What causes voltage drop?
Electrical conductors have resistance. When current flows through that resistance, part of the source voltage is dropped along the conductor.
Why wire length matters
Resistance increases with conductor length. In a two-conductor circuit, calculations normally account for the complete current path rather than only the one-way distance.
Why conductor size matters
Larger conductors generally have lower resistance than smaller conductors of the same material and length. Lower resistance reduces voltage drop for a given current.
Calculate voltage-drop percentage
Voltage-drop percentage expresses the lost voltage as a percentage of the source voltage.
Example
If a 120-volt circuit experiences a 3-volt drop, the voltage-drop percentage is 2.5 percent.
Factors that affect voltage drop
- Current flowing through the circuit
- Conductor length
- Conductor cross-sectional area
- Conductor material
- Operating temperature
- AC circuit impedance and power factor where applicable
Why voltage drop matters
Excessive voltage drop can reduce the voltage available to equipment and may affect performance. It is therefore considered when designing longer circuits and circuits carrying significant loads.
A simplified voltage-drop estimate is useful for planning, but final conductor selection should follow the applicable electrical code, equipment requirements and installation conditions.