Wire Voltage Drop
Calculate power loss in cables.
Understanding Voltage Drop
Every wire has some internal resistance. When current flows through it, some voltage is lost as heat. This is Voltage Drop. If the drop is too high, your device might not receive enough power to operate correctly, or worse, the wire could melt and cause a fire.
This calculator determines the voltage loss based on wire gauge (AWG), length, and current load, helping you select the safe wire size for your project.
The Math Behind the Drop (Ohm's Law)
The calculation is a direct application of Ohm's Law (V = IR).
Vdrop = I × Rtotal
Rtotal = 2 × Length × (Resistivity / Area)
Why is Length Doubled?
Current flows from the source, to the load, and back to the source. A 10-meter cable actually has 20 meters of wire conducting current.
Standard Copper Resistance (approx @ 20°C):
- 10 AWG: ~3.28 mΩ/meter
- 14 AWG: ~8.29 mΩ/meter
- 24 AWG: ~84.2 mΩ/meter
Practical Applications
- Solar Panels: Long runs from roof to basement inverter. High voltage drop here means wasting free solar energy.
- Automotive: Wiring 12V amps or off-road lights. 12V systems are very sensitive to drop (1V loss is ~8% power loss!).
- PoE (Power over Ethernet): Ensuring security cameras at the end of long CAT6 runs get enough voltage.
FAQ
What is an acceptable voltage drop?
Standard NEC code suggests a max drop of 3% for critical loads (like lighting or electronics) and 5% for non-critical loads. For 12V systems, aim for <3%.< /p>
Copper vs Aluminum wire?
Aluminum has higher resistance than Copper (~1.6x higher). If you use Aluminum wire, you typically need to go up two gauges (e.g., use 6 AWG Aluminum to replace 8 AWG Copper).
Does AC vs DC matter?
For resistive voltage drop: No. Resistance is the same. However, for AC at very high frequencies or large gauges, "Skin Effect" and inductance can increase the effective impedance, but for standard house wiring (50/60Hz), the DC resistance formula is accurate enough.