How to Calculate Voltage Drop for Long Paired Wire Runs

A primary concern when installing lengths of wire is voltage drop. The amount of voltage lost between the originating power supply and the device being powered can be significant. Improper selection of wire gauge can lead to an unacceptable loss of power at the load end. The following calculator is designed to help calculate power loss for a given wire gauge and load current, as well as a comparison of three other wire gauges and the benifit in power los reduction and cost.

(Note: It just calculates the voltage drop, consult your local or national electrical code or your electrician to decide what is legal!)
Settings
Select Copper or Aluminum wire 
Select American Wire Gauge (AWG) Size
Select Voltage Type
Enter opperating Voltage
Enter 1-way circuit length in feet
Enter Load in amps
Cost per kilowat hour from utility company: .
Wire cost per foot .
Hours per day wire length is utilized .
Totals
Voltage drop
Voltage at load end of circuit
Percent voltage or wattage drop
Wattage Loss
Wattage Gain Dude To Upgrade
Source Wattage
Hours of usage to recover cost of upgrade
Days of usage to recover cost of upgrade
Months of usage to recover cost of upgrade
Years of usage to recover cost of upgrade
Total Wire Cost
Comparison 1
.

Totals
Comparison 2

Totals
Comparison 3

Totals

EXAMPLE ONE:

Given a load current of 1 AMP, and using 18 AWG wire, how much voltage drop can we expect at the load end for a 350 foot run of paired wire?

Using the chart, we match the row for 18 AWG and the column for 1 AMP and determine that voltage drop per 100 feet is 1.27 Volts. By dividing the paired wire length by 100, we get the factor by which we need to multiply voltage drop per 100 feet to determine total voltage drop. Therefore, 350 feet divided by 100 equals 3.5. Multiply 3.5 by 1.27 volts drop per 100 feet to get your total voltage drop. Thus the total voltage drop is 3.5 times 1.27, or 4.445 voltage drop for 350 feet.

EXAMPLE TWO:

Given a camera load of 2 AMPs, that is 400 feet from the power source, which wire gauge should be selected to keep voltage drop at the camera to less than 3 volts?

To use the chart, we need to determine what the maximum voltage drop per 100 feet is. We calculate that 100 feet is 1/4 of 400 feet, thus the voltage drop allowed for 100 feet is 1/4 times 3 volts (which is the equivalent of 0.75 volts per 100 feet):

voltage drop per 100 feet = 3/4 = .75 volts per 100 feet. 


 

Amperage that is needed to heat up the insulation to a certain temperature (Copper Cable / different Insulation Materials) in free air (30C)

AWG

POLYPROPYLENE, POLYETHYLENE,
(high density) at 90C

PVC (irradiated), NYLON at 105C

KAPTON, TEFLON, SILICONE at 200C

30

3 A

3 A

4 A

28

4 A

4 A

6 A

26

5 A

5 A

7 A

24

7 A

7 A

10 A

22

9 A

10 A

13 A

20

12 A

13 A

17 A

18

17 A

18 A

24 A

16

22 A

24 A

32 A

14

30 A

33 A

45 A

12

40 A

45 A

55 A

10

55 A

58 A

75 A

8

70 A

75 A

100 A

6

100 A

105 A

135 A

4

135 A

145 A

180 A

2

180 A

200 A

240 A



AWG Wire Sizes (see table below)

AWG: In the American Wire Gauge (AWG), diameters can be calculated by applying the formula D(AWG)=.00592((36-AWG)/39) inch. For the 00, 000, 0000 etc. gauges you use -1, -2, -3, which makes more sense mathematically than "double nought." This means that in American wire gage every 6 gauge decrease gives a doubling of the wire diameter, and every 3 gauge decrease doubles the wire cross sectional area. Just like dB in signal levels.


