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AC and DC Voltage Drop Calculator with Formulas and Examples

 

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
Load Rating
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
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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 cord’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 – 1Φ =
2 x Impedance x Load current (in amperes) x Length of conductor (in ft) / 1000
AC Voltage Drop – 3Φ =
√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) – 1Φ =
load (in kVA) x 1000 / VoltageL-N (in volts)
load current (in amperes) – 3Φ =
load (in kVA) x 1000 / √3 x VoltageL-L (in volts)

When load is given in KWs:

load current (in amperes) – 1Φ =
load (in KWs)x 1000 / power factor x VoltageL-N
load current (in amperes) – 3Φ =
load (in KWs) x 1000 / √3 x power factor x VoltageL-L
DC load current (in amperes) =
load (in KWs) x 1000 / Voltage

 

CALCULATION TABLE FOR DC CABLES

SIZE (AWG OR KCMIL) 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

 

SIZE
(AWG
OR
KCMIL)		 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 — — —
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

SOLVED EXAMPLES

1. When type of system is 1-phase AC

Given:

Voltage = 120 V

Load rating = 225 A

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 = ?

FOR VALUE OF X (REACTANCE)

SIZE
(AWG
OR
KCMIL)		 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

 

FOR VALUE OF R (RESISTANCE)

SIZE
(AWG
OR
KCMIL)		 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 — — —
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

 

Solution:

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

Resistance = 0.13 Ω/1000ft

Reactance = 0.042 Ω/1000ft

Impedance = {0.13 × 0.85} + {0.042 × sin⁡ (cos-1⁡(0.85))}

Impedance = 0.1326 Ω/1000ft

AC Voltage Drop – 1Φ =
2 x 0.1326 x 225 x 100 / 1000

AC Voltage Drop – 1Φ = 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

Load rating = 225 A

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 = ?

 

FOR VALUE OF X (REACTANCE)

SIZE
(AWG
OR
KCMIL)		 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

 

FOR VALUE OF R (RESISTANCE)

SIZE
(AWG
OR
KCMIL)		 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 — — —
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

 

Solution:

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

Resistance = 0.079 Ω/1000ft

Reactance = 0.052 Ω/1000ft

Impedance = {0.079 × 1} + {0.052 × sin⁡ (cos-1⁡(1))}

Impedance = 0.079 Ω/1000ft

AC Voltage Drop – 3Φ =
√3 x 0.079 x 225 x 600 / 1000

AC Voltage Drop – 3Φ = 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

Load rating = 25 A

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 = ?

 

FOR VALUE OF R (RESISTANCE)

SIZE (AWG/KCMIL) NUMBER OF STRANDS RESISTANCE IN OHM/KFT
COPPER ALUMINIUM
UNCOATED COATED  
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

 

Solution:

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

Resistance = 0.0797 Ω/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 %