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

Wire type:  
Resistivity: Ω·m
Wire diameter size:
Wire/cable length (one way):
Current type:
Voltage in volts: V
Current in amps: A
Voltage drop in volts: V
Percentage of voltage drop: %
Wire resistance: Ω

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.

AWGDiameterTurns of wireAreaCopper resistance
inchmmper inchper cmkcmilmm2Ω/kmΩ/1000ft
0000 (4/0)0.460011.6842.170.8562121070.16080.04901
000 (3/0)0.409610.4042.440.96116885.00.20280.06180
00 (2/0)0.36489.2662.741.0813367.40.25570.07793
0 (1/0)0.32498.2523.081.2110653.50.32240.09827
10.28937.3483.461.3683.742.40.40660.1239
20.25766.5443.881.5366.433.60.51270.1563
30.22945.8274.361.7252.626.70.64650.1970
40.20435.1894.891.9341.721.20.81520.2485
50.18194.6215.502.1633.116.81.0280.3133
60.16204.1156.172.4326.313.31.2960.3951
70.14433.6656.932.7320.810.51.6340.4982
80.12853.2647.783.0616.58.372.0610.6282
90.11442.9068.743.4413.16.632.5990.7921
100.10192.5889.813.8610.45.263.2770.9989
110.09072.30511.04.348.234.174.1321.260
120.08082.05312.44.876.533.315.2111.588
130.07201.82813.95.475.182.626.5712.003
140.06411.62815.66.144.112.088.2862.525
150.05711.45017.56.903.261.6510.453.184
160.05081.29119.77.752.581.3113.174.016
170.04531.15022.18.702.051.0416.615.064
180.04031.02424.89.771.620.82320.956.385
190.03590.91227.911.01.290.65326.428.051
200.03200.81231.312.31.020.51833.3110.15
210.02850.72335.113.80.8100.41042.0012.80
220.02530.64439.515.50.6420.32652.9616.14
230.02260.57344.317.40.5090.25866.7920.36
240.02010.51149.719.60.4040.20584.2225.67
250.01790.45555.922.00.3200.162106.232.37
260.01590.40562.724.70.2540.129133.940.81
270.01420.36170.427.70.2020.102168.951.47
280.01260.32179.131.10.1600.0810212.964.90
290.01130.28688.835.00.1270.0642268.581.84
300.01000.25599.739.30.1010.0509338.6103.2
310.008930.22711244.10.07970.0404426.9130.1
320.007950.20212649.50.06320.0320538.3164.1
330.007080.18014155.60.05010.0254678.8206.9
340.006300.16015962.40.03980.0201856.0260.9
350.005610.14317870.10.03150.01601079329.0
360.005000.12720078.70.02500.01271361414.8
370.004450.11322588.40.01980.01001716523.1
380.003970.10125299.30.01570.007972164659.6
390.003530.08972831110.01250.006322729831.8
400.003140.07993181250.009890.0050134411049

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2021201-AE-Voltage-Drop-Calculator-Page-02

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This results in a massive reduction of electrical power cables, enabling you to enjoy substantial cable cost savings – and complying to voltage drop requirements.

automatic voltage stabiliser

Comply with Voltage Drop Requirements

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