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RV

Wire Ampacity Ratings & Voltage Drops

Grand Canyon - Photo of the south rim of the Grand Canyon covered in snow during the winter

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
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