Calculate Your Voltage Drop & Optimise Your Electrical Design
This Voltage Drop Calculator implements the USA NEC Code. Voltage Drop Formulas are included below.
Obtain your voltage drop results by entering data in all fields.
Voltage Drop Calculator
Voltage drop calculation
Ohm’s Law is a basic law for calculating voltage drop:
Vdrop = I·R
where:
I: the current through the wire, measured in amperes (A)
R: the resistance of the wires, measured in ohms (Ω)
The resistance of the wires is often measured and given as length-specific resistance, normally in the unit of ohms per kilometre or ohms per 1000 feet. Also, the wire is round-tripped.
The formula for a single-phase or direct current circuit:
Vdrop = 2·I·R·L
The formula for a three-phase circuit:
Vdrop = √3·I·R·L
where:
I: the current (A) through the wire
R: the length-specific Resistance (R) of the wires
L: the one-way length (L)
Additional Information
The NEC recommends a maximum combined voltage drop of 5% for both feeder and branch circuits.
According to the NEC 210.19(A)(1) Informational Note No. 4, the voltage drop for branched circuits is limited to 3% of the applied voltage. This allows a 2% drop in the feeder.
In Europe, the maximum permitted voltage drop is 3% for lighting or 5% for other uses.
This is for low voltage installations supplied directly from a public LV distribution system.
For low voltage installations supplied from private LV Supply, the limits are 6% for lighting and 8% for other uses.
For Consumer’s Installations, the maximum permitted voltage drop is 3% for lighting or 5% for other uses.
This is for low voltage installations supplied directly from a public LV distribution system.
For low voltage installations supplied from private LV Supply, the limits are 6% for lighting and 8% for other uses.
For Commercial and Industrial Installations, the supply voltage can vary between statutory limits of +10% to –6%.
The maximum permissible voltage drop between the point of supply and any point of the installation is as follows: Any low voltage Electrical installation must not exceed 5% voltage drop and where a substation is located on-premises, must not exceed 7% voltage drop.
Voltage drop at consumer final sub-circuit should be kept at below 4% – Under normal conditions, the voltage drop at the terminals of any fixed current-using equipment such as switch socket outlet should not exceed 4% of the nominal voltage of the supply.
| 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 |
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Comply with Voltage Drop Requirements
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