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# AC and DC Voltage Drop Calculator with Formulas and Examples

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Voltage drop calculator helps to find out the voltage drop of your conductor when the load connected to it and length of conductor is known. This calculator is based on NEC Standard (NEC 2017 chapter 9; Tables 8 & 9).

Type of system

VoltageL-N
V
Power Factor
(between 0 & 1)
Conductor Type
Size of Conductor (in AWG or KCMIL)
Length of Conductor (in feets)
Type of Conduit
%Voltage Drop
%
Formula for Voltage Drop Calculation
%Voltage Drop =
calculated voltage drop (in volts) / Voltage (in volts)
x 100

## What is Voltage Drop?

Conductors carrying current always have inherent resistance, or impedance, to current flow. Power chord or chord set voltage drop is defined as the amount of voltage loss that occurs between the cordโs connection to a power source and the equipment it is supplying the power to on the opposite end.

It is essential to determine voltage drop because it may cause Loss of power to equipment, damage to the cables/conductors and violation of standard regulations that need to be followed. NEC 210.19 states the voltage drop values to not exceed 5% (feeder and branch circuits combined).

%Voltage Drop =
calculated voltage drop (in volts) / Voltage (in volts)
x 100
Impedance =
{Resistance x power factor} + {Reactance x sin(cos-1(power factor))}
AC Voltage Drop โ 1ฮฆ =
2 x Impedance x Load current (in amperes) x Length of conductor (in ft) / 1000
AC Voltage Drop โ 3ฮฆ =
โ3 x Impedance x Load current (in amperes) x Length of conductor (in ft) / 1000
DC Voltage Drop =
2 x Resistance x Load current (in amperes) x Length of conductor (in ft) / 1000

### When load is given in KVA:

load current (in amperes) โ 1ฮฆ =
load (in kVA) x 1000 / VoltageL-N (in volts)
load current (in amperes) โ 3ฮฆ =
load (in kVA) x 1000 / โ3 x VoltageL-L (in volts)

### When load is given in KWs:

load current (in amperes) โ 1ฮฆ =
load (in KWs)x 1000 / power factor x VoltageL-N
load current (in amperes) โ 3ฮฆ =
load (in KWs) x 1000 / โ3 x power factor x VoltageL-L
DC load current (in amperes) =
load (in KWs) x 1000 / Voltage

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### CALCULATION TABLE FOR DC CABLES

 SIZE (AWG/KCMIL) NUMBER OF STRANDS RESISTANCE IN OHM/KFT COPPER ALUMINIUM UNCOATED COATED ย 18 1 7.77 8.08 12.8 18 7 7.95 8.45 13.11 16 1 4.89 5.08 8.05 16 7 4.99 5.29 8.21 14 1 3.07 3.19 5.06 14 7 3.14 3.26 5.17 12 1 1.93 2.01 3.18 12 7 1.98 2.05 3.25 10 1 1.21 1.26 2 10 7 1.24 1.29 2.04 8 1 0.764 0.786 1.26 8 7 0.778 0.809 1.28 6 7 0.491 0.510 0.808 4 7 0.308 0.321 0.508 3 7 0.245 0.254 0.403 2 7 0.194 0.201 0.319 1 19 0.154 0.160 0.253 1/0 19 0.122 0.127 0.201 2/0 19 0.0967 0.101 0.159 3/0 19 0.0766 0.0797 0.126 4/0 19 0.0608 0.0626 0.1 250 37 0.0515 0.0535 0.0847 300 37 0.0429 0.0446 0.0707 350 37 0.0367 0.0382 0.0605 400 37 0.0321 0.0331 0.0529 500 37 0.0258 0.0265 0.0424 600 61 0.0214 0.0223 0.0353 700 61 0.0184 0.0189 0.0303 750 61 0.0171 0.0176 0.0282 800 61 0.0161 0.0166 0.0265 900 61 0.0143 0.0147 0.0235 1000 61 0.0129 0.0132 0.0212 1250 91 0.0103 0.0106 0.0169 1500 91 0.00858 0.00883 0.0141 1750 127 0.00735 0.00756 0.0121 2000 127 0.00643 0.00662 0.0106

