Wire Gauge for 30A at 25 ft on 240V — NEC Calculator
For 30A at 25 ft on 240V, use 10 AWG copper. Voltage drop: 0.78%. Per NEC 2023 Table 310.16.
Advanced options — derating, breaker & conduit
10 AWGcopper
Ampacity OKVD 0.78%
10 AWG selected by ampacity (30A ≥ 30A).
Ampacity30Aat 60°C
Voltage drop0.78%1.86V
At load238.1Vreceiving end
Circular mils10,3805.26 mm²
Min for ampacity ← governs
10 AWG
10,380 CM
Min for ≤3% VD
14 AWG
4,110 CM
Copper vs Aluminum (for 30A at 25 ft on 240V)
Copper
10 AWG
VD: 0.8% · 5.26 mm²
Aluminum
8 AWG
VD: 0.8% · 8.37 mm²
What wire gauge for 30A at 25 ft on 240V?
For a 30A circuit at 25 ft on 240V, use 10 AWG copper conductor.
10 AWG (30A ampacity) satisfies both the 30A load and 3% voltage drop limit at 25 ft.
Recommended wire gauge
Ampacity governs
10 AWG copper
30A ampacity | 0.78% VD | 238.1V at load
Minimum wire by constraint
Required CMs: 2,688 CM. Formula: CM = (2 × K × I × L) / (V × 3%)
Wire size by run distance
Distance sensitivity for 30A on 240V 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
0.78
Max
2.93
Insight
Voltage drop by run distance shows an upward pattern, with a visible peak around 150 ft at 2.93.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 passes the modeled checks under the stated assumptions.
Step-by-step wire sizing
Load: 30A at 240V (single-phase), 25 ft, copper at 60°C
Step 1 — Ampacity: find smallest wire where derated ampacity ≥ 30A → 10 AWG (base 30A, no derating)
Step 2 — Voltage drop: allowed VD = 240V × 3% = 7.199999999999999V
CM = (2 × 12.9 × 30A × 25ft) / 7.199999999999999V = 2,688 CM → 14 AWG
Step 3 — Recommended: 10 AWG (ampacity governs)
Breaker: NEC 240.6(A): use 30A breaker (next standard size ≥ 30A)
Ground wire: NEC Table 250.122: 30A OCPD → EGC ≥ 10 AWG Cu (or 8 AWG Al)
Power loss: 54W in run — ~473 kWh/yr (~$66.22/yr @ $0.14/kWh)
Cost: ~$0.72/ft × 50 ft = ~$36 (2024 retail THHN)
Conduit: minimum 3/4" EMT for 3 conductors of 10 AWG
Verification: 30A ≥ 30A ✓ | VD 0.78% ≤ 3% ✓
Wire sizing FAQ
Why did the calculator recommend 10 AWG?
10 AWG is the smallest modeled copper conductor that satisfies ampacity and the 3% voltage-drop target.
10 AWG is the smallest modeled copper conductor that satisfies ampacity and the 3% voltage-drop target.
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.