Long runs waste voltage, and motors and lights suffer for it. Enter the wire, load and distance to see the drop in volts and percent.
How it works
Uses 2 × K × amps × one-way length ÷ circular mils for single phase and 1.732 in place of 2 for three phase. K is 12.9 for copper and 21.2 for aluminum, with circular mils from the electrical code Chapter 9 Table 8.
Before you order
- Use one-way distance. The formula already counts the return path.
- Code guidance suggests about 3% on a branch circuit and 5% total including the feeder.
- If the drop is high, step up one wire size and check that it still fits the conduit.
Common questions
Is 3% voltage drop a code requirement?
In most editions it is an informational recommendation, not a rule. Local amendments and equipment makers can be stricter, so check before relying on it.
Does this account for power factor?
No. The simplified K method works well for short residential runs. Long feeders and motor loads need a calculation that includes reactance.