5 Amp Wire Size at 40 Feet (120V Single-Phase (US Standard Branch))
Complete conductor sizing, Ohm's law voltage drop, $I^2R$ line power loss, and circuit breaker specification for a 5 A load over a 40 ft (12.2 m) one-way run.
Copper Wire (≤3% Drop)14 AWG2.08 mm² · Drop: 1.05%
Aluminum Wire (≤3% Drop)14 AWGDrop: 2.07V (1.72%)
Voltage at Load End118.7 VLoss: 1.25 V (6.3 W)
Power & Breaker (125%)0.6 kW10A Breaker Recommended
All AWG & kcmil Wire Gauges for 5 Amps at 40 Feet (120V)
| Wire Gauge | Metric Area | NEC 75°C Cu Ampacity | Copper Voltage Drop | Load Voltage | Aluminum Drop | Line Loss ($I^2R$) | NEC Status |
|---|---|---|---|---|---|---|---|
| 14 AWG | 2.08 mm² | 15 A | 1.25 V (1.05%) | 118.7 V | 2.07 V (1.72%) | 6.3 W | ✓ PASS (≤3%) |
| 12 AWG | 3.31 mm² | 20 A | 0.79 V (0.66%) | 119.2 V | 1.3 V (1.08%) | 3.9 W | ✓ PASS (≤3%) |
| 10 AWG | 5.26 mm² | 30 A | 0.5 V (0.41%) | 119.5 V | 0.82 V (0.68%) | 2.5 W | ✓ PASS (≤3%) |
| 8 AWG | 8.37 mm² | 50 A | 0.31 V (0.26%) | 119.7 V | 0.51 V (0.43%) | 1.6 W | ✓ PASS (≤3%) |
| 6 AWG | 13.3 mm² | 65 A | 0.2 V (0.16%) | 119.8 V | 0.32 V (0.27%) | 1.0 W | ✓ PASS (≤3%) |
| 4 AWG | 21.15 mm² | 85 A | 0.12 V (0.1%) | 119.9 V | 0.2 V (0.17%) | 0.6 W | ✓ PASS (≤3%) |
| 3 AWG | 26.67 mm² | 100 A | 0.1 V (0.08%) | 119.9 V | 0.16 V (0.13%) | 0.5 W | ✓ PASS (≤3%) |
| 2 AWG | 33.62 mm² | 115 A | 0.08 V (0.06%) | 119.9 V | 0.13 V (0.11%) | 0.4 W | ✓ PASS (≤3%) |
| 1 AWG | 42.41 mm² | 130 A | 0.06 V (0.05%) | 119.9 V | 0.1 V (0.08%) | 0.3 W | ✓ PASS (≤3%) |
| 1/0 AWG | 53.49 mm² | 150 A | 0.05 V (0.04%) | 120.0 V | 0.08 V (0.07%) | 0.2 W | ✓ PASS (≤3%) |
| 2/0 AWG | 67.43 mm² | 175 A | 0.04 V (0.03%) | 120.0 V | 0.06 V (0.05%) | 0.2 W | ✓ PASS (≤3%) |
| 3/0 AWG | 85.01 mm² | 200 A | 0.03 V (0.03%) | 120.0 V | 0.05 V (0.04%) | 0.2 W | ✓ PASS (≤3%) |
| 4/0 AWG | 107.2 mm² | 230 A | 0.02 V (0.02%) | 120.0 V | 0.04 V (0.03%) | 0.1 W | ✓ PASS (≤3%) |
| 250 kcmil | 126.7 mm² | 255 A | 0.02 V (0.02%) | 120.0 V | 0.03 V (0.03%) | 0.1 W | ✓ PASS (≤3%) |
| 300 kcmil | 152.0 mm² | 285 A | 0.02 V (0.01%) | 120.0 V | 0.03 V (0.02%) | 0.1 W | ✓ PASS (≤3%) |
| 350 kcmil | 177.3 mm² | 310 A | 0.01 V (0.01%) | 120.0 V | 0.02 V (0.02%) | 0.1 W | ✓ PASS (≤3%) |
| 400 kcmil | 202.7 mm² | 335 A | 0.01 V (0.01%) | 120.0 V | 0.02 V (0.02%) | 0.1 W | ✓ PASS (≤3%) |
| 500 kcmil | 253.4 mm² | 380 A | 0.01 V (0.01%) | 120.0 V | 0.02 V (0.01%) | 0.1 W | ✓ PASS (≤3%) |
| 600 kcmil | 304.0 mm² | 420 A | 0.01 V (0.01%) | 120.0 V | 0.01 V (0.01%) | 0.0 W | ✓ PASS (≤3%) |
| 750 kcmil | 380.0 mm² | 475 A | 0.01 V (0.01%) | 120.0 V | 0.01 V (0.01%) | 0.0 W | ✓ PASS (≤3%) |
| 1000 kcmil | 506.7 mm² | 545 A | 0.01 V (0.0%) | 120.0 V | 0.01 V (0.01%) | 0.0 W | ✓ PASS (≤3%) |
Frequently Asked Engineering Questions
What size copper wire do I need for 5 amps at 40 feet (120V)?
To stay within the NEC recommended 3% maximum voltage drop for a 5A load over 40 feet one-way at 120V (1-Phase), you need 14 AWG copper wire. This produces a voltage drop of 1.25V (1.05%) and delivers 118.7V at the load.
What size aluminum wire is required for 5 amps at 40 feet?
Using aluminum conductors (75°C rating), you should use 14 AWG to maintain voltage drop at 2.07V (1.72%).
What breaker size is needed for a 5A continuous load?
Under NEC 210.20(A), continuous loads require a circuit breaker rated at 125% of the continuous current (5A × 1.25 = 6.2A), which corresponds to a standard 10A circuit breaker.
Compare Other Distances & Amperages
5 Amp Wire Size by Distance (120V)
5A at 20 ft (120V)5A at 30 ft (120V)5A at 50 ft (120V)5A at 60 ft (120V)5A at 75 ft (120V)5A at 80 ft (120V)5A at 100 ft (120V)5A at 120 ft (120V)5A at 125 ft (120V)5A at 150 ft (120V)5A at 175 ft (120V)