What is the formula for single-phase and three-phase electrical voltage drop?

For single-phase circuits, Voltage Drop (VD) = (2 × K × I × D) / CM, and for three-phase circuits, VD = (1.732 × K × I × D) / CM, where K is conductor resistivity (12.9 for Copper, 21.2 for Aluminum at 75°C), I is current in amps, D is one-way distance in feet, and CM is the conductor cross-sectional area in Circular Mils.

What is the maximum allowable voltage drop under the Canadian Electrical Code (CEC)?

Under Canadian Electrical Code (CEC) Rule 8-102, voltage drop in a feeder or branch circuit should not exceed 3% of nominal supply voltage, and total voltage drop from the service point to the point of utilization should not exceed 5%.

Back to All Free ToolsBuildric Utility · Electrical · CEC / NEC 3% Branch Check

Free Voltage Drop Calculator Canada — Wire Size & Distance

Calculate exact voltage drop (V and %), terminal load voltage, and minimum recommended wire gauge (AWG / kcmil) for Canadian 120V, 208V, 240V, 347V, and 600V Copper or Aluminum circuits.

1. Circuit Voltage, Load, Wire Size & Length

System Voltage (V)

Circuit Phase

Load Current (Amps)

One-Way Distance (ft)

Distance Unit

Conductor Material

Wire Size (AWG / kcmil)

Power Factor (PF)

Transparent Voltage Drop Formula (75°C Reference):

• Formula: VD = (2 × K × I × D_ft) / CM

• Calculation: (2 × 12.9 × 30A × 125.0 ft) / 10,380 CM = 9.32V (3.88%)

ELECTRICAL VOLTAGE DROP CALCULATION SHEET

Bow River Electrical & Controls Ltd.

Panel B → Sub-Panel Garage / EV Charger (30A)

EXCEEDS 3.0% BRANCH LIMIT

PF: 0.9 · Copper (10 AWG)

% Voltage Drop3.88%(9.32 V drop)

Voltage at Load230.7 V(Source: 240V 1Φ)

Min Wire for ≤3% Drop8 AWG(Copper)

Conductor Size & Circular Mils (CM)	10 AWG (10,380 CM)
One-Way Run Length	125.0 ft (38.1 m)
Resistivity Constant (K at 75°C)	12.9 Ω·CM/ft (Cu)
Max One-Way Distance for 10 AWG to Stay ≤ 3.0%	97 ft (29.4 m)

CEC Rule 8-102 / NEC Guidance: Voltage drop in a branch circuit or feeder should not exceed 3.0% at the farthest outlet, and total voltage drop across combined feeder + branch circuit should not exceed 5.0% of nominal supply voltage.

Generated by Alberta Studio — Free Tools · albertastudio.devVerify ampacity & derating per Canadian Electrical Code

Export Voltage Drop Calculation Sheet (PDF)

Save for electrical permit submittals or panel schedules.

Automated Lead Capture & Quoting for Electricians

Want your service calls, EV charger quotes, and panel upgrades booked automatically? Check out Buildric.

Buildric answers missed calls via instant SMS and 24/7 AI voice reception while you are working in a panel, and organizes all your estimates in one CRM.

Explore Buildric for Electricians Book 15-Min Walkthrough

Electrical Code Disclaimer: For informational and preliminary calculation purposes only. Always verify wire ampacity, conduit fill, ambient temperature derating, and termination ratings (60°C/75°C/90°C) against the current Canadian Electrical Code (CEC Part I) and local inspection authority.