Wire Gauge for 20A at 50 ft on 120V — NEC Calculator
For 20A at 50 ft on 120V, use 10 AWG copper. Voltage drop: 2.07%. Per NEC 2023 Table 310.16.
Advanced options — derating, breaker & conduit
10 AWGcopper
Ampacity OKVD 2.07%VD GOVERNS
Long run (50 ft) requires upsizing from 12 AWG to 10 AWG for voltage drop.
Ampacity30Aat 60°C
Voltage drop2.07%2.49V
At load117.5Vreceiving end
Circular mils10,3805.26 mm²
Min for ampacity
12 AWG
6,530 CM
Min for ≤3% VD ← governs
10 AWG
10,380 CM
⚠Long run (50 ft) governs — upsized from 12 AWG to 10 AWG for ≤3% VD.
Copper vs Aluminum (for 20A at 50 ft on 120V)
Copper
12 AWG
VD: 3.3% · 3.31 mm²
Aluminum
10 AWG
VD: 3.4% · 5.26 mm²
What wire gauge for 20A at 50 ft on 120V?
For a 20A circuit at 50 ft on 120V, use 10 AWG copper conductor.
At 50 ft, voltage drop is the governing constraint — 12 AWG meets ampacity alone, but the long run requires 10 AWG to stay within 3% voltage drop.
Recommended wire gauge
Voltage drop governs
10 AWG copper
30A ampacity | 2.07% VD | 117.5V at load
Minimum wire by constraint
Required CMs: 7,167 CM. Formula: CM = (2 × K × I × L) / (V × 3%)
Wire size by run distance
Distance sensitivity for 20A on 120V at 3% voltage-drop target.
Voltage drop by run distance
Visual Analysis1 series6 points
Interactive line view for 1 series and 6 sampled points, built for quick reading and clear comparison.
Trend
Upward
Min
1.65
Max
2.6
Insight
Voltage drop by run distance shows an upward pattern, with a visible peak around 100 ft at 2.6.X-axis: One-way distanceY-axis: Voltage drop (%)
Voltage drop by run distance
Copper vs aluminum for this run
Material comparison uses the same amps, voltage, distance, temperature rating, and voltage-drop limit.
Protection, conduit, cost, and loss planning
These planning values are generated from the recommended conductor and are not a substitute for field code review.
Sizing assumptions
Sizing uses copper conductor data, 60C ampacity, single-phase voltage drop, 3% maximum voltage drop, not more than 3 current-carrying conductors, and 30C ambient.
The recommended wire is the larger of the ampacity minimum and the voltage-drop minimum. Long runs can require upsizing even when ampacity alone passes.
Breaker sizing, equipment grounding conductor sizing, conduit estimate, power loss, and cost are computed from the recommended conductor for planning context.
Safety and code review notes
Use the equipment nameplate and local code as the final authority. HVAC, EVSE, motors, continuous loads, and feeders often have extra NEC rules beyond a simple amps-and-distance calculation.
Aluminum conductors require listed AL/CU terminations and installation practices appropriate to the conductor and environment.
This sizing has warnings: Long run (50 ft) governs — upsized from 12 AWG to 10 AWG for ≤3% VD.
Step-by-step wire sizing
Load: 20A at 120V (single-phase), 50 ft, copper at 60°C
Step 1 — Ampacity: find smallest wire where derated ampacity ≥ 20A → 12 AWG (base 20A, no derating)
Step 2 — Voltage drop: allowed VD = 120V × 3% = 3.5999999999999996V
CM = (2 × 12.9 × 20A × 50ft) / 3.5999999999999996V = 7,167 CM → 10 AWG
Step 3 — Recommended: 10 AWG (VD governs)
Breaker: NEC 240.6(A): use 20A breaker (next standard size ≥ 20A)
Ground wire: NEC Table 250.122: 20A OCPD → EGC ≥ 12 AWG Cu (or 10 AWG Al)
Power loss: 48W in run — ~420.5 kWh/yr (~$58.87/yr @ $0.14/kWh)
Cost: ~$0.72/ft × 100 ft = ~$72 (2024 retail THHN)
Conduit: minimum 3/4" EMT for 3 conductors of 10 AWG
Verification: 30A ≥ 20A ✓ | VD 2.07% ≤ 3% ✓
Wire sizing FAQ
Why did the calculator recommend 10 AWG?
10 AWG is needed because voltage drop governs this 50 ft run even though 12 AWG meets ampacity alone.
10 AWG is needed because voltage drop governs this 50 ft run even though 12 AWG meets ampacity alone.
Does voltage or amperage matter more?
Both matter. Amperage drives ampacity and heat, while voltage and distance drive the voltage-drop percentage seen at the load.
Both matter. Amperage drives ampacity and heat, while voltage and distance drive the voltage-drop percentage seen at the load.
Can aluminum be used instead of copper?
Aluminum may be valid only with AL-rated equipment and code-approved terminations. The material comparison table shows how the recommendation changes when material changes.
Aluminum may be valid only with AL-rated equipment and code-approved terminations. The material comparison table shows how the recommendation changes when material changes.
What should be checked before installation?
Confirm breaker size, terminal temperature, insulation type, conductor count, raceway fill, ambient conditions, and local code before treating the planning result as final.
Confirm breaker size, terminal temperature, insulation type, conductor count, raceway fill, ambient conditions, and local code before treating the planning result as final.