Voltage Loss Calculator

While a voltage drop calculator determines how many volts are lost between a panel and an appliance, a Voltage Loss Calculator answers a different que

Electrical

Load Current (Amps)

Current flowing through conductors

One-Way Distance (Feet)

Distance from source to load

Conductor Size (AWG)

Copper conductor gauge

Circuit Phase System

Single-phase loop vs three-phase conductors

Daily Operating Hours

h/day

Hours the circuit operates under load daily

Electricity Rate ($/kWh)

$/kWh

Cost of electricity from your utility bill

Formula & Methodology

Power Loss (W) = I² × Rtotal; Energy Lost (kWh/yr) = (Power Loss ÷ 1000) × Hours/day × 365; Cost Lost ($/yr) = Energy Lost × Tariff Rate

Electrical power dissipation in conductors follows Joule's heating law: Power Loss = I² × R. Because power loss scales with the square of the current, doubling the amperage quadruples the heat dissipation. Total conductor resistance is computed from the number of current-carrying conductors (2 for single-phase, 3 for three-phase) and distance. Multiplying wasted kilowatts by annual operating hours and your utility rate reveals the financial cost of undersized wiring.

Continuous Conductor Power Loss (I²R Heat)

86.9 W Power Lost

Overview

While a voltage drop calculator determines how many volts are lost between a panel and an appliance, a Voltage Loss Calculator answers a different question: how much energy (kWh) and money are wasted as heat inside your building's wiring? Whenever current flows through conductors, I²R resistance dissipates electric power directly into walls and conduits.

Safety Notice: Electrical power loss calculations are reference estimates for financial and thermal efficiency analysis. They do not constitute code compliance certifications or engineering guarantees. Always consult the National Electrical Code (NEC) and hire a licensed electrician to evaluate conductor thermal limits.

Worked Examples

15A Continuous Load over 100 Feet with 12 AWG at $0.16/kWh

Current: 15A, Distance: 100 ft, 12 AWG copper (1.93 Ω/kft), 8 hours/day, $0.16/kWh.

Total Conductor Resistance: 2 × (100 ÷ 1000) × 1.93 Ω = 0.386 Ω
Calculate I²: 15 A × 15 A = 225 A²
Calculate Power Dissipation: 225 A² × 0.386 Ω = 86.85 W
Convert to Kilowatts: 86.85 ÷ 1000 = 0.08685 kW
Calculate Daily Energy Lost: 0.08685 kW × 8 h = 0.6948 kWh/day
Calculate Annual Energy Lost: 0.6948 × 365 = 253.6 kWh/year
Calculate Annual Cost: 253.6 kWh × $0.16 = $40.58 / year

Final Answer: 86.9 W Lost | 253.6 kWh/yr wasted ($40.58/year lost)

Heavy 30A RV Feeder over 150 Feet with 10 AWG Copper

Current: 30A, Distance: 150 ft, 10 AWG copper (1.21 Ω/kft), 12 hours/day, $0.20/kWh.

Resistance: 2 × 0.150 × 1.21 = 0.363 Ω
Power Loss: 30² × 0.363 = 900 × 0.363 = 326.7 W
Daily Energy: (326.7 ÷ 1000) × 12 = 3.92 kWh/day
Annual Cost: 3.92 × 365 × $0.20 = $286.16 / year

Final Answer: 326.7 W Lost | $286.16/year wasted

Three-Phase 20A Industrial Line over 200 Feet with 8 AWG

Current: 20A, Distance: 200 ft, 8 AWG copper (0.764 Ω/kft), Three-phase (3 wires), 24 h/day, $0.12/kWh.

Total Resistance (3 wires): 3 × 0.200 × 0.764 = 0.4584 Ω
Power Loss: 20² × 0.4584 = 400 × 0.4584 = 183.36 W
Annual Cost: (0.18336 × 24 × 365) × $0.12 = 1606.2 kWh × $0.12 = $192.75 / year

Final Answer: 183.4 W Lost | $192.75/year wasted

How to Use This Calculator

Enter the design current in amperes flowing through the circuit.

Enter the one-way distance in feet from panel to load.

Select the copper wire gauge (AWG) and phase configuration.

Enter daily operating hours and your local electricity rate per kWh.

Click Calculate to see the continuous wattage lost as heat and annual cost.

Reference Table

Wire Gauge (AWG)	Resistance (200 ft loop)	Loss at 10 Amps	Loss at 20 Amps	Loss at 30 Amps
14 AWG	0.614 Ω	61.4 W	245.6 W	Not Recommended (Exceeds ampacity)
12 AWG	0.386 Ω	38.6 W	154.4 W	Not Recommended (Exceeds ampacity)
10 AWG	0.242 Ω	24.2 W	96.8 W	217.8 W
8 AWG	0.153 Ω	15.3 W	61.2 W	137.7 W
6 AWG	0.098 Ω	9.8 W	39.2 W	88.2 W

Frequently Asked Questions

What is the difference between voltage drop and voltage loss?

Voltage drop measures the reduction in electrical potential (volts) delivered to an appliance. Voltage loss (or conductor power loss) measures the actual energy (watts and kWh) dissipated as waste heat through wire resistance, and the financial cost on your electric bill.

Why does doubling the current quadruple the power loss?

Because power loss follows Joule’s law: P = I² × R. Power depends on current squared. Increasing current from 10A to 20A increases power dissipation by a factor of (20/10)² = 4 times.

Can upsizing wire gauge pay for itself over time?

Yes. In continuous commercial loads (like data centers, continuous pumps, or commercial lighting), stepping up from 12 AWG to 10 AWG reduces resistance by ~37%. The annual electricity savings often pay for the thicker copper within 2 to 4 years.

Does wire heat dissipation pose a fire hazard?

Excessive I²R heat in undersized or tightly bundled wires can degrade insulation and create a fire hazard. Electrical codes establish maximum allowable ampacities and conduit fill rules to keep wire temperatures below insulation ratings.

How do I find my electricity rate per kWh?

Check your most recent electric utility bill. Divide your total monthly charges by the total kilowatt-hours (kWh) consumed to determine your effective all-inclusive rate per kWh (typically $0.12 to $0.28 in the United States).