Metric Wire Gauges (see table below)
Metric Gauge: In the Metric Gauge scale, the gauge is 10 times the diameter in millimeters, so a 50 gauge metric wire would be 5 mm in diameter. Note that in AWG the diameter goes up as the gauge goes down, but for metric gauges it is the opposite. Probably because of this confusion, most of the time metric sized wire is specified in millimeters rather than metric gauges.

Load Carrying Capacities (see table below)
The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility.
AWG gauge Diameter Inches Diameter mm Ohms per 1000 ft Ohms per km Maximum amps for chassis wiring Maximum amps for power transmission
OOOO 0.46 11.684 0.049 0.16072 380 302
OOO 0.4096 10.40384 0.0618 0.202704 328 239
OO 0.3648 9.26592 0.0779 0.255512 283 190
0 0.3249 8.25246 0.0983 0.322424 245 150
1 0.2893 7.34822 0.1239 0.406392 211 119
2 0.2576 6.54304 0.1563 0.512664 181 94
3 0.2294 5.82676 0.197 0.64616 158 75
4 0.2043 5.18922 0.2485 0.81508 135 60
5 0.1819 4.62026 0.3133 1.027624 118 47
6 0.162 4.1148 0.3951 1.295928 101 37
7 0.1443 3.66522 0.4982 1.634096 89 30
8 0.1285 3.2639 0.6282 2.060496 73 24
9 0.1144 2.90576 0.7921 2.598088 64 19
10 0.1019 2.58826 0.9989 3.276392 55 15
11 0.0907 2.30378 1.26 4.1328 47 12
12 0.0808 2.05232 1.588 5.20864 41 9.3
13 0.072 1.8288 2.003 6.56984 35 7.4
14 0.0641 1.62814 2.525 8.282 32 5.9
15 0.0571 1.45034 3.184 10.44352 28 4.7
16 0.0508 1.29032 4.016 13.17248 22 3.7
17 0.0453 1.15062 5.064 16.60992 19 2.9
18 0.0403 1.02362 6.385 20.9428 16 2.3
19 0.0359 0.91186 8.051 26.40728 14 1.8
20 0.032 0.8128 10.15 33.292 11 1.5
21 0.0285 0.7239 12.8 41.984 9 1.2
22 0.0254 0.64516 16.14 52.9392 7 0.92
23 0.0226 0.57404 20.36 66.7808 4.7 0.729
24 0.0201 0.51054 25.67 84.1976 3.5 0.577
25 0.0179 0.45466 32.37 106.1736 2.7 0.457
26 0.0159 0.40386 40.81 133.8568 2.2 0.361
27 0.0142 0.36068 51.47 168.8216 1.7 0.288
28 0.0126 0.32004 64.9 212.872 1.4 0.226
29 0.0113 0.28702 81.83 268.4024 1.2 0.182
30 0.01 0.254 103.2 338.496 0.86 0.142
31 0.0089 0.22606 130.1 426.728 0.7 0.113
32 0.008 0.2032 164.1 538.248 0.53 0.091
Metric 2.0 0.00787 0.200 169.39 555.61 0.51 0.088
33 0.0071 0.18034 206.9 678.632 0.43 0.072
Metric 1.8 0.00709 0.180 207.5 680.55 0.43 0.072
34 0.0063 0.16002 260.9 855.752 0.33 0.056
Metric 1.6 0.0063 0.16002 260.9 855.752 0.33 0.056
35 0.0056 0.14224 329 1079.12 0.27 0.044
Metric 1.4 .00551 .140 339 1114 0.26 0.043
36 0.005 0.127 414.8 1360 0.21 0.035
Metric 1.25 .00492 0.125 428.2 1404 0.20 0.034
37 0.0045 0.1143 523.1 1715 0.17 0.0289
Metric 1.12 .00441 0.112 533.8 1750 0.163 0.0277
38 0.004 0.1016 659.6 2163 0.13 0.0228
Metric 1 .00394 0.1000 670.2 2198 0.126 0.0225
39 0.0035 0.0889 831.8 2728 0.11 0.0175
40 0.0031 0.07874 1049 3440 0.09 0.0137
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