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.
30A
Ampacity
at 60°C
2.07%
Voltage drop
2.49V
117.5V
At load
receiving end
10,380
Circular mils
5.26 mm²
Min for ampacity
12 AWG
6,530 CM
Min for ≤3% VD ← governs
10 AWG
10,380 CM
20A
Breaker size
NEC 240.6(A)
~$72
Wire cost est.
100 ft THHN
3/4" EMT
Conduit size
3 conductors
12 AWG Cu
Ground wire (EGC)
NEC 250.122
48W
Power loss
~$58.87/yr
⚠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.
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% ✓