# Voltage Drop Calculator

This is a calculator for the estimation of the voltage drop of an electrical circuit. The "NEC data" tab calculates based on the resistance and reactance data from the National Electrical Code (NEC). The "Estimated resistance" tab calculates based on the resistance data estimated from the wire size. Click the "Other" tab to use customized resistance or impedance data, such as data from other standards or wire manufacturers.

## Result

Voltage drop: 2.92
Voltage drop percentage: 1.22%
Voltage at the end: 237.08

The calculation result above is based on alternating current resistance and reactance data of 3-phase, 60 Hz, 75°C from National Electrical Code (NEC). The actual voltage drop can vary depending on the condition of the wire, the temperature, the connector, the frequency etc.

 Wire material Copper Aluminum Wire size 14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 3 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG 250 kcmil 300 kcmil 350 kcmil 400 kcmil 500 kcmil 600 kcmil 750 kcmil 1000 kcmil Material of conduit PVC Aluminum Steel Power factor (PF)
 Wire material Copper Aluminum Silver Gold Wire size 600 kcmil 500 kcmil 400 kcmil 350 kcmil 300 kcmil 250 kcmil 4/0 AWG (212 kcmil) 3/0 AWG (168 kcmil) 2/0 AWG (133 kcmil) 1/0 AWG (106 kcmil) 1 AWG (83.7 kcmil) 2 AWG (66.4 kcmil) 3 AWG (52.6 kcmil) 4 AWG (41.7 kcmil) 5 AWG (33.1 kcmil) 6 AWG (26.3 kcmil) 7 AWG (20.8 kcmil) 8 AWG (16.5 kcmil) 9 AWG (13.1 kcmil) 10 AWG (10.4 kcmil) 11 AWG (8.23 kcmil) 12 AWG (6.53 kcmil) 13 AWG (5.18 kcmil) 14 AWG (4.11 kcmil) 15 AWG (3.26 kcmil) 16 AWG (2.58 kcmil) 17 AWG (2.05 kcmil) 18 AWG (1.62 kcmil) 19 AWG (1.29 kcmil) 20 AWG (1.02 kcmil) 21 AWG (0.810 kcmil) 22 AWG (0.642 kcmil) 23 AWG (0.509 kcmil) 24 AWG (0.404 kcmil) 25 AWG (0.320 kcmil) 26 AWG (0.254 kcmil) 27 AWG (0.202 kcmil) 28 AWG (0.160 kcmil) 29 AWG (0.127 kcmil) 30 AWG (0.101 kcmil) 31 AWG (0.0797 kcmil) 32 AWG (0.0632 kcmil) 33 AWG (0.0501 kcmil) 34 AWG (0.0398 kcmil) 35 AWG (0.0315 kcmil) 36 AWG (0.0250 kcmil) 37 AWG (0.0198 kcmil) 38 AWG (0.0157 kcmil) 39 AWG (0.0125 kcmil) 40 AWG (0.00989 kcmil)
 Wire impendence or resistance Ω/km Ω/m mΩ/m Ω/1000ft Ω/ft mΩ/ft
 Voltage Phase DC AC single phase AC 3-phase Number of conductors single set of conductors 2 conductors per phase in parallel 3 conductors per phase in parallel 4 conductors per phase in parallel 5 conductors per phase in parallel 6 conductors per phase in parallel 7 conductors per phase in parallel 8 conductors per phase in parallel 9 conductors per phase in parallel Distance (one-way) feet meters miles kilometers Load current Amps

When electrical current moves through a wire, it is pushed by electrical potential (voltage) and it needs to surpass a certain level of contrary pressure caused by the wire. The voltage drop is the amount of electrical potential (voltage) loss caused by the contrary pressure of the wire. If the current is alternating, such contrary 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 contrary pressure is called 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. It is recommended that the voltage drop should be less than 5% under a fully loaded condition. This can be achieved by selecting the right wire, and by taking care in the use of extension cords and similar devices.

