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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/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

 

CALCULATION TABLE FOR AC 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 %