Calculators · Electrician
Metric Voltage Drop Calculator
Short answer
Voltage drop is current times the resistance of the conductors carrying it. For a two-wire single-phase circuit, Vd = 2 × I × R × L; for a balanced three-phase circuit, Vd = √3 × I × R × L, where R is the conductor resistance per metre and L is the one-way length. Compare the percent drop with the limit in the Canadian Electrical Code edition your province uses.
- Voltage drop
- 4.75 V
- Percent drop
- 1.98 %
- Voltage at load
- 235.2 V
Formula
Vd = k × I × (Ω/km × L ÷ 1000), k = 2 (1-phase) or √3 (3-phase)
Worked example
24 A over 30 m of conductor at 3.3 Ω/km on a 240 V single-phase circuit: R per conductor = 3.3 × 30 ÷ 1000 = 0.099 Ω, Vd = 2 × 24 × 0.099 = 4.75 V, or about 1.98 %.
Before you rely on it
- Use the conductor resistance from the CEC tables or the manufacturer's data for the size, material and temperature you are working with. This tool does not pick a conductor size for you.
- Percent-drop limits are set by the Canadian Electrical Code. Check the edition your province has adopted.
Studying for the Red Seal Electrician (309A) exam? Try 30 free practice questions or read the exam guide.