There are four major causes of voltage drop:

The first is the choice of material used for the wire. Silver, copper, gold, and aluminum are among the metals with the best electrical conductivity. Copper and aluminum are the most common materials used for wires due to their relatively low price compared with silver and gold. Copper is a better conductor than aluminum and will have less voltage drop than aluminum for a given length and wire size.

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 doubles 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. 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.

Finally, the amount of current being carried can affect voltage drop levels; an increase in current through a wire results in an increased voltage drop. Current carrying capacity is often referred to as ampacity, which is the maximum number of electrons that can be pushed at one time – the word ampacity is short for ampere capacity.

The ampacity of a wire depends on a number of factors. 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.

### Voltage drop calculation

Ohm's Law is a very basic law for calculating voltage drop:

Vdrop = I·R

where:

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

The resistance of the wires is often measured and given as length-specific resistance, normally in the unit of ohms per kilometer or ohms per 1000 feet. Also, the wire is round-tripped. Therefore, the formula for a single-phase or direct current circuit becomes:

Vdrop = 2·I·R·L

The formula for a three-phase circuit becomes:

Vdrop = √3·I·R·L

where:

I: the current through the wire
R: the length-specific resistance of the wires
L: the one-way length

### Typical AWG wire sizes

American Wire Gauge (AWG) is a wire gauge system used predominantly in North America for the diameters of round, solid, non-ferrous, electrically conducting wire. The following is a list of typical AWG wires and their sizes:

 AWG Diameter Turns of wire Area Copper resistance inch mm per inch per cm kcmil mm2 Ω/km Ω/1000ft 0000 (4/0) 0.4600 11.684 2.17 0.856 212 107 0.1608 0.04901 000 (3/0) 0.4096 10.404 2.44 0.961 168 85.0 0.2028 0.06180 00 (2/0) 0.3648 9.266 2.74 1.08 133 67.4 0.2557 0.07793 0 (1/0) 0.3249 8.252 3.08 1.21 106 53.5 0.3224 0.09827 1 0.2893 7.348 3.46 1.36 83.7 42.4 0.4066 0.1239 2 0.2576 6.544 3.88 1.53 66.4 33.6 0.5127 0.1563 3 0.2294 5.827 4.36 1.72 52.6 26.7 0.6465 0.1970 4 0.2043 5.189 4.89 1.93 41.7 21.2 0.8152 0.2485 5 0.1819 4.621 5.50 2.16 33.1 16.8 1.028 0.3133 6 0.1620 4.115 6.17 2.43 26.3 13.3 1.296 0.3951 7 0.1443 3.665 6.93 2.73 20.8 10.5 1.634 0.4982 8 0.1285 3.264 7.78 3.06 16.5 8.37 2.061 0.6282 9 0.1144 2.906 8.74 3.44 13.1 6.63 2.599 0.7921 10 0.1019 2.588 9.81 3.86 10.4 5.26 3.277 0.9989 11 0.0907 2.305 11.0 4.34 8.23 4.17 4.132 1.260 12 0.0808 2.053 12.4 4.87 6.53 3.31 5.211 1.588 13 0.0720 1.828 13.9 5.47 5.18 2.62 6.571 2.003 14 0.0641 1.628 15.6 6.14 4.11 2.08 8.286 2.525 15 0.0571 1.450 17.5 6.90 3.26 1.65 10.45 3.184 16 0.0508 1.291 19.7 7.75 2.58 1.31 13.17 4.016 17 0.0453 1.150 22.1 8.70 2.05 1.04 16.61 5.064 18 0.0403 1.024 24.8 9.77 1.62 0.823 20.95 6.385 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 21 0.0285 0.723 35.1 13.8 0.810 0.410 42.00 12.80 22 0.0253 0.644 39.5 15.5 0.642 0.326 52.96 16.14 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 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 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 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 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