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### CALCULATION TABLE FOR AC CABLES

 ย  SIZE (AWG OR KCMIL)ย XL (REACTANCE) FOR ALL WIRES *COPPER* XL (REACTANCE) FOR ALL WIRES *ALUMINIUM* PVC CONDUITS ALUMINUM CONDUITS STEEL CONDUIT PVC CONDUITS ALUMINUM CONDUITS STEEL CONDUIT 14 0.058 0.058 0.073 0.058 0.058 0.073 12 0.054 0.054 0.068 0.054 0.054 0.068 10 0.050 0.050 0.063 0.050 0.050 0.063 8 0.052 0.052 0.065 0.052 0.052 0.065 6 0.051 0.051 0.051 0.051 0.051 0.051 4 0.048 0.048 0.060 0.048 0.048 0.060 3 0.047 0.047 0.059 0.047 0.047 0.059 2 0.045 0.045 0.057 0.045 0.045 0.057 1 0.046 0.046 0.057 0.046 0.046 0.057 1/0 0.044 0.044 0.055 0.044 0.044 0.055 2/0 0.043 0.043 0.054 0.043 0.043 0.054 3/0 0.042 0.042 0.052 0.042 0.042 0.052 4/0 0.041 0.041 0.051 0.041 0.041 0.051 250 0.041 0.041 0.052 0.041 0.041 0.052 300 0.041 0.041 0.051 0.041 0.041 0.051 350 0.040 0.040 0.050 0.040 0.040 0.050 400 0.040 0.040 0.049 0.040 0.040 0.049 500 0.039 0.039 0.048 0.039 0.039 0.048 600 0.039 0.039 0.048 0.039 0.039 0.048 750 0.038 0.038 0.048 0.038 0.038 0.048 1000 0.037 0.037 0.046 0.037 0.037 0.046

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 SIZE (AWG OR KCMIL)ย ALTERNATING-CURRENT RESISTANCE FOR UNCOATED COPPER WIRES ALTERNATING-CURRENT RESISTANCE FOR ALUMINUM WIRES PVC CONDUIT ALUMINUM CONDUIT STEEL CONDUIT PVC CONDUIT ALUMINUM CONDUIT STEEL CONDUIT 14 3.100 3.100 3.100 โ โ โ 12 2.000 2.000 2.000 3.200 3.200 3.200 10 1.200 1.200 1.200 2.000 2.000 2.000 8 0.780 0.780 0.780 1.300 1.300 1.300 6 0.490 0.490 0.490 0.490 0.810 0.810 4 0.310 0.310 0.310 0.510 0.510 0.510 3 0.250 0.250 0.250 0.400 0.410 0.400 2 0.190 0.200 0.200 0.320 0.320 0.320 1 0.150 0.160 0.160 0.250 0.260 0.250 1/0 0.120 0.130 0.120 0.200 0.210 0.200 2/0 0.100 0.100 0.100 0.160 0.160 0.160 3/0 0.077 0.082 0.079 0.130 0.130 0.130 4/0 0.062 0.067 0.063 0.100 0.110 0.100 250 0.052 0.057 0.054 0.085 0.090 0.086 300 0.044 0.049 0.045 0.071 0.076 0.072 350 0.038 0.043 0.039 0.061 0.066 0.063 400 0.033 0.038 0.035 0.054 0.059 0.055 500 0.027 0.032 0.029 0.043 0.048 0.045 600 0.023 0.028 0.025 0.036 0.041 0.038 750 0.019 0.024 0.021 0.029 0.034 0.031 1000 0.015 0.019 0.018 0.023 0.027 0.025

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### SOLVED EXAMPLES

1. When type of system is 1-phase AC

Given:

Voltage = 120 V

Power factor = 0.85

Conductor type = AL

Size of conductor (in AWG or KCmil) = 3/0

Length of conductor (in ft) = 100 ft

Type of conduit = PVC

Required:

Voltage Drop = ?

