Voltage Drop Calculator

Result

Voltage drop: 3.17
Voltage drop percentage: 26.42%
Voltage at the end: 8.83

Please note that the result is an estimation based on normal condition. The actual voltage drop can vary depend on the condition of the wire, the conduit being used, the temperature, the connector, the frequency etc. But, in most cases, it will be very close.



Wire Material
Wire Size
Voltage
Phase
Number of conductors
Distance*
Load current Amps
 
* Please use one-way distance to the load. Not round trip distance.

Basic Voltage Drop Law

Vdrop = IR

where:
I : the current through the object, measured in amperes
R : the resistance of the wires, measured in ohms


Typical AWG wire sizes

AWG Diameter Turns of wire Area Copper resistance NEC copper wire ampacity with 60/75/90°C insulation (A) Approximate stranded metric equivalents
(inch) (mm) (per inch) (per cm) (kcmil) (mm2) (O/km) (O/kFT)
0000 (4/0) 0.4600 11.684 2.17 0.856 212 107 0.1608 0.04901 195 / 230 / 260  
000 (3/0) 0.4096 10.404 2.44 0.961 168 85.0 0.2028 0.06180 165 / 200 / 225  
00 (2/0) 0.3648 9.266 2.74 1.08 133 67.4 0.2557 0.07793 145 / 175 / 195  
0 (1/0) 0.3249 8.252 3.08 1.21 106 53.5 0.3224 0.09827 125 / 150 / 170  
1 0.2893 7.348 3.46 1.36 83.7 42.4 0.4066 0.1239 110 / 130 / 150  
2 0.2576 6.544 3.88 1.53 66.4 33.6 0.5127 0.1563 95 / 115 / 130  
3 0.2294 5.827 4.36 1.72 52.6 26.7 0.6465 0.1970 85 / 100 / 110 196/0.4
4 0.2043 5.189 4.89 1.93 41.7 21.2 0.8152 0.2485 70 / 85 / 95  
5 0.1819 4.621 5.50 2.16 33.1 16.8 1.028 0.3133   126/0.4
6 0.1620 4.115 6.17 2.43 26.3 13.3 1.296 0.3951 55 / 65 / 75  
7 0.1443 3.665 6.93 2.73 20.8 10.5 1.634 0.4982   80/0.4
8 0.1285 3.264 7.78 3.06 16.5 8.37 2.061 0.6282 40 / 50 / 55  
9 0.1144 2.906 8.74 3.44 13.1 6.63 2.599 0.7921   84/0.3
10 0.1019 2.588 9.81 3.86 10.4 5.26 3.277 0.9989 30 / 35 / 40
11 0.0907 2.305 11.0 4.34 8.23 4.17 4.132 1.260   56/0.3
12 0.0808 2.053 12.4 4.87 6.53 3.31 5.211 1.588 25 / 25 / 30 (20)  
13 0.0720 1.828 13.9 5.47 5.18 2.62 6.571 2.003   50/0.25
14 0.0641 1.628 15.6 6.14 4.11 2.08 8.286 2.525 20 / 20 / 25 (15)  
15 0.0571 1.450 17.5 6.90 3.26 1.65 10.45 3.184   30/0.25
16 0.0508 1.291 19.7 7.75 2.58 1.31 13.17 4.016 - / - / 18 (10)
17 0.0453 1.150 22.1 8.70 2.05 1.04 16.61 5.064   32/0.2
18 0.0403 1.024 24.8 9.77 1.62 0.823 20.95 6.385 - / - / 14 (7) 24/0.2
19 0.0359 0.912 27.9 11.0 1.29 0.653 26.42 8.051  
20 0.0320 0.812 31.3 12.3 1.02 0.518 33.31 10.15   16/0.2
21 0.0285 0.723 35.1 13.8 0.810 0.410 42.00 12.80   13/0.2
22 0.0253 0.644 39.5 15.5 0.642 0.326 52.96 16.14   7/0.25
23 0.0226 0.573 44.3 17.4 0.509 0.258 66.79 20.36    
24 0.0201 0.511 49.7 19.6 0.404 0.205 84.22 25.67   1/0.5, 7/0.2, 30/0.1
25 0.0179 0.455 55.9 22.0 0.320 0.162 106.2 32.37    
26 0.0159 0.405 62.7 24.7 0.254 0.129 133.9 40.81   7/0.15
27 0.0142 0.361 70.4 27.7 0.202 0.102 168.9 51.47    
28 0.0126 0.321 79.1 31.1 0.160 0.0810 212.9 64.90    
29 0.0113 0.286 88.8 35.0 0.127 0.0642 268.5 81.84    
30 0.0100 0.255 99.7 39.3 0.101 0.0509 338.6 103.2   1/0.25, 7/0.1
31 0.00893 0.227 112 44.1 0.0797 0.0404 426.9 130.1    
32 0.00795 0.202 126 49.5 0.0632 0.0320 538.3 164.1   1/0.2, 7/0.08
33 0.00708 0.180 141 55.6 0.0501 0.0254 678.8 206.9    
34 0.00630 0.160 159 62.4 0.0398 0.0201 856.0 260.9    
35 0.00561 0.143 178 70.1 0.0315 0.0160 1079 329.0    
36 0.00500 0.127 200 78.7 0.0250 0.0127 1361 414.8    
37 0.00445 0.113 225 88.4 0.0198 0.0100 1716 523.1    
38 0.00397 0.101 252 99.3 0.0157 0.00797 2164 659.6    
39 0.00353 0.0897 283 111 0.0125 0.00632 2729 831.8    
40 0.00314 0.0799 318 125 0.00989 0.00501 3441 1049    

When electrical current moves through a wire it must surpass a certain level of contrary pressure. If the current is alternating, such pressure is called impedance. Impedance is a vector, or two-dimensional quantity, consisting of resistance and reactance (reaction of a built up electric field to a change of current). If the current is direct, the pressure is called resistance.

All this sounds terribly abstract, but it's really not much different from water running through a garden hose. It takes a certain amount of pressure to push the water through the hose, which is like voltage for electricity. Current is like the water flowing through the hose. And the hose causes a certain level of resistance, depending on its thickness, shape, etc. The same kind of thing is true for wires, as their type and size determines the level of resistance.

Excessive voltage drop in a circuit can cause lights to flicker or burn dimly, heaters to heat poorly, and motors to run hotter than normal and burn out. This condition causes the load to work harder with less voltage pushing the current.

Experts say that voltage drop should never be greater than 3 percent. This is done by selecting the right size of wire, and by taking care in the use of extension cords and similar devices.

There are four basic causes of voltage drop.

The first is the choice of material used for the wire. Copper is a better conductor than aluminum and will have less voltage drop than aluminum for a given length and wire size. The electricity that moves through a copper wire is actually a group of electrons being pushed by voltage. The higher the voltage, the more electrons that can be sent flowing through the wire.

Ampacity refers to the maximum number of electrons that can be pushed at one time – the word ampacity is short for ampere capacity.

Wire size is another important factor in determining voltage drop. Larger wire sizes (those with a greater diameter) will have less voltage drop than smaller wire sizes of the same length. In American wire gauge, every 6 gauge decrease gives a doubling of the wire diameter, and every 3 gauge decrease doubles the wire cross sectional area. 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.

Still another critical factor in voltage drop is wire length. Shorter wires will have less voltage drop than longer wires for the same wire size (diameter). Voltage drop becomes important when the length of a run of wire or cable becomes very long. Usually this is not a problem in circuits within a house, but may become an issue when running wire to an outbuilding, well pump, etc.

Excessive voltage drop can cause loss of efficiency in operation of light, motors and appliances. This could result in lights that are dim and motors or appliances whose life is shortened. So it is important to use the right gauge of wire when running wires for a long distance.

Finally, the amount of current being carried can affect voltage drop levels. Voltage drop increases on a wire with an increase in the current flowing through the wire. Current carrying capacity is the same as ampacity.

The ampacity of a wire depends on a number of factors. Wires are covered with insulation, and this can be damaged if the temperature of the wire becomes too high. The basic material from which the wire is made is, of course, an important limiting factor. If alternating current is being sent through the wire, the speed of alternation can affect ampacity. The temperature in which the wire is used can also affect ampacity.

Cables are often used in bundles, and when they are brought together, the total heat which they generate has an effect on ampacity and voltage drop. There are strict rules about bundling cables which must be followed for this reason.

Cable selection is guided by two main principles. First, the cable should be able to carry the current load imposed on it without overheating. It should be able to do this in the most extreme conditions of temperature it will encounter during its working life. Second, it should offer sufficiently sound earthing to (i) limit the voltage to which people are exposed to a safe level and (ii) allow the fault current to trip the fuse in a short time.

These are important safety considerations. During 2005-2009, there was an average of 373900 fires per year caused by poor electrical installations. Choosing the right cable for the job is a critical safety measure.