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.
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 (30°C)  
AWG 
POLYPROPYLENE,
POLYETHYLENE, 
PVC
(irradiated), NYLON at 105°C 
KAPTON, TEFLON,
SILICONE at 200°C 
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)=.005·92^{((36AWG)/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.
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 
; 