%Voltage Drop = ?

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FOR VALUE OF X (REACTANCE)

 ย  SIZE (AWG OR KCMIL)ย XL (REACTANCE) FOR ALL WIRES *COPPER* XL (REACTANCE) FOR ALL WIRES *ALUMINIUM* PVC CONDUITS ALUMINUM CONDUITS STEEL CONDUIT PVC CONDUITS ALUMINUM CONDUITS STEEL CONDUIT 14 0.058 0.058 0.073 0.058 0.058 0.073 12 0.054 0.054 0.068 0.054 0.054 0.068 10 0.050 0.050 0.063 0.050 0.050 0.063 8 0.052 0.052 0.065 0.052 0.052 0.065 6 0.051 0.051 0.051 0.051 0.051 0.051 4 0.048 0.048 0.060 0.048 0.048 0.060 3 0.047 0.047 0.059 0.047 0.047 0.059 2 0.045 0.045 0.057 0.045 0.045 0.057 1 0.046 0.046 0.057 0.046 0.046 0.057 1/0 0.044 0.044 0.055 0.044 0.044 0.055 2/0 0.043 0.043 0.054 0.043 0.043 0.054 3/0 0.042 0.042 0.052 0.042 0.042 0.052 4/0 0.041 0.041 0.051 0.041 0.041 0.051 250 0.041 0.041 0.052 0.041 0.041 0.052 300 0.041 0.041 0.051 0.041 0.041 0.051 350 0.040 0.040 0.050 0.040 0.040 0.050 400 0.040 0.040 0.049 0.040 0.040 0.049 500 0.039 0.039 0.048 0.039 0.039 0.048 600 0.039 0.039 0.048 0.039 0.039 0.048 750 0.038 0.038 0.048 0.038 0.038 0.048 1000 0.037 0.037 0.046 0.037 0.037 0.046

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FOR VALUE OF R (RESISTANCE)

 SIZE (AWG OR KCMIL)ย ALTERNATING-CURRENT RESISTANCE FOR UNCOATED COPPER WIRES ALTERNATING-CURRENT RESISTANCE FOR ALUMINUM WIRES PVC CONDUIT ALUMINUM CONDUIT STEEL CONDUIT PVC CONDUIT ALUMINUM CONDUIT STEEL CONDUIT 14 3.100 3.100 3.100 โ โ โ 12 2.000 2.000 2.000 3.200 3.200 3.200 10 1.200 1.200 1.200 2.000 2.000 2.000 8 0.780 0.780 0.780 1.300 1.300 1.300 6 0.490 0.490 0.490 0.490 0.810 0.810 4 0.310 0.310 0.310 0.510 0.510 0.510 3 0.250 0.250 0.250 0.400 0.410 0.400 2 0.190 0.200 0.200 0.320 0.320 0.320 1 0.150 0.160 0.160 0.250 0.260 0.250 1/0 0.120 0.130 0.120 0.200 0.210 0.200 2/0 0.100 0.100 0.100 0.160 0.160 0.160 3/0 0.077 0.082 0.079 0.130 0.130 0.130 4/0 0.062 0.067 0.063 0.100 0.110 0.100 250 0.052 0.057 0.054 0.085 0.090 0.086 300 0.044 0.049 0.045 0.071 0.076 0.072 350 0.038 0.043 0.039 0.061 0.066 0.063 400 0.033 0.038 0.035 0.054 0.059 0.055 500 0.027 0.032 0.029 0.043 0.048 0.045 600 0.023 0.028 0.025 0.036 0.041 0.038 750 0.019 0.024 0.021 0.029 0.034 0.031 1000 0.015 0.019 0.018 0.023 0.027 0.025

