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

1-Phase AC System
3-Phase AC System
DC System

Voltage_L-N

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 / Voltage_L-N (in volts)

load current (in amperes) – 3Φ =

load (in kVA) x 1000 / √3 x Voltage_L-L (in volts)

When load is given in KWs:

load current (in amperes) – 1Φ =

load (in KWs)x 1000 / power factor x Voltage_L-N

load current (in amperes) – 3Φ =

load (in KWs) x 1000 / √3 x power factor x Voltage_L-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
SIZE (AWG OR KCMIL)	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
SIZE (AWG OR KCMIL)	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
SIZE (AWG OR KCMIL)	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
SIZE (AWG OR KCMIL)	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
SIZE (AWG OR KCMIL)	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
SIZE (AWG OR KCMIL)	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 %

AC and DC Voltage Drop Calculator with Formulas and Examples

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What is Voltage Drop?

When load is given in KVA:

When load is given in KWs:

CALCULATION TABLE FOR DC CABLES

CALCULATION TABLE FOR AC CABLES

SOLVED EXAMPLES

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