop
Voltage drops along a circuit in direct relation to the length of the circuit and the amperage being carried. For a 12V nominal system using 105°C wire, the tables below specify the minimum wire size for a given circuit length (the sum of both the the positive and negative wire lengths) and the current carried.
The voltage drop is defined by ΔV = A × L × Ω
<= 1% Drop
| Length | 5A | 10A | 15A | 20A | 25A | 30A | 40A | 50A | 60A | 70A | 80A | 90A | 100A |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10 ft | 12 | 10 | 8 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1 | 1/0 |
| 15 ft | 10 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 1/0 | 2/0 | 2/0 |
| 20 ft | 10 | 6 | 6 | 4 | 4 | 2 | 1 | 1/0 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 |
| 25 ft | 8 | 6 | 4 | 4 | 2 | 2 | 1/0 | 2/0 | 2/0 | 3/0 | 4/0 | 4/0 | |
| 30 ft | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | 4/0 | ||
| 40 ft | 6 | 4 | 2 | 1 | 1/0 | 1/0 | 3/0 | 4/0 | 4/0 | ||||
| 50 ft | 6 | 4 | 2 | 1/0 | 2/0 | 2/0 | 4/0 | ||||||
| 60 ft | 6 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | ||||||
| 70 ft | 4 | 2 | 1/0 | 2/0 | 3/0 | 4/0 | |||||||
| 80 ft | 4 | 1 | 1/0 | 3/0 | 4/0 | 4/0 | |||||||
| 90 ft | 4 | 1 | 2/0 | 3/0 | 4/0 | ||||||||
| 100 ft | 4 | 1/0 | 2/0 | 4/0 | |||||||||
| 110 ft | 2 | 1/0 | 3/0 | 4/0 | |||||||||
| 120 ft | 2 | 1/0 | 3/0 | 4/0 | |||||||||
| 130 ft | 2 | 2/0 | 4/0 | ||||||||||
| 140 ft | 2 | 2/0 | 4/0 | ||||||||||
| 150 ft | 2 | 2/0 | 4/0 | ||||||||||
| 160 ft | 1 | 3/0 | 4/0 | ||||||||||
| 170 ft | 1 | 3/0 |
<= 3% Drop
| Length | 5A | 10A | 15A | 20A | 25A | 30A | 40A | 50A | 60A | 70A | 80A | 90A | 100A |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10 ft | 18 | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 6 | 4 |
| 15 ft | 16 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 4 | 4 | 4 | 4 |
| 20 ft | 14 | 12 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 4 | 2 | 2 | 2 |
| 25 ft | 14 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 4 | 2 | 2 | 2 | 1 |
| 30 ft | 12 | 10 | 8 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1 | 1/0 |
| 40 ft | 12 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1 | 1/0 | 1/0 | 2/0 |
| 50 ft | 10 | 8 | 6 | 4 | 4 | 4 | 2 | 1 | 1/0 | 1/0 | 2/0 | 2/0 | 3/0 |
| 60 ft | 10 | 6 | 6 | 4 | 4 | 2 | 1 | 1/0 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 |
| 70 ft | 10 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 |
| 80 ft | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 | |
| 90 ft | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | 4/0 | ||
| 100 ft | 8 | 4 | 4 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | 4/0 | |||
| 110 ft | 8 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | ||||
| 120 ft | 6 | 4 | 2 | 1 | 1/0 | 1/0 | 3/0 | 4/0 | 4/0 | ||||
| 130 ft | 6 | 4 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | |||||
| 140 ft | 6 | 4 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | |||||
| 150 ft | 6 | 4 | 2 | 1/0 | 2/0 | 2/0 | 4/0 | ||||||
| 160 ft | 6 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | ||||||
| 170 ft | 6 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 |
<= 5% Drop
| Length | 5A | 10A | 15A | 20A | 25A | 30A | 40A | 50A | 60A | 70A | 80A | 90A | 100A |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 10 ft | 18 | 16 | 16 | 14 | 12 | 12 | 10 | 10 | 10 | 8 | 8 | 8 | 6 |
| 15 ft | 18 | 16 | 14 | 12 | 10 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 6 |
| 20 ft | 16 | 14 | 12 | 10 | 10 | 10 | 8 | 6 | 6 | 6 | 4 | 4 | 4 |
| 25 ft | 16 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 6 | 4 | 4 | 4 | 4 |
| 30 ft | 16 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 4 | 2 | 2 |
| 40 ft | 14 | 10 | 10 | 8 | 6 | 6 | 4 | 4 | 4 | 2 | 2 | 2 | 1 |
| 50 ft | 12 | 10 | 8 | 6 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1 | 1/0 |
| 60 ft | 12 | 10 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 1/0 | 1/0 |
| 70 ft | 10 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 1/0 | 2/0 | 2/0 |
| 80 ft | 10 | 8 | 6 | 4 | 4 | 4 | 2 | 1 | 1/0 | 1/0 | 2/0 | 2/0 | 3/0 |
| 90 ft | 10 | 8 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 2/0 | 3/0 | 3/0 |
| 100 ft | 10 | 6 | 6 | 4 | 4 | 2 | 1 | 1/0 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 |
| 110 ft | 10 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 2/0 | 3/0 | 4/0 | 4/0 |
| 120 ft | 10 | 6 | 4 | 4 | 2 | 2 | 1/0 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 |
| 130 ft | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 | 4/0 | |
| 140 ft | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | 4/0 | ||
| 150 ft | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | 4/0 | ||
| 160 ft | 8 | 4 | 4 | 2 | 1 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 | |||
| 170 ft | 8 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 | 4/0 |