Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

# Electric Circuits Voltage Drop

## Ohm's law and voltage drop in electric circuits.

Voltage drop in an electric circuit can be calculated using Ohm's law as

U = R I                (1)

where

U = voltage drop (volts, V)

R = electrical resistance in the electric circuit (ohms, Ω)

I = current (amps, A)

### Example - Voltage Drop

Voltage drop in a 100 ft power line:

The electric resistance in the circuit can be calculated

R = (1.02 Ω/1000 ft) (100 ft) 2

= 0.204 Ω

The voltage drop in the circuit can be calculated with (1)

U = (0.204 Ω) (10 amps)

= 2.04 volts

### Circular mils and Voltage drop

Voltage drop can also be calculated using mils like

U = K P L I / A                       (2)

where

K = specific resistivity (Ω - circular mils/foot)

P = phase constant = 2 (for single phase) = 1.732 (for three phase)

L =  wire length (ft)

A = wire area (circular mils)

Specific electric resistivity for different types of wire materials

• Solid Copper, K = 11 (temp 77oF - 121oF), K = 12 (temp 122oF - 167oF)
• Solid Aluminum, K = 18 (temp 77oF - 121oF), K = 20 (temp 122oF - 167oF)
• Stranded Copper, K = 11 (temp 77oF - 121oF), K = 12 (temp 122oF - 167oF)
• Stranded Aluminum, K = 19 (temp 77oF - 121oF), K = 20 (temp 122oF - 167oF)

### Example - Specific resistivity and Voltage Drop

With values from the example above the voltage drop can be calculated as

U = (11 ohm - circular mils/foot) 2 (100 ft) (10 A) / (10400 mils)

= 2.11 V

### Copper Conductor - Voltage Drop Table

The voltage drop in a copper conductor can be estimated with

U = f I L                          (3)

where

f = factor from table below

I = current (amps)

L = conductor length (ft)

Copper Conductor - Voltage Drop
SizeFactor
- f -
AWGMetric
mm2
Single-phase3-phase
14 2.08 0.476 0.42
12 3.31 0.313 0.26
10 5.26 0.196 0.17
8 8.37 0.125 0.11
6 13.3 0.0833 0.071
4 21.2 0.0538 0.046
3 0.0431 0.038
2 33.6 0.0323 0.028
1 42.4 0.0323 0.028
1/0 53.5 0.0269 0.023
2/0 67.4 0.0222 0.020
3/0 85.0 0.019 0.016
4/0 107.2 0.0161 0.014
250 0.0147 0.013
300 0.0131 0.011
350 0.0121 0.011
400 0.0115 0.009
500 0.0101 0.009

## Related Topics

• ### Electrical

Electrical units, amps and electrical wiring, wire gauge and AWG, electrical formulas and motors.

## Related Documents

• ### Copper Wire - Electrical Resistance vs. Gauge

Gauge, weight, circular mils and electrical resistance in copper wire.
• ### Electric Circuit Diagram - Drawing Template

Online shareable electric circuit diagram.
• ### Electric Wire - Calculating Cross-Section Areas

Calculate single and bunched electric wire cross-section area and diameter.
• ### Electric Wire - Maximum Length with 240 Volts Single-Phase Power

Maximum length of 240 V single phase electric wire with max. 2% voltage drop.
• ### Electrical Motors - Maximum Cable Size and Length vs. Power

Maximum electrical motor cable length vs. power.
• ### Electrical Voltage and Frequency Standards by Country

Typical voltages and frequencies used for domestic appliances in different countries.
• ### Ohm's Law

The relation between voltage, current and electrical resistance.
• ### Relative vs. Absolute Voltage

Electric circuits and voltage at any point.

## Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

We don't collect information from our users. More about

## Citation

• The Engineering ToolBox (2009). Electric Circuits Voltage Drop. [online] Available at: https://www.engineeringtoolbox.com/voltage-drop-d_1550.html [Accessed Day Month Year].

Modify the access date according your visit.

9.29.12