Voltage drop is the amount of voltage loss that occurs in either part or all of a circuit due to impedance. Voltage drops that are too low can result in poor performance of a product and can even damage electrical equipment if severe enough. While the National Electric Code (NEC) does not recognize voltage drop to be a safety issue, they do recommend limiting the voltage drop from the breaker box to the farthest outlet for lighting, heating and power to 3% of the circuit’s voltage. This is made possible by choosing the correct wire size. Using a voltage drop formula or voltage drop calculator can help you avoid the hassle and headache caused by choosing the wrong wiring material and sizing for your power needs.
The National Electrical Code says that a voltage drop of 5% at the furthest receptacle in a branch wiring circuit is passable for normal efficiency. For a 120-volt 15 ampere circuit, this means that there should be no greater than a 6 volt drop at the furthest outlet when the circuit is fully loaded. Use our dc voltage drop calculator above to make sure you are within an acceptable range.
There are four fundamental causes of voltage drop, including the material used, the wire size, wire length, and current being carried. Copper is known as being a better conductor than aluminum. Larger diameter wires will have less voltage drop than smaller diameter wires that run the same length. Wire length matters since shorter wires will have less voltage drop than longer ones. Lastly, a voltage drop increases with an increase in the current flowing through the wire.
To decrease or eliminate voltage drop you can increase the size of the conductor being used to carry power to your electrical load. The increased conductor size reduces the amount of resistance on the conductor and the overall resistance on the entire circuit.
In order to choose the right wire size you’ll need to use a voltage drop calculator, or know the voltage drop formula.