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Solution:

From the tables we get values of resistance and reactance corresponding the conductor data:

Resistance = 0.13 โฆ/1000ft

Reactance = 0.042 โฆ/1000ft

Impedance = {0.13 ร 0.85} + {0.042 ร sinโก (cos-1โก(0.85))}

Impedance = 0.1326 โฆ/1000ft

AC Voltage Drop โ 1ฮฆ =
2 x 0.1326 x 225 x 100 / 1000

AC Voltage Drop โ 1ฮฆ = 5.967 volts

%Voltage Drop =
5.967 / 120
x 100

%Voltage Drop = 4.973 %

2. When type of system is 3-phase AC

Given:

Voltage = 480 V

Power factor = 1

Conductor type = Cu

Size of conductor (in AWG or KCmil) = 3/0

Length of conductor (in ft) = 600 ft

Type of conduit = Steel

Required:

Voltage Drop = ?

%Voltage Drop = ?

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FOR VALUE OF X (REACTANCE)

 ย  SIZE (AWG OR KCMIL)ย XL (REACTANCE) FOR ALL WIRES *COPPER* XL (REACTANCE) FOR ALL WIRES *ALUMINIUM* PVC CONDUITS ALUMINUM CONDUITS STEEL CONDUIT PVC CONDUITS ALUMINUM CONDUITS STEEL CONDUIT 14 0.058 0.058 0.073 0.058 0.058 0.073 12 0.054 0.054 0.068 0.054 0.054 0.068 10 0.050 0.050 0.063 0.050 0.050 0.063 8 0.052 0.052 0.065 0.052 0.052 0.065 6 0.051 0.051 0.051 0.051 0.051 0.051 4 0.048 0.048 0.060 0.048 0.048 0.060 3 0.047 0.047 0.059 0.047 0.047 0.059 2 0.045 0.045 0.057 0.045 0.045 0.057 1 0.046 0.046 0.057 0.046 0.046 0.057 1/0 0.044 0.044 0.055 0.044 0.044 0.055 2/0 0.043 0.043 0.054 0.043 0.043 0.054 3/0 0.042 0.042 0.052 0.042 0.042 0.052 4/0 0.041 0.041 0.051 0.041 0.041 0.051 250 0.041 0.041 0.052 0.041 0.041 0.052 300 0.041 0.041 0.051 0.041 0.041 0.051 350 0.040 0.040 0.050 0.040 0.040 0.050 400 0.040 0.040 0.049 0.040 0.040 0.049 500 0.039 0.039 0.048 0.039 0.039 0.048 600 0.039 0.039 0.048 0.039 0.039 0.048 750 0.038 0.038 0.048 0.038 0.038 0.048 1000 0.037 0.037 0.046 0.037 0.037 0.046

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FOR VALUE OF R (RESISTANCE)

 SIZE (AWG OR KCMIL)ย ALTERNATING-CURRENT RESISTANCE FOR UNCOATED COPPER WIRES ALTERNATING-CURRENT RESISTANCE FOR ALUMINUM WIRES PVC CONDUIT ALUMINUM CONDUIT STEEL CONDUIT PVC CONDUIT ALUMINUM CONDUIT STEEL CONDUIT 14 3.100 3.100 3.100 โ โ โ 12 2.000 2.000 2.000 3.200 3.200 3.200 10 1.200 1.200 1.200 2.000 2.000 2.000 8 0.780 0.780 0.780 1.300 1.300 1.300 6 0.490 0.490 0.490 0.490 0.810 0.810 4 0.310 0.310 0.310 0.510 0.510 0.510 3 0.250 0.250 0.250 0.400 0.410 0.400 2 0.190 0.200 0.200 0.320 0.320 0.320 1 0.150 0.160 0.160 0.250 0.260 0.250 1/0 0.120 0.130 0.120 0.200 0.210 0.200 2/0 0.100 0.100 0.100 0.160 0.160 0.160 3/0 0.077 0.082 0.079 0.130 0.130 0.130 4/0 0.062 0.067 0.063 0.100 0.110 0.100 250 0.052 0.057 0.054 0.085 0.090 0.086 300 0.044 0.049 0.045 0.071 0.076 0.072 350 0.038 0.043 0.039 0.061 0.066 0.063 400 0.033 0.038 0.035 0.054 0.059 0.055 500 0.027 0.032 0.029 0.043 0.048 0.045 600 0.023 0.028 0.025 0.036 0.041 0.038 750 0.019 0.024 0.021 0.029 0.034 0.031 1000 0.015 0.019 0.018 0.023 0.027 0.025

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Solution:

From the tables we get values of resistance and reactance corresponding the conductor data:

Resistance = 0.079 โฆ/1000ft

Reactance = 0.052 โฆ/1000ft

Impedance = {0.079 ร 1} + {0.052 ร sinโก (cos-1โก(1))}

Impedance = 0.079 โฆ/1000ft

AC Voltage Drop โ 3ฮฆ =
โ3 x 0.079 x 225 x 600 / 1000

AC Voltage Drop โ 3ฮฆ = 18.47 volts

%Voltage Drop =
18.47 / 480
x 100

%Voltage Drop = 3.85 %

3. When type of system is DC

Given:

Voltage = 120 V

Conductor type = Coated Cu

Size of conductor (in AWG or KCmil) = 3/0

Length of conductor (in ft) = 60 ft

Required:

Voltage Drop = ?

%Voltage Drop = ?

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FOR VALUE OF R (RESISTANCE)

 SIZE (AWG/KCMIL) NUMBER OF STRANDS RESISTANCE IN OHM/KFT COPPER ALUMINIUM UNCOATED COATED ย 18 1 7.77 8.08 12.8 18 7 7.95 8.45 13.11 16 1 4.89 5.08 8.05 16 7 4.99 5.29 8.21 14 1 3.07 3.19 5.06 14 7 3.14 3.26 5.17 12 1 1.93 2.01 3.18 12 7 1.98 2.05 3.25 10 1 1.21 1.26 2 10 7 1.24 1.29 2.04 8 1 0.764 0.786 1.26 8 7 0.778 0.809 1.28 6 7 0.491 0.510 0.808 4 7 0.308 0.321 0.508 3 7 0.245 0.254 0.403 2 7 0.194 0.201 0.319 1 19 0.154 0.160 0.253 1/0 19 0.122 0.127 0.201 2/0 19 0.0967 0.101 0.159 3/0 19 0.0766 0.0797 0.126 4/0 19 0.0608 0.0626 0.1 250 37 0.0515 0.0535 0.0847 300 37 0.0429 0.0446 0.0707 350 37 0.0367 0.0382 0.0605 400 37 0.0321 0.0331 0.0529 500 37 0.0258 0.0265 0.0424 600 61 0.0214 0.0223 0.0353 700 61 0.0184 0.0189 0.0303 750 61 0.0171 0.0176 0.0282 800 61 0.0161 0.0166 0.0265 900 61 0.0143 0.0147 0.0235 1000 61 0.0129 0.0132 0.0212 1250 91 0.0103 0.0106 0.0169 1500 91 0.00858 0.00883 0.0141 1750 127 0.00735 0.00756 0.0121 2000 127 0.00643 0.00662 0.0106

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Solution:

From the table we get value of resistance corresponding the conductor data:

Resistance = 0.0797 โฆ/1000ft

DC Voltage Drop =
2 x 0.0797 x 25 x 60 / 1000

DC Voltage Drop = 0.2391 volts

%Voltage Drop =
0.2391 / 120
x 100

%Voltage Drop = 0.199 %

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