Question 1

What is an acceptable voltage drop?

Accepted Answer

NEC recommends ≤3% for branch circuits and ≤5% total (feeder + branch). Some equipment is more sensitive; motors may require ≤2% during starting. Check manufacturer specifications.

Question 2

What is the difference between AWG sizes?

Accepted Answer

AWG (American Wire Gauge) uses smaller numbers for larger wires. Each 3-gauge decrease roughly doubles the cross-sectional area and halves the resistance. AWG 12 is common for 20A circuits; AWG 10 for 30A.

Question 3

Should I use copper or aluminum?

Accepted Answer

Copper has lower resistance (~60% of aluminum) but costs more. Aluminum is common for larger feeders and service entrance. Aluminum requires larger sizes and proper terminations.

Question 4

Why use one-way length, not total?

Accepted Answer

The calculator applies the appropriate factor internally: ×2 for DC/single-phase (round trip) and ×√3 for three-phase. Enter the one-way distance from source to load.

Question 5

Does this account for power factor?

Accepted Answer

No, this simplified model uses DC resistance only. For long runs with inductive loads (motors), actual voltage drop may be higher due to reactance. Use a more detailed calculation for critical applications.

Question 6

How do I verify the wire will handle the current safely?

Accepted Answer

This calculator addresses voltage drop only. You must separately verify ampacity per NEC Table 310.16 (or local equivalent), considering insulation type, ambient temperature, and bundling.