# Single Phase Voltage Drop Formula

The voltage drop formula for single phase systems is the following:

where:

**VD** = The voltage drop of the circuit, in volts.

**R** = The resistance of the conductor.

**I** = Amps.

**L** = Length of the circuit from power supply to load.

**CM** = Circular-Mils (conductor wire gauge)

**Notes**:

• The National Electric Code recommends a maximum 3% voltage drop for branch circuits. Voltage drop can be decreased by increasing the wire gauge, decreasing the load current, or decreasing the length between the power supply and the load.

• As a reference, a one circular mil, one foot long conductor has a resistance of 12.9 Ohms (copper) or 21.2 (aluminum) at an operating temperature of 75